AN EXPLORATION OF THE BIOMECHANICAL CHAIN IN WALKING AND RUNNING NEUROMECHANICAL FUNCTION FROM THE FEET UP TO THE TRUNK KARI HUSETH Department of Orthopedics Institute of Clinical Sciences Sahlgrenska Academy at University of Gothenburg Gothenburg 2025 Cover illustration: Pontus Andersson, Pontus Art Production AB Layout: Guðni Ólafsson, GO Grafik gudni@gografik.se Photos: Roy Tranberg QTM/Matlab figures: Guðni Rafn Harðarson Graphical illustrations: Pontus Andersson, Pontus Art Production AB Result figures (graphs): Kari Huseth Language editing support was obtained from the AI-based tool ChatGPT (OpenAI), which was used for grammar and style suggestions. All scientific content, analyses, and conclusions are the responsibility of the author. The path meanders into the mountain- always further, always onward Dancing through the juniper, tiptoeing over the marsh, searching over rock, hopping onto the tussock Catch me, catch me- it says, and sets off with new speed! And the summit plain lies with open doors-quietly stretching, in all directions - It carries on- deeper and deeper in…. Stien bukter seg innover fjellet- alltid lengre, alltid videre Danser frem gjennom eineren, lister på tå over myren, famler ut over svaberg, hopper på en tue. Fang meg, fang meg- sier den, og setter av sted med ny fart! Og vidden ligger for åpne dører-stillferdig utstrakt til alle sider - Det bærer dypere og dypere inn.... 👥👥 FROM STIEN, GABRIEL SCOTT, 1925; ENGLISH TRANSLATION: KH, 2025 © Kari Huseth 2025 kari.huseth@gu.se ISBN 978-91-8115-364-4 (PRINT) ISBN 978-91-8115-365-1 (PDF) ENMÄRAN KV E Printed in Borås, Sweden 2025 Printed by Stema Specialtryck AB Trycksak3041 0234 S T Cover illustration: Pontus Andersson, Pontus Art Production AB Layout: Guðni Ólafsson, GO Grafik gudni@gografik.se Photos: Roy Tranberg QTM/Matlab figures: Guðni Rafn Harðarson Graphical illustrations: Pontus Andersson, Pontus Art Production AB Result figures (graphs): Kari Huseth Language editing support was obtained from the AI-based tool ChatGPT (OpenAI), which was used for grammar and style suggestions. All scientific content, analyses, and conclusions are the responsibility of the author. The path meanders into the mountain- always further, always onward Dancing through the juniper, tiptoeing over the marsh, searching over rock, hopping onto the tussock Catch me, catch me- it says, and sets off with new speed! And the summit plain lies with open doors-quietly stretching, in all directions - It carries on- deeper and deeper in…. Stien bukter seg innover fjellet- alltid lengre, alltid videre Danser frem gjennom eineren, lister på tå over myren, famler ut over svaberg, hopper på en tue. Fang meg, fang meg- sier den, og setter av sted med ny fart! Og vidden ligger for åpne dører-stillferdig utstrakt til alle sider - Det bærer dypere og dypere inn.... 👥👥 FROM STIEN, GABRIEL SCOTT, 1925; ENGLISH TRANSLATION: KH, 2025 © Kari Huseth 2025 kari.huseth@gu.se ISBN 978-91-8115-364-4 (PRINT) ISBN 978-91-8115-365-1 (PDF) Printed in Borås, Sweden 2025 Printed by Stema Specialtryck AB Contents Data collection; Studies I-IV 56 METHODS 57 Studies I-II 59 Studies III-IV 64 Abstract 2 STATISTICAL ANALYSIS 70 STUDY POPULATIONS 74 Sammanfattning på svenska 5 Summary of Results 78 Sammendrag på norsk 8 STUDY I 79 Abbreviations 11 STUDY II 81 STUDY III 85 Definitions in short 12 STUDY IV 91 List of papers 13 Discussion 100 RETHINKING THE BIOMECHANICAL CHAIN: Introduction 14 ABSORPTIVE COUPLING MODEL 105 MOVEMENT AND PHYSICAL THERAPY 15 METHODOLOGICAL CONSIDERATIONS 107 MOVEMENT AND MOVEMENT CONTROL 16 Strengths and limitations 112 MOVEMENT AND MOTOR VARIABILITY 17 MOVEMENT AND THE BIOMECHANICAL CHAIN MECHANISM 18 STRENGTHS 113 BIOMECHANICS OF LOCOMOTION 21 LIMITATIONS 114 LOCOMOTION AND FEET KINEMATICS 29 Conclusion 116 LOCOMOTION AND THE ACHILLES TENDON 32 Knowledge gap 40 Clinical implication 118 Aims 42 Future perspectives 122 Ethical approvals 44 Acknowledgement 126 Introduction to biomechanical tools 46 References 134 ELECTROMYOGRAPHY (EMG) 47 Surface EMG (sEMG) 47 Appendix 150 sEMG signal processing 49 Normalization 50 Papers 164 Motion capture system (MOCAP) 51 Contents Data collection; Studies I-IV 56 METHODS 57 Studies I-II 59 Studies III-IV 64 Abstract 2 STATISTICAL ANALYSIS 70 STUDY POPULATIONS 74 Sammanfattning på svenska 5 Summary of Results 78 Sammendrag på norsk 8 STUDY I 79 Abbreviations 11 STUDY II 81 STUDY III 85 Definitions in short 12 STUDY IV 91 List of papers 13 Discussion 100 RETHINKING THE BIOMECHANICAL CHAIN: Introduction 14 ABSORPTIVE COUPLING MODEL 105 MOVEMENT AND PHYSICAL THERAPY 15 METHODOLOGICAL CONSIDERATIONS 107 MOVEMENT AND MOVEMENT CONTROL 16 Strengths and limitations 112 MOVEMENT AND MOTOR VARIABILITY 17 MOVEMENT AND THE BIOMECHANICAL CHAIN MECHANISM 18 STRENGTHS 113 BIOMECHANICS OF LOCOMOTION 21 LIMITATIONS 114 LOCOMOTION AND FEET KINEMATICS 29 Conclusion 116 LOCOMOTION AND THE ACHILLES TENDON 32 Knowledge gap 40 Clinical implication 118 Aims 42 Future perspectives 122 Ethical approvals 44 Acknowledgement 126 Introduction to biomechanical tools 46 References 134 ELECTROMYOGRAPHY (EMG) 47 Surface EMG (sEMG) 47 Appendix 150 sEMG signal processing 49 Normalization 50 Papers 164 Motion capture system (MOCAP) 51 Abstract Thirty-seven individuals with unilateral Achilles tendon rupture participated in Study III, which investigated the side-to-side differences Human gait and posture depend on coordinated interactions within the in neuromechanical function during walking and running approximately kinematic chain, where movement and force are transferred from the one year after the tendon injury using synchronized EMG, 3D motion feet upward through the lower limbs to the trunk. As the base of support, capture, and force plate analysis. This study revealed increased the feet play a central role in initiating these dynamics, yet the extent gastrocnemius activation and reduced ankle range of motion of the to which changes in foot mechanics affect more proximal segments affected limb during walking, alongside with decreased plantarflexor remains unclear. This thesis aimed to investigate how alterations in moments during running. EMG and joint kinetics showed greater foot kinematics influence the motor behavior along the biomechanical variability than kinematics, suggesting compensatory strategies that chain-from distal to proximal segments-including the ankle, knee, hip, preserve overall gait symmetry. and trunk during functional lower limb tasks and locomotion. A subset of 22 participants from the same cohort as in Study III, Two methodological approaches were used to support this objective. were included in  Study IV, which extended the analysis along the Twelve healthy adults participated in these studies. Both used biomechanical chain-from the feet to trunk-using bilateral EMG signals standardized surface electromyography (EMG), to assess neuromuscular from eight muscles, joint power and moments, support moment, activation. Study I compared maximum voluntary isometric contraction and joint range of motion. During walking, the affected limb showed (MVIC) for EMG normalization in supine and standing positions, while reduced ankle and knee power, diminished total support moments, Study II examined the influence of static foot postures (neutral, and decreased ankle range of motion, with increased gastrocnemius pronated, supinated) on muscle activation during a standardized step- activation and lower EMG variability in the soleus, indicating more rigid up maneuver. The results revealed no systematic differences in terms of and stereotyped motor control. Trunk-level adaptations were limited, and EMG amplitude between the supine and standing MVIC positions, and no consistent patterns of altered proximal coordination were observed. no major effect of foot posture on trunk muscle activation-even though Individuals displayed phase- and task-specific neuromechanical more consistent effects were observed in the lower extremity. deficits primarily in the distal limb, especially during walking. Running revealed fewer between-limb asymmetries, however with persisting Taken together, these findings support the robustness of MVIC ankle-level deficits and altered control strategies. Taken together, these normalization and suggest that foot configuration primarily modulates findings highlight long-term, task-specific adaptations after Achilles distal, rather than proximal, muscle activity. tendon rupture, with distal changes-especially at the ankle-playing a This framework was then applied to individuals one year after a unilateral key role in altered neuromechanical control during walking and running. Achilles tendon rupture; a condition known to impair ankle function and In contrast, proximal adaptations were modest, inconsistent, and varied disrupt gait propulsion. EMG was used to assess muscle activation in considerably between individuals. target muscles, while an optical motion capture system was employed The present thesis demonstrates that alterations in foot mechanics- to measure kinematic and kinetic variables. particularly in the ankle joint- have a significant impact on distal neuromuscular control during gait, especially after an Achilles tendon 2 ABSTRACT ABSTRACT 3 Abstract Thirty-seven individuals with unilateral Achilles tendon rupture participated in Study III, which investigated the side-to-side differences Human gait and posture depend on coordinated interactions within the in neuromechanical function during walking and running approximately kinematic chain, where movement and force are transferred from the one year after the tendon injury using synchronized EMG, 3D motion feet upward through the lower limbs to the trunk. As the base of support, capture, and force plate analysis. This study revealed increased the feet play a central role in initiating these dynamics, yet the extent gastrocnemius activation and reduced ankle range of motion of the to which changes in foot mechanics affect more proximal segments affected limb during walking, alongside with decreased plantarflexor remains unclear. This thesis aimed to investigate how alterations in moments during running. EMG and joint kinetics showed greater foot kinematics influence the motor behavior along the biomechanical variability than kinematics, suggesting compensatory strategies that chain-from distal to proximal segments-including the ankle, knee, hip, preserve overall gait symmetry. and trunk during functional lower limb tasks and locomotion. A subset of 22 participants from the same cohort as in Study III, Two methodological approaches were used to support this objective. were included in  Study IV, which extended the analysis along the Twelve healthy adults participated in these studies. Both used biomechanical chain-from the feet to trunk-using bilateral EMG signals standardized surface electromyography (EMG), to assess neuromuscular from eight muscles, joint power and moments, support moment, activation. Study I compared maximum voluntary isometric contraction and joint range of motion. During walking, the affected limb showed (MVIC) for EMG normalization in supine and standing positions, while reduced ankle and knee power, diminished total support moments, Study II examined the influence of static foot postures (neutral, and decreased ankle range of motion, with increased gastrocnemius pronated, supinated) on muscle activation during a standardized step- activation and lower EMG variability in the soleus, indicating more rigid up maneuver. The results revealed no systematic differences in terms of and stereotyped motor control. Trunk-level adaptations were limited, and EMG amplitude between the supine and standing MVIC positions, and no consistent patterns of altered proximal coordination were observed. no major effect of foot posture on trunk muscle activation-even though Individuals displayed phase- and task-specific neuromechanical more consistent effects were observed in the lower extremity. deficits primarily in the distal limb, especially during walking. Running revealed fewer between-limb asymmetries, however with persisting Taken together, these findings support the robustness of MVIC ankle-level deficits and altered control strategies. Taken together, these normalization and suggest that foot configuration primarily modulates findings highlight long-term, task-specific adaptations after Achilles distal, rather than proximal, muscle activity. tendon rupture, with distal changes-especially at the ankle-playing a This framework was then applied to individuals one year after a unilateral key role in altered neuromechanical control during walking and running. Achilles tendon rupture; a condition known to impair ankle function and In contrast, proximal adaptations were modest, inconsistent, and varied disrupt gait propulsion. EMG was used to assess muscle activation in considerably between individuals. target muscles, while an optical motion capture system was employed The present thesis demonstrates that alterations in foot mechanics- to measure kinematic and kinetic variables. particularly in the ankle joint- have a significant impact on distal neuromuscular control during gait, especially after an Achilles tendon 2 ABSTRACT ABSTRACT 3 rupture. In contrast, proximal adaptations were limited and variable. Sammanfattning på svenska These findings emphasize the importance of rehabilitation strategies focused on distal tendon function and neuromuscular control, while acknowledging individual differences in motor variability. In addition, Mänsklig gång och hållning är beroende av koordinerade interaktioner the methodological work confirmed that MVIC normalization yields inom den kinematiska kedjan, där rörelse och kraft överförs från consistent results across testing positions, reinforcing its suitability for fötterna upp genom nedre extremiteterna till bålen. Som stödjepunkt reliable EMG-based assessments in both research and clinical contexts. spelar fötterna en central roll i att initiera denna dynamik, men i vilken utsträckning förändringar i fotens mekanik påverkar mer proximala Keywords: segment är fortfarande oklart. Biomechanical chain, human gait, foot posture, Achilles tendon rupture, electromyography, kinematics and kinetics, neuromechanical Syftet med denna avhandling var att undersöka hur förändringar i adaptation, motor variability fotens kinematik påverkar motoriskt beteende längs den biomekaniska kedjan – från distala till proximala segment – inklusive fotled och upp ISBN 978-91-8115-364-4 (PRINT) till bål i samband med funktionella uppgifter för nedre extremitet och ISBN 978-91-8115-365-1 (PDF) under gång och löpning. Två metodologiska studier – Studie I och II-genomfördes för att stödja detta syfte. Tolv friska vuxna deltog i båda studierna, där standardiserad yt-EMG användes för att analysera neuromuskulär aktivering. Studie I jämförde metoder för maximal viljemässig isometrisk kontraktion (MVIC) för EMG-normalisering i liggande och stående positioner, medan Studie II undersökte hur statiska fotpositioner (neutral, pronerad, supinerad) påverkade muskelaktivitet under ett standardiserat uppstegstest. Resultaten visade inga systematiska skillnader i EMG-amplitud mellan liggande och stående MVIC-positioner, samt inga större effekter av fotposition på bålmuskulaturens aktivering-även om tydligare effekter observerades i nedre extremiteten. Sammantaget stödjer dessa fynd robustheten i MVIC-normalisering och antyder att fotposition främst påverkar distal snarare än proximal muskelaktivitet. Detta ramverk tillämpades därefter på individer ett år efter en unilateral akillesseneruptur-ett tillstånd som påverkar fotledsfunktion och stör gångens framåtdrivning. Elektromyografi användes för att analysera 4 ABSTRACT SAMMANFATTNING PÅ SVENSKA 5 rupture. In contrast, proximal adaptations were limited and variable. Sammanfattning på svenska These findings emphasize the importance of rehabilitation strategies focused on distal tendon function and neuromuscular control, while acknowledging individual differences in motor variability. In addition, Mänsklig gång och hållning är beroende av koordinerade interaktioner the methodological work confirmed that MVIC normalization yields inom den kinematiska kedjan, där rörelse och kraft överförs från consistent results across testing positions, reinforcing its suitability for fötterna upp genom nedre extremiteterna till bålen. Som stödjepunkt reliable EMG-based assessments in both research and clinical contexts. spelar fötterna en central roll i att initiera denna dynamik, men i vilken utsträckning förändringar i fotens mekanik påverkar mer proximala Keywords: segment är fortfarande oklart. Biomechanical chain, human gait, foot posture, Achilles tendon rupture, electromyography, kinematics and kinetics, neuromechanical Syftet med denna avhandling var att undersöka hur förändringar i adaptation, motor variability fotens kinematik påverkar motoriskt beteende längs den biomekaniska kedjan – från distala till proximala segment – inklusive fotled och upp ISBN 978-91-8115-364-4 (PRINT) till bål i samband med funktionella uppgifter för nedre extremitet och ISBN 978-91-8115-365-1 (PDF) under gång och löpning. Två metodologiska studier – Studie I och II-genomfördes för att stödja detta syfte. Tolv friska vuxna deltog i båda studierna, där standardiserad yt-EMG användes för att analysera neuromuskulär aktivering. Studie I jämförde metoder för maximal viljemässig isometrisk kontraktion (MVIC) för EMG-normalisering i liggande och stående positioner, medan Studie II undersökte hur statiska fotpositioner (neutral, pronerad, supinerad) påverkade muskelaktivitet under ett standardiserat uppstegstest. Resultaten visade inga systematiska skillnader i EMG-amplitud mellan liggande och stående MVIC-positioner, samt inga större effekter av fotposition på bålmuskulaturens aktivering-även om tydligare effekter observerades i nedre extremiteten. Sammantaget stödjer dessa fynd robustheten i MVIC-normalisering och antyder att fotposition främst påverkar distal snarare än proximal muskelaktivitet. Detta ramverk tillämpades därefter på individer ett år efter en unilateral akillesseneruptur-ett tillstånd som påverkar fotledsfunktion och stör gångens framåtdrivning. Elektromyografi användes för att analysera 4 ABSTRACT SAMMANFATTNING PÅ SVENSKA 5 muskelaktivitet i utvalda muskler, medan ett optiskt rörelsesystem under lokomotion, särskilt efter en akillesseneruptur. I kontrast var de användes för att mäta kinematiska och kinetiska variabler. proximala anpassningarna begränsade och varierade mellan individer. Fynden understryker vikten av rehabiliteringsstrategier, som fokuserar Studie III inkluderade 37 personer med unilateral akillesseneruptur på distala senors funktion och neuromuskulär kontroll, samtidigt och undersökte sidoskillnader i neuromekanisk funktion under som individuella skillnader i motorisk variabilitet beaktas. Dessutom gång och löpning ett år efter skadan, med hjälp av synkroniserad bekräftade det metodologiska arbetet att MVIC-normalisering ger EMG, 3D-rörelseanalys och kraftplattor. Studien visade ökad konsekventa resultat oberoende av testposition, vilket stärker dess gastrocnemiusaktivitet och reducerad fotledsrörelse i den drabbade lämplighet för tillförlitliga EMG-baserade bedömningar både i forskning sidan under gång, samt minskade plantarflexionsmoment under och kliniska sammanhang. löpning. EMG och ledkinetik visade större variation än kinematiken, vilket antyder kompenserande strategier för att bibehålla övergripande gångsymmetri. Ett delurval på 22 deltagare från samma kohort inkluderades i Studie IV, som utökade analysen längs den biomekaniska kedjan – från fot till bål – med bilateral EMG från åtta muskler, ledkraft och moment, stödjande moment och ledrörelser. Under gång visade den drabbade sidan minskad kraft i fotled och knä, reducerade stödmoment samt begränsad rörlighet i fotleden, tillsammans med ökad gastrocnemiusaktivitet och lägre EMG-variabilitet i soleus, vilket tyder på ett mer stelt och stereotypt motoriskt mönster. Anpassningar på bålnivå var begränsade och inga konsekventa mönster för förändrad proximal koordination observerades. Individer uppvisade fas-och uppgiftsspecifika neuromekaniska underskott, främst i den distala extremiteten, särskilt under gång. Färre asymmetrier observerades under löpning, även om kvarstående begränsningar i fotledsfunktion och förändrade kontrollstrategier bestod. Sammantaget belyser dessa fynd långvariga, uppgiftsspecifika anpassningar efter akillesseneruptur, där förändringar i distala segment-särskilt i fotleden – spelar en central roll avseende förändrad neuromuskulär kontroll under gång och löpning. Däremot var proximala anpassningar måttliga, inkonsekventa och visade stor individuell variation. Denna avhandling visar att förändringar i fotens mekanik – främst i fotleden – har en betydande påverkan på distal neuromuskulär kontroll 6 SAMMANFATTNING PÅ SVENSKA SAMMANFATTNING PÅ SVENSKA 7 muskelaktivitet i utvalda muskler, medan ett optiskt rörelsesystem under lokomotion, särskilt efter en akillesseneruptur. I kontrast var de användes för att mäta kinematiska och kinetiska variabler. proximala anpassningarna begränsade och varierade mellan individer. Fynden understryker vikten av rehabiliteringsstrategier, som fokuserar Studie III inkluderade 37 personer med unilateral akillesseneruptur på distala senors funktion och neuromuskulär kontroll, samtidigt och undersökte sidoskillnader i neuromekanisk funktion under som individuella skillnader i motorisk variabilitet beaktas. Dessutom gång och löpning ett år efter skadan, med hjälp av synkroniserad bekräftade det metodologiska arbetet att MVIC-normalisering ger EMG, 3D-rörelseanalys och kraftplattor. Studien visade ökad konsekventa resultat oberoende av testposition, vilket stärker dess gastrocnemiusaktivitet och reducerad fotledsrörelse i den drabbade lämplighet för tillförlitliga EMG-baserade bedömningar både i forskning sidan under gång, samt minskade plantarflexionsmoment under och kliniska sammanhang. löpning. EMG och ledkinetik visade större variation än kinematiken, vilket antyder kompenserande strategier för att bibehålla övergripande gångsymmetri. Ett delurval på 22 deltagare från samma kohort inkluderades i Studie IV, som utökade analysen längs den biomekaniska kedjan – från fot till bål – med bilateral EMG från åtta muskler, ledkraft och moment, stödjande moment och ledrörelser. Under gång visade den drabbade sidan minskad kraft i fotled och knä, reducerade stödmoment samt begränsad rörlighet i fotleden, tillsammans med ökad gastrocnemiusaktivitet och lägre EMG-variabilitet i soleus, vilket tyder på ett mer stelt och stereotypt motoriskt mönster. Anpassningar på bålnivå var begränsade och inga konsekventa mönster för förändrad proximal koordination observerades. Individer uppvisade fas-och uppgiftsspecifika neuromekaniska underskott, främst i den distala extremiteten, särskilt under gång. Färre asymmetrier observerades under löpning, även om kvarstående begränsningar i fotledsfunktion och förändrade kontrollstrategier bestod. Sammantaget belyser dessa fynd långvariga, uppgiftsspecifika anpassningar efter akillesseneruptur, där förändringar i distala segment-särskilt i fotleden – spelar en central roll avseende förändrad neuromuskulär kontroll under gång och löpning. Däremot var proximala anpassningar måttliga, inkonsekventa och visade stor individuell variation. Denna avhandling visar att förändringar i fotens mekanik – främst i fotleden – har en betydande påverkan på distal neuromuskulär kontroll 6 SAMMANFATTNING PÅ SVENSKA SAMMANFATTNING PÅ SVENSKA 7 Sammendrag på norsk bevegelsessystem ble benyttet for å måle kinematiske og kinetiske variabler. Studie III  inkluderte 37 personer med unilateral akillesseneruptur og Menneskelig gange og kroppsholdning er avhengig av et koordinerte undersøkte sideforskjeller i nevromekanisk funksjon under gange samspill i den kinematiske kjeden, hvor bevegelse og kraft overføres og løping, omtrent ett år etter skade. Det ble anvendt synkronisert fra føttene via underekstremitetene til overkroppen. Føttene fungerer EMG, 3D-bevegelsesanalyse og kraftplater. Studien viste økt aktivitet som kroppens støtteflate og spiller en nøkkelrolle i å initiere denne i gastrocnemius og redusert ankelbevegelighet på den affiserte dynamikken. Det er fortsatt uklart i hvilken grad endringer i fotens siden under gange. Under løping ble det observert redusert plantar mekaniske egenskaper påvirker mer proksimale segmenter . Formålet fleksjonsmoment. Variasjonen i EMG og leddkinetikk var større enn i med denne avhandlingen var å undersøke hvordan variasjoner i kinematikken, noe som antyder bruk av kompenserende strategier for fotens kinematikk påvirker motorisk respons langs den biomekaniske å opprettholde gangsymmetri. kjeden – fra distale til proksimale segmenter – inkludert ankel, kne, hofte og truncus. Dette ble studert under funksjonelle oppgaver for Et utvalg på 22 deltakere fra samme kohort ble inkludert i  Studie IV, underekstremitetene samt under gange og løping. og utvidet analysen til å omfatte hele den biomekaniske kjeden – fra fot til truncus. Ved hjelp av bilateral EMG fra åtte muskler samt For å belyse dette ble to metodologiske studier gjennomført med målinger av leddkraft og leddmoment, støttemoment og leddutslag, tolv friske voksne. begge studiene ble standardisert overflate- ble det identifisert redusert kraftutvikling i ankel og kne, reduserte elektromyografi (EMG) benyttet for å analysere nevromuskulær støttemoment og begrenset leddutslag i ankelen på den affiserte aktivering i relevante muskelgrupper.Studie I  sammenlignet metoder siden under gange. Dette ble ledsaget av økt gastrocnemiusaktivitet for maksimal viljestyrt isometrisk kontraksjon (MVIC) for EMG- og lavere EMG-variabilitet i soleus, noe som indikerer et mer stivt og normalisering i liggende og stående stilling, mens Studie II undersøkte stereotypisk motorisk mønster. På truncusnivå ble det observert hvordan statiske fotposisjoner (nøytral, pronert, supinert) påvirket begrensede tilpasninger, uten konsistente mønstre for endret muskelaktivitet under en standardisert steptest. Resultatene viste proksimal koordinasjon. Deltakerne viste fase- og oppgavespesifikke ingen systematisk forskjell i EMG-amplitude i liggende og stående nevromekaniske underskudd, hovedsakelig i den distale ekstremiteten, MVIC-stilling. Fotstilling hadde ingen systematisk effekt på aktivering særlig under gange. Under løping ble det observert færre asymmetrier, av overkroppens muskulatur. Det ble observert noe effekt i muskulatur selv om underskudd i ankelleddet og endrede kontrollstrategier fortsatt underekstremitetene. Samlet støtter disse funnene robustheten i var til stede. Samlet viser funnene langvarige og oppgavespesifikke MVIC-normalisering og antyder at fotstilling først og fremst påvirker tilpasninger etter akillesseneruptur, der endringer i de distale distal fremfor proksimal muskelaktivitet. segmentene – særlig i ankelen – spiller en sentral rolle i endret Rammeverket ble videre anvendt på en gruppe personer ett år etter nevromuskulær kontroll. Proksimale tilpasninger fremstod som en unilateral akillesseneruptur – en skade som ofte fører til redusert moderate og uensartede, med markerte individuelle variasjon. ankelfunksjon og endret gangmønster. Elektromyografi ble brukt Denne avhandling viser at endringer i fotens mekanikk – særlig i ankelen – for å analysere muskelaktivitet i utvalgte muskler, mens et optisk har betydelig innvirkning på distal nevromuskulær kontroll under gange, 8 SAMMENDRAG PÅ NORSK SAMMENDRAG PÅ NORSK 9 Sammendrag på norsk bevegelsessystem ble benyttet for å måle kinematiske og kinetiske variabler. Studie III  inkluderte 37 personer med unilateral akillesseneruptur og Menneskelig gange og kroppsholdning er avhengig av et koordinerte undersøkte sideforskjeller i nevromekanisk funksjon under gange samspill i den kinematiske kjeden, hvor bevegelse og kraft overføres og løping, omtrent ett år etter skade. Det ble anvendt synkronisert fra føttene via underekstremitetene til overkroppen. Føttene fungerer EMG, 3D-bevegelsesanalyse og kraftplater. Studien viste økt aktivitet som kroppens støtteflate og spiller en nøkkelrolle i å initiere denne i gastrocnemius og redusert ankelbevegelighet på den affiserte dynamikken. Det er fortsatt uklart i hvilken grad endringer i fotens siden under gange. Under løping ble det observert redusert plantar mekaniske egenskaper påvirker mer proksimale segmenter . Formålet fleksjonsmoment. Variasjonen i EMG og leddkinetikk var større enn i med denne avhandlingen var å undersøke hvordan variasjoner i kinematikken, noe som antyder bruk av kompenserende strategier for fotens kinematikk påvirker motorisk respons langs den biomekaniske å opprettholde gangsymmetri. kjeden – fra distale til proksimale segmenter – inkludert ankel, kne, hofte og truncus. Dette ble studert under funksjonelle oppgaver for Et utvalg på 22 deltakere fra samme kohort ble inkludert i  Studie IV, underekstremitetene samt under gange og løping. og utvidet analysen til å omfatte hele den biomekaniske kjeden – fra fot til truncus. Ved hjelp av bilateral EMG fra åtte muskler samt For å belyse dette ble to metodologiske studier gjennomført med målinger av leddkraft og leddmoment, støttemoment og leddutslag, tolv friske voksne. begge studiene ble standardisert overflate- ble det identifisert redusert kraftutvikling i ankel og kne, reduserte elektromyografi (EMG) benyttet for å analysere nevromuskulær støttemoment og begrenset leddutslag i ankelen på den affiserte aktivering i relevante muskelgrupper.Studie I  sammenlignet metoder siden under gange. Dette ble ledsaget av økt gastrocnemiusaktivitet for maksimal viljestyrt isometrisk kontraksjon (MVIC) for EMG- og lavere EMG-variabilitet i soleus, noe som indikerer et mer stivt og normalisering i liggende og stående stilling, mens Studie II undersøkte stereotypisk motorisk mønster. På truncusnivå ble det observert hvordan statiske fotposisjoner (nøytral, pronert, supinert) påvirket begrensede tilpasninger, uten konsistente mønstre for endret muskelaktivitet under en standardisert steptest. Resultatene viste proksimal koordinasjon. Deltakerne viste fase- og oppgavespesifikke ingen systematisk forskjell i EMG-amplitude i liggende og stående nevromekaniske underskudd, hovedsakelig i den distale ekstremiteten, MVIC-stilling. Fotstilling hadde ingen systematisk effekt på aktivering særlig under gange. Under løping ble det observert færre asymmetrier, av overkroppens muskulatur. Det ble observert noe effekt i muskulatur selv om underskudd i ankelleddet og endrede kontrollstrategier fortsatt underekstremitetene. Samlet støtter disse funnene robustheten i var til stede. Samlet viser funnene langvarige og oppgavespesifikke MVIC-normalisering og antyder at fotstilling først og fremst påvirker tilpasninger etter akillesseneruptur, der endringer i de distale distal fremfor proksimal muskelaktivitet. segmentene – særlig i ankelen – spiller en sentral rolle i endret Rammeverket ble videre anvendt på en gruppe personer ett år etter nevromuskulær kontroll. Proksimale tilpasninger fremstod som en unilateral akillesseneruptur – en skade som ofte fører til redusert moderate og uensartede, med markerte individuelle variasjon. ankelfunksjon og endret gangmønster. Elektromyografi ble brukt Denne avhandling viser at endringer i fotens mekanikk – særlig i ankelen – for å analysere muskelaktivitet i utvalgte muskler, mens et optisk har betydelig innvirkning på distal nevromuskulær kontroll under gange, 8 SAMMENDRAG PÅ NORSK SAMMENDRAG PÅ NORSK 9 spesielt etter en akillesseneruptur. I motsetning til dette var proksimale Abbreviations tilpasninger begrensede og varierte mellom individene. Funnene understreker viktigheten av rehabiliteringsstrategier som fokuserer på distale seners funksjon og nevromuskulær kontroll, samtidig som ABD abduction individuelle forskjeller i motorisk variabilitet tas i betraktning. ADD adduction ATR Achilles tendon rupture ATRS Achilles Tendon Total Rupture Scores BCG body center of gravity CAV coordination variablity COM center of mass DF dorsal flexion EMG electromyography EV eversion EXT extension FLEX flexion IC initial contact IN inversion MOCAP motion capture MS midstance MUAP motor unit action potential OA osteoarthritis PF plantar flexion RMS root mean square ROM range of motion RSA radiostereometric analysis TO toe-off TROM total range of motion 10 SAMMENDRAG PÅ NORSK ABBREVIATIONS 11 spesielt etter en akillesseneruptur. I motsetning til dette var proksimale Abbreviations tilpasninger begrensede og varierte mellom individene. Funnene understreker viktigheten av rehabiliteringsstrategier som fokuserer på distale seners funksjon og nevromuskulær kontroll, samtidig som ABD abduction individuelle forskjeller i motorisk variabilitet tas i betraktning. ADD adduction ATR Achilles tendon rupture ATRS Achilles Tendon Total Rupture Scores BCG body center of gravity CAV coordination variablity COM center of mass DF dorsal flexion EMG electromyography EV eversion EXT extension FLEX flexion IC initial contact IN inversion MOCAP motion capture MS midstance MUAP motor unit action potential OA osteoarthritis PF plantar flexion RMS root mean square ROM range of motion RSA radiostereometric analysis TO toe-off TROM total range of motion 10 SAMMENDRAG PÅ NORSK ABBREVIATIONS 11 Definitions in short List of papers Chain theory A mechanically connected chain of segments-from the foot to the head-that functions as an integrated, This thesis is based on the following studies, referred to in the text by coordinated unit their Roman numerals. Electromyography The study of muscle function through the investigation of the electrical signals generated within the muscles I. Huseth K, Aagaard P, Gutke A, Karlsson J, Tranberg R. Gravity G ravity refers to the attractive force that pulls objects Assessment of neuromuscular activity during maximal toward the center of the planet. Newton’s Law of isometric contraction in supine vs standing body positon. Universal Gravitation J Electromyogr Kinesiol. 2020, 50:102365. Ground reaction force The ground reaction force is the force exerted by the https://doi.org/10.1016/j.jelekin.2019.102365 ground on a body in contact with it. This force is equal in magnitude and opposite in direction to the force that the body exerts on the ground II. Huseth K, Aagaard P, Gutke A, Karlsson J, Zügner R, Tranberg R. Kinematics The study of motion without considering the forces that The effect of foot pronation and supination during vertical cause it step maneuvers on muscle activation in selected trunk and lower extremity muscles Kinetics The study of the forces that cause or influence motion Submitted Motor variability T he variance of movements generated by an individual under a given task condition III. Huseth K, Hardarson GR, Aagaard P, Gutke A, Zügner R, Karlsson J, Muscle function T he ability of muscles to produce force, generate Nilsson Helander K, Larsson L, Brorsson A, Tranberg R. movement, and stabilize joints to support posture and physical activity Interlimb differences in gait kinematics, kinetics, and muscle Neuromechanical T he interactions between the nervous system (neu-), activation during walking and running one year after acute and the musculoskeletal system (mechanical) to unilateral Achilles tendon rupture. produce movement and maintain posture J Ortop Surg Res. 2025, 20 (1): 819. Newton’s 2nd Law Describes the relationship between force, mass, and doi: 10.1186/s13018-025-06221-0 acceleration, stating that the force acting on an object is equal to its mass multiplied by its acceleration, IV. Huseth K, Hardarson GR, Aagaard P, Gutke A, Zügner R, Karlsson J, (F = m*a) Nilsson Helander K, Larsson L, Brorsson A, Tranberg R. Newton’s 3rd Law For every action, there is an equal and opposite reaction; when one body exerts a force on another, Side-to-side differences in neuromechanical function the second body exerts an equal force in the opposite inlower limbs and trunk while walking and running one-ye ar direction after acute unilateral Achilles tendon rupture. Postural control Study of intrinsic mechanisms of the human body that Manuscript counteract gravity, with a special focus on the function of the muscular system for the maintenance of balance when posture is exposed to perturbation 12 DEFINITIONS IN SHORT LIST OF PAPERS 13 Definitions in short List of papers Chain theory A mechanically connected chain of segments-from the foot to the head-that functions as an integrated, This thesis is based on the following studies, referred to in the text by coordinated unit their Roman numerals. Electromyography The study of muscle function through the investigation of the electrical signals generated within the muscles I. Huseth K, Aagaard P, Gutke A, Karlsson J, Tranberg R. Gravity G ravity refers to the attractive force that pulls objects Assessment of neuromuscular activity during maximal toward the center of the planet. Newton’s Law of isometric contraction in supine vs standing body positon. Universal Gravitation J Electromyogr Kinesiol. 2020, 50:102365. Ground reaction force The ground reaction force is the force exerted by the https://doi.org/10.1016/j.jelekin.2019.102365 ground on a body in contact with it. This force is equal in magnitude and opposite in direction to the force that the body exerts on the ground II. Huseth K, Aagaard P, Gutke A, Karlsson J, Zügner R, Tranberg R. Kinematics The study of motion without considering the forces that The effect of foot pronation and supination during vertical cause it step maneuvers on muscle activation in selected trunk and lower extremity muscles Kinetics The study of the forces that cause or influence motion Submitted Motor variability T he variance of movements generated by an individual under a given task condition III. Huseth K, Hardarson GR, Aagaard P, Gutke A, Zügner R, Karlsson J, Muscle function T he ability of muscles to produce force, generate Nilsson Helander K, Larsson L, Brorsson A, Tranberg R. movement, and stabilize joints to support posture and physical activity Interlimb differences in gait kinematics, kinetics, and muscle Neuromechanical T he interactions between the nervous system (neu-), activation during walking and running one year after acute and the musculoskeletal system (mechanical) to unilateral Achilles tendon rupture. produce movement and maintain posture J Ortop Surg Res. 2025, 20 (1): 819. Newton’s 2nd Law Describes the relationship between force, mass, and doi: 10.1186/s13018-025-06221-0 acceleration, stating that the force acting on an object is equal to its mass multiplied by its acceleration, IV. Huseth K, Hardarson GR, Aagaard P, Gutke A, Zügner R, Karlsson J, (F = m*a) Nilsson Helander K, Larsson L, Brorsson A, Tranberg R. Newton’s 3rd Law For every action, there is an equal and opposite reaction; when one body exerts a force on another, Side-to-side differences in neuromechanical function the second body exerts an equal force in the opposite inlower limbs and trunk while walking and running one-ye ar direction after acute unilateral Achilles tendon rupture. Postural control Study of intrinsic mechanisms of the human body that Manuscript counteract gravity, with a special focus on the function of the muscular system for the maintenance of balance when posture is exposed to perturbation 12 DEFINITIONS IN SHORT LIST OF PAPERS 13 1. Introduction MOVEMENT AND PHYSICAL THERAPY Most of us rarely consider the intricate coordination required between the feet, knees, hips, and trunk that underlies human gait. We effortlessly place one foot in front of the other to walk to the store or sprint to catch a bus, without consciously considering how these segments interact to keep us upright and moving smoothly. This seamless integration of body segments is often taken for granted, at least until something disrupts it. An injury, such as a torn ligament or ruptured tendon, or the onset of a musculoskeletal condition, such as osteoarthritis (OA) can suddenly expose just how complex and finely tuned this system truly is. Only when the movement is disrupted whether by injury, illness, or degeneration-do we become acutely aware of the body’s profound reliance on neuromechanical harmony to carry out even the most routine tasks. Human locomotion is a complex process involving the integration of neuromuscular control, muscular strength and endurance, coordinated joint movements, postural balance, and biomechanical principles grounded in physics and chemistry (1, 2). It is the product of evolutionary refinement, driven by necessity, curiosity, and adaptation (3). What we typically experience as effortless movement is, in reality, the outcome of a finely tuned interplay between body structures and function (4). Our body consists of 206 skeletal bones and more than 650 muscles, integrated to form chains of movement that enable activities of daily life, recreation, work and play (5). Humans are able to adapt and coordinate their anatomy to crawl, walk, run, climb, jump, dance – each movement is an reflection of the intricate mechanics of the biomechanical locomotor chain (6). It may be that when we no longer know what to do, we have come to our real work. Human movement science is fundamental to physical therapy practice And when we no longer know which way to go, and to overall health and well-being as well. Physical therapy uses move- we have begun our real journey. ment both to assess dysfunction and as a primary intervention to restore 👥👥 WENDEL BERRY function, relieve pain, and enhance quality of life. Through targeted exer- 14 INTRODUCTION KARI HUSETH 15 1. Introduction MOVEMENT AND PHYSICAL THERAPY Most of us rarely consider the intricate coordination required between the feet, knees, hips, and trunk that underlies human gait. We effortlessly place one foot in front of the other to walk to the store or sprint to catch a bus, without consciously considering how these segments interact to keep us upright and moving smoothly. This seamless integration of body segments is often taken for granted, at least until something disrupts it. An injury, such as a torn ligament or ruptured tendon, or the onset of a musculoskeletal condition, such as osteoarthritis (OA) can suddenly expose just how complex and finely tuned this system truly is. Only when the movement is disrupted whether by injury, illness, or degeneration-do we become acutely aware of the body’s profound reliance on neuromechanical harmony to carry out even the most routine tasks. Human locomotion is a complex process involving the integration of neuromuscular control, muscular strength and endurance, coordinated joint movements, postural balance, and biomechanical principles grounded in physics and chemistry (1, 2). It is the product of evolutionary refinement, driven by necessity, curiosity, and adaptation (3). What we typically experience as effortless movement is, in reality, the outcome of a finely tuned interplay between body structures and function (4). Our body consists of 206 skeletal bones and more than 650 muscles, integrated to form chains of movement that enable activities of daily life, recreation, work and play (5). Humans are able to adapt and coordinate their anatomy to crawl, walk, run, climb, jump, dance – each movement is an reflection of the intricate mechanics of the biomechanical locomotor chain (6). It may be that when we no longer know what to do, we have come to our real work. Human movement science is fundamental to physical therapy practice And when we no longer know which way to go, and to overall health and well-being as well. Physical therapy uses move- we have begun our real journey. ment both to assess dysfunction and as a primary intervention to restore 👥👥 WENDEL BERRY function, relieve pain, and enhance quality of life. Through targeted exer- 14 INTRODUCTION KARI HUSETH 15 cises, manual techniques, and education, physical therapists help indi- Postural control also depends on what can be called feed-forward viduals regain mobility, prevent injury, and improve physical performance mechanisms that use anticipatory signals to predict how impending (7, 8). Physical therapy therefore relies on the integrated and coordinated movements might disrupt the balance system (4). Each individual carries function of the body across multiple levels (9). a unique movement history, a learned rhythm that shapes and creates an imprint in the individual neuro-muscular system (13). Analyzing human movement presents significant challenges due to its inherent complexity and the dynamic interactions between bodily systems. MOVEMENT AND MOTOR VARIABILITY One challenge is the research field of biomechanics, which can be An individual’s ability to adapt the body movements is a significant defined as ”the interdisciplinary research that describes, analyzes, and advantage and asset in everyday skill-solving and, of course, as well (14) assesses human movement” (1, 10). Also in terms of biomechanics the as recreational and professional sports . Dynamic changes are breakdown of study areas is multifaceted and diverse. One such area of supported by the plasticity of human biological systems, enabling the adaptation of each individual’s actions (15, 16)interest is the study of locomotion (1). . Motor variability can be defined as the variance of movements generated by an individual under a given task condition (17-19). The variability observed across repeated MOVEMENT AND MOVEMENT CONTROL movements is not merely a random and unwanted noise, but may reflect an underlying structure that takes advantage of the motor system’s Locomotion like any other human movement pattern is dependent upon built-in redundancy. It is the body’s ability to achieve the same task a control mechanism with an anchorage in the body’s postural control through multiple combinations of muscles and joint movements (20, 21). (4). Posture can be defined as the study of intrinsic mechanisms of the This suggests that the co-existence of determinism and variability in human body that counteract gravity, with a special focus on the function co-ordinated behavior may have important functional relevance, rather of the muscular system for the maintenance of balance when posture than representing purely random fluctuations (22, 23). is exposed to perturbation (10). Taken together, this means that afferent input (sensory signals) is transmitted to the central nervous system, An overview of sports biomechanics research has highlighted variability where it is processed, leading to efferent output (motor signals) that in movement-specifically in throwing skills, basketball shots, and elicit the postural responses in the muscular system. locomotion-suggesting that movement and coordination variability can be functional (24). Such functionality may enable better adaptation to Perturbations to postural control and human gait can be described as environmental changes, reduce injury risk, and support adjustments in encountering a variety of different and unexpected obstacles (11, 12). individual coordination patterns. Bartlett et al. argued that movement Postural control demands are task-specific and vary accordingly to and co-ordination variability are, or could at least be, functional (24). the interpretation of the nerve feedback system (11). As such, walking This functionality may allow for better adaptation to environmental and running require sufficient inherent balance control to ensure that changes, reduce the risk of injury, and facilitate alterations in individual erect posture is sustained during the propulsive motor actions. Postural co-ordination patterns. control relies on previous movement experience, from early mobility to present activity (13). 16 INTRODUCTION KARI HUSETH 17 cises, manual techniques, and education, physical therapists help indi- Postural control also depends on what can be called feed-forward viduals regain mobility, prevent injury, and improve physical performance mechanisms that use anticipatory signals to predict how impending (7, 8). Physical therapy therefore relies on the integrated and coordinated movements might disrupt the balance system (4). Each individual carries function of the body across multiple levels (9). a unique movement history, a learned rhythm that shapes and creates an imprint in the individual neuro-muscular system (13). Analyzing human movement presents significant challenges due to its inherent complexity and the dynamic interactions between bodily systems. MOVEMENT AND MOTOR VARIABILITY One challenge is the research field of biomechanics, which can be An individual’s ability to adapt the body movements is a significant defined as ”the interdisciplinary research that describes, analyzes, and advantage and asset in everyday skill-solving and, of course, as well (14) assesses human movement” (1, 10). Also in terms of biomechanics the as recreational and professional sports . Dynamic changes are breakdown of study areas is multifaceted and diverse. One such area of supported by the plasticity of human biological systems, enabling the adaptation of each individual’s actions (15, 16)interest is the study of locomotion (1). . Motor variability can be defined as the variance of movements generated by an individual under a given task condition (17-19). The variability observed across repeated MOVEMENT AND MOVEMENT CONTROL movements is not merely a random and unwanted noise, but may reflect an underlying structure that takes advantage of the motor system’s Locomotion like any other human movement pattern is dependent upon built-in redundancy. It is the body’s ability to achieve the same task a control mechanism with an anchorage in the body’s postural control through multiple combinations of muscles and joint movements (20, 21). (4). Posture can be defined as the study of intrinsic mechanisms of the This suggests that the co-existence of determinism and variability in human body that counteract gravity, with a special focus on the function co-ordinated behavior may have important functional relevance, rather of the muscular system for the maintenance of balance when posture than representing purely random fluctuations (22, 23). is exposed to perturbation (10). Taken together, this means that afferent input (sensory signals) is transmitted to the central nervous system, An overview of sports biomechanics research has highlighted variability where it is processed, leading to efferent output (motor signals) that in movement-specifically in throwing skills, basketball shots, and elicit the postural responses in the muscular system. locomotion-suggesting that movement and coordination variability can be functional (24). Such functionality may enable better adaptation to Perturbations to postural control and human gait can be described as environmental changes, reduce injury risk, and support adjustments in encountering a variety of different and unexpected obstacles (11, 12). individual coordination patterns. Bartlett et al. argued that movement Postural control demands are task-specific and vary accordingly to and co-ordination variability are, or could at least be, functional (24). the interpretation of the nerve feedback system (11). As such, walking This functionality may allow for better adaptation to environmental and running require sufficient inherent balance control to ensure that changes, reduce the risk of injury, and facilitate alterations in individual erect posture is sustained during the propulsive motor actions. Postural co-ordination patterns. control relies on previous movement experience, from early mobility to present activity (13). 16 INTRODUCTION KARI HUSETH 17 Differences in walking speed and footwear, for example, have been functions together as a co-ordinated unit (30). The human biomechanical shown to influence kinematic and kinetic patterns, with some individuals chain from the metatarsal joints of the feet to the most proximal cervical adopting to a more flexed knee joint angles and higher extensor joint consists of more than 40 degrees of joint freedom movement. The moments at the knee, while others walk with a more extended knee joint sizeable number of joint freedoms enables the foot to adjust to various angles and lowerknee extensor moments (25). challenging surfaces, while at the same time allowing the biomechanical chain to function as a whole to maintain the body’s center of gravity (BCG) During running, limb-specific coordination variability (CAV) appears within the small base of support dictated by the feet. This is achieved to be more relevant to injury risk than asymmetry between limbs through muscle activation across the interconnected skeletal muscles (31). (22). Recreational runners with overuse injuries exhibited lower CAV asymmetry than uninjured controls, particularly in knee–ankle coupling The muscles of the biomechanical chain can be grouped by distal-to- during mid-stance and in most segment couplings during late stance, proximal segments; those of the foot and ankle, lower leg, knee and except for the pelvis and thigh (22). thigh, hip joint, pelvis, and trunk respectively. The respective muscles receive neural innervation from the lumbar and sacral plexuses (L1–S4) Increased muscle activation variability has also been observed at the as well as from the  dorsal rami of spinal nerves  and the  intercostal onset of trunk muscle fatigue, in both healthy individuals and those with nerves (Th7–Th11), (5). chronic low back pain, although the latter show less variability-likely due to avoiding painful movements (26). Similarly, prolonged muscle A biomechanical chain mechanism functions similarly to a mechanical contractions that induce fatigue tend to increase motor variability (27, 28) system composed of interconnected components designed to transmit In individuals with a history of Achilles tendon rupture, greater variability force or motion from one segment to another. In mechanical systems, in foot eversion–shank rotation coupling has been documented components like links, gears, and sprockets interact to transfer power, during 47–50% of stance-coinciding with peak ground reaction force- control motion, or transmit torque. In a biomechanical context, this indicating altered segmental control and potentially abnormal loading chain is composed of bones, joints, muscles, and their associated patterns (29). neural innervation, which work together to generate and co-ordinate movements throughout the body. Understanding motor variability is important within the framework of the biomechanical chain mechanism, as it influences how different The effectiveness of this muscular co-ordination is strongly influenced body segments co-ordinate in order to maintain an erect posture and by the human body’s bipedal posture, which repositions the BCG superimposed movement. closer to the spine directly in front of the second sacral vertebra (S2), close to the hips (11). This strategic alignment enables efficient weight MOVEMENT AND THE BIOMECHANICAL CHAIN transmission, with forces passing just ventral to the knee and ankle MECHANISM joints. The architecture of the femur, along with the alignment of the tibia, knee, and foot, ensures these structures remain closely aligned The erect posture is part of a biomechanical chain, as described by with the path of the center of gravity (COG), (32). This configuration the chain theory of body linkage, which views the body as a system of enhances balance, minimizes energy expenditure during locomotion, mechanically connected segments-from the foot to head-and this chain and supports smooth and efficient forward movement. 18 INTRODUCTION KARI HUSETH 19 Differences in walking speed and footwear, for example, have been functions together as a co-ordinated unit (30). The human biomechanical shown to influence kinematic and kinetic patterns, with some individuals chain from the metatarsal joints of the feet to the most proximal cervical adopting to a more flexed knee joint angles and higher extensor joint consists of more than 40 degrees of joint freedom movement. The moments at the knee, while others walk with a more extended knee joint sizeable number of joint freedoms enables the foot to adjust to various angles and lowerknee extensor moments (25). challenging surfaces, while at the same time allowing the biomechanical chain to function as a whole to maintain the body’s center of gravity (BCG) During running, limb-specific coordination variability (CAV) appears within the small base of support dictated by the feet. This is achieved to be more relevant to injury risk than asymmetry between limbs through muscle activation across the interconnected skeletal muscles (31). (22). Recreational runners with overuse injuries exhibited lower CAV asymmetry than uninjured controls, particularly in knee–ankle coupling The muscles of the biomechanical chain can be grouped by distal-to- during mid-stance and in most segment couplings during late stance, proximal segments; those of the foot and ankle, lower leg, knee and except for the pelvis and thigh (22). thigh, hip joint, pelvis, and trunk respectively. The respective muscles receive neural innervation from the lumbar and sacral plexuses (L1–S4) Increased muscle activation variability has also been observed at the as well as from the  dorsal rami of spinal nerves  and the  intercostal onset of trunk muscle fatigue, in both healthy individuals and those with nerves (Th7–Th11), (5). chronic low back pain, although the latter show less variability-likely due to avoiding painful movements (26). Similarly, prolonged muscle A biomechanical chain mechanism functions similarly to a mechanical contractions that induce fatigue tend to increase motor variability (27, 28) system composed of interconnected components designed to transmit In individuals with a history of Achilles tendon rupture, greater variability force or motion from one segment to another. In mechanical systems, in foot eversion–shank rotation coupling has been documented components like links, gears, and sprockets interact to transfer power, during 47–50% of stance-coinciding with peak ground reaction force- control motion, or transmit torque. In a biomechanical context, this indicating altered segmental control and potentially abnormal loading chain is composed of bones, joints, muscles, and their associated patterns (29). neural innervation, which work together to generate and co-ordinate movements throughout the body. Understanding motor variability is important within the framework of the biomechanical chain mechanism, as it influences how different The effectiveness of this muscular co-ordination is strongly influenced body segments co-ordinate in order to maintain an erect posture and by the human body’s bipedal posture, which repositions the BCG superimposed movement. closer to the spine directly in front of the second sacral vertebra (S2), close to the hips (11). This strategic alignment enables efficient weight MOVEMENT AND THE BIOMECHANICAL CHAIN transmission, with forces passing just ventral to the knee and ankle MECHANISM joints. The architecture of the femur, along with the alignment of the tibia, knee, and foot, ensures these structures remain closely aligned The erect posture is part of a biomechanical chain, as described by with the path of the center of gravity (COG), (32). This configuration the chain theory of body linkage, which views the body as a system of enhances balance, minimizes energy expenditure during locomotion, mechanically connected segments-from the foot to head-and this chain and supports smooth and efficient forward movement. 18 INTRODUCTION KARI HUSETH 19 The anatomical components in the investigated biomechanical chain present thesis, the involved muscles include the soleus, tibialis anterior, model include the skeletal bones; the phalanges, midtarsal and tarsal gastrocnemius, peroneus longus, quadriceps, sartorius, gluteus bones of the foot, tibia, fi bula, femur, pelvis, and fi nally the spine. These medius, rectus abdominis, external oblique, internal oblique/transversus bones are connected through a series of joints and ligaments, such abdominis, multifidus, and erector spinae (5), (Figure 1). as the joints of the foot and ankle: metatarsal-phalangeal (MTP), distal interphalangeal (DIP), proximal interphalangeal (PIP), tarsometatarsal, Understanding their role requires not only evaluating how segments are midtarsal, subtalar, talocrural, the knee and hip joints, sacroiliac (SI), and mechanically coupled, but also considering how experimental posture lumbar spine joints. influences muscle activation and the corresponding electromyographic (EMG) recordings (33, 34). Since neural responses are shaped by both control strategies and the mechanical context in which they occur, posture has the potential to alter muscle activation magnitude and recruitment patterns. While supine or prone positions eliminate load- bearing and postural stabilization demands, upright postures recruit trunk and lower-limb muscles in a more functionally relevant manner (35). Consequently, the methodological focus of this thesis was to compare EMG normalization procedures in supine versus standing positions, as the locomotor tasks under investigation-walking and running-are inherently performed in upright stance. BIOMECHANICS OF LOCOMOTION A central expression of the inter-muscular walking cycle co-ordination is human gait, which can be described as the transition from a posturally unstable two-foot stance into a controlled forward fall involving FIGURE 1. The biomechanical chain investigated in the present thesis, demonstrating the progressive instability, interrupted just in time by the forward foot interplay between neural components, skeletal structures, joints and muscles from the foot up making contact with the ground. This results in a continuous sequence to the trunk. of controlled forward falls, skillfully managed in the chain events to sustain balance and forward motion (36). In the biomechanical chain, forces and movements are generated and controlled by a great number of muscles, approximately 70 to 80 The walking cycle consists of two primary phases-stance (60% of the skeletal muscles from the intrinsic muscles of the foot to the deep cycle) and swing (40%) and these two phases alternate between the (31) stabilizers of the trunk. Together, these structures form a co-ordinated ipsilateral and contralateral lower extremities . As the body transitions chain that enables complex motion and effi cient power transmission from double stance (two feet touching the ground) to single leg support throughout the body. For the biomechanical chain investigated in the (one foot touching the ground), these phases work together to propel 20 INTRODUCTION KARI HUSETH 21 The anatomical components in the investigated biomechanical chain present thesis, the involved muscles include the soleus, tibialis anterior, model include the skeletal bones; the phalanges, midtarsal and tarsal gastrocnemius, peroneus longus, quadriceps, sartorius, gluteus bones of the foot, tibia, fi bula, femur, pelvis, and fi nally the spine. These medius, rectus abdominis, external oblique, internal oblique/transversus bones are connected through a series of joints and ligaments, such abdominis, multifidus, and erector spinae (5), (Figure 1). as the joints of the foot and ankle: metatarsal-phalangeal (MTP), distal interphalangeal (DIP), proximal interphalangeal (PIP), tarsometatarsal, Understanding their role requires not only evaluating how segments are midtarsal, subtalar, talocrural, the knee and hip joints, sacroiliac (SI), and mechanically coupled, but also considering how experimental posture lumbar spine joints. influences muscle activation and the corresponding electromyographic (EMG) recordings (33, 34). Since neural responses are shaped by both control strategies and the mechanical context in which they occur, posture has the potential to alter muscle activation magnitude and recruitment patterns. While supine or prone positions eliminate load- bearing and postural stabilization demands, upright postures recruit trunk and lower-limb muscles in a more functionally relevant manner (35). Consequently, the methodological focus of this thesis was to compare EMG normalization procedures in supine versus standing positions, as the locomotor tasks under investigation-walking and running-are inherently performed in upright stance. BIOMECHANICS OF LOCOMOTION A central expression of the inter-muscular walking cycle co-ordination is human gait, which can be described as the transition from a posturally unstable two-foot stance into a controlled forward fall involving FIGURE 1. The biomechanical chain investigated in the present thesis, demonstrating the progressive instability, interrupted just in time by the forward foot interplay between neural components, skeletal structures, joints and muscles from the foot up making contact with the ground. This results in a continuous sequence to the trunk. of controlled forward falls, skillfully managed in the chain events to sustain balance and forward motion (36). In the biomechanical chain, forces and movements are generated and controlled by a great number of muscles, approximately 70 to 80 The walking cycle consists of two primary phases-stance (60% of the skeletal muscles from the intrinsic muscles of the foot to the deep cycle) and swing (40%) and these two phases alternate between the (31) stabilizers of the trunk. Together, these structures form a co-ordinated ipsilateral and contralateral lower extremities . As the body transitions chain that enables complex motion and effi cient power transmission from double stance (two feet touching the ground) to single leg support throughout the body. For the biomechanical chain investigated in the (one foot touching the ground), these phases work together to propel 20 INTRODUCTION KARI HUSETH 21 the body forward in a coordinated and efficient manner. The kinematics is on foot clearance of the floor and the advancement of the limb from of the walking cycle can be further divided into three functional phases: its trailing position. In the mid-swing phase (75-87%), the ipsilateral weight acceptance, single limb support, and swing limb advancement foot is opposite the contralateral stance foot, and the swing leg’s tibia (32), (Figure 2). Each of these plays a critical role, with specific actions becomes vertical. Limb advancement continues, and foot clearance is and objectives that ensure smooth, stable, and effective locomotion now maintained. Finally, terminal swing (87-100%) occurs when the tibia in an upright position (30). The three functional phases could be further is vertical, and the foot strike is imminent. The limb has completed its subdivided as described hereunder (30). advancement and is prepared to transition into the next stance phase (Figure 3). Weight acceptance  starts with the initial contact (IC) phase, which occurs at 0-2% of the gait cycle (32). At this point, the heel rocker mechanism is WA SLS SLA activated, and the foot makes initial contact with the ground. This phase Left IC Left TO Left IC Left TO involves impact deceleration to absorb the shock generated by the LEFT STANCE PHASE LEFT SWING PHASE LEFT STANCE PHASE foot strike. The next phase, the loading response, spans from 2-12% of the gait cycle. During this time period, the contralateral limb is lifted DS DS for swing, and the body absorbs the shock from impact. The loading RIGHT SWING PHASE RIGHT STANCE PHASE RIGHT SWING PHASE response also serves to provide initial limb stability and preserve Right IC Right TO Right IC forward propulsion, ensuring continued progress in movement (32). Time Single Limb Support starts with the lifting of the contralateral foot for FIGURE 2. Schematic illustration of the stance and swing phases of gait, with the reciprocal the swing phase. The midstance phase, which occurs between 12- action between left and right limb. WA = weight acceptance, SLS = Single Limb Support, SLA = Swing Limb Advancement, IC = initial contact, TO = toe-off, DS = double stance. 31% of the gait cycle, involves progression over the stationary foot. Stability in both the limb and trunk is crucial here to maintain balance. The terminal stance, which occurs from 31-50% of the gait cycle, is The body’s subdivisions play a role in maintaining postural integrity and marked by the heel rise while the contralateral foot is in contact with facilitating movement. The passenger unit (head, arms, and trunk, or the ground. During this phase, the body continues to progress beyond HAT) comprises approximately 70% of the body weight and maintains the supporting foot, and limb and trunk stability is once again the key to postural integrity throughout the gait cycle. The center of mass (COM) successful movement. is located approximately one-third of the distance between the hip joint center and the shoulder joint center, at the level of the 10th thoracic Swing Limb Advancement includes several phases that work together vertebra (Th10). Minimizing postural changes from the pelvis to the to advance the limb through the cycle. The pre-swing phase (50-62%) hip is essential for smooth movement. While arm swing is not strictly is marked by toe-off and the initial contact of the contralateral limb. essential, it helps balance and aids in the overall efficiency of walking. This phase involves positioning the limb for swing and accelerating progression. The initial swing that occurs between 62-75% of the gait cycle, starts when the ipsilateral foot is lifted from the floor, and the contralateral limb is in the stance phase. During this phase, the focus 22 INTRODUCTION KARI HUSETH 23 the body forward in a coordinated and efficient manner. The kinematics is on foot clearance of the floor and the advancement of the limb from of the walking cycle can be further divided into three functional phases: its trailing position. In the mid-swing phase (75-87%), the ipsilateral weight acceptance, single limb support, and swing limb advancement foot is opposite the contralateral stance foot, and the swing leg’s tibia (32), (Figure 2). Each of these plays a critical role, with specific actions becomes vertical. Limb advancement continues, and foot clearance is and objectives that ensure smooth, stable, and effective locomotion now maintained. Finally, terminal swing (87-100%) occurs when the tibia in an upright position (30). The three functional phases could be further is vertical, and the foot strike is imminent. The limb has completed its subdivided as described hereunder (30). advancement and is prepared to transition into the next stance phase (Figure 3). Weight acceptance  starts with the initial contact (IC) phase, which occurs at 0-2% of the gait cycle (32). At this point, the heel rocker mechanism is WA SLS SLA activated, and the foot makes initial contact with the ground. This phase Left IC Left TO Left IC Left TO involves impact deceleration to absorb the shock generated by the LEFT STANCE PHASE LEFT SWING PHASE LEFT STANCE PHASE foot strike. The next phase, the loading response, spans from 2-12% of the gait cycle. During this time period, the contralateral limb is lifted DS DS for swing, and the body absorbs the shock from impact. The loading RIGHT SWING PHASE RIGHT STANCE PHASE RIGHT SWING PHASE response also serves to provide initial limb stability and preserve Right IC Right TO Right IC forward propulsion, ensuring continued progress in movement (32). Time Single Limb Support starts with the lifting of the contralateral foot for FIGURE 2. Schematic illustration of the stance and swing phases of gait, with the reciprocal the swing phase. The midstance phase, which occurs between 12- action between left and right limb. WA = weight acceptance, SLS = Single Limb Support, SLA = Swing Limb Advancement, IC = initial contact, TO = toe-off, DS = double stance. 31% of the gait cycle, involves progression over the stationary foot. Stability in both the limb and trunk is crucial here to maintain balance. The terminal stance, which occurs from 31-50% of the gait cycle, is The body’s subdivisions play a role in maintaining postural integrity and marked by the heel rise while the contralateral foot is in contact with facilitating movement. The passenger unit (head, arms, and trunk, or the ground. During this phase, the body continues to progress beyond HAT) comprises approximately 70% of the body weight and maintains the supporting foot, and limb and trunk stability is once again the key to postural integrity throughout the gait cycle. The center of mass (COM) successful movement. is located approximately one-third of the distance between the hip joint center and the shoulder joint center, at the level of the 10th thoracic Swing Limb Advancement includes several phases that work together vertebra (Th10). Minimizing postural changes from the pelvis to the to advance the limb through the cycle. The pre-swing phase (50-62%) hip is essential for smooth movement. While arm swing is not strictly is marked by toe-off and the initial contact of the contralateral limb. essential, it helps balance and aids in the overall efficiency of walking. This phase involves positioning the limb for swing and accelerating progression. The initial swing that occurs between 62-75% of the gait cycle, starts when the ipsilateral foot is lifted from the floor, and the contralateral limb is in the stance phase. During this phase, the focus 22 INTRODUCTION KARI HUSETH 23 TABLE 1. Muscles and joint/action involved in the walking cycle of the ipsilateral limb. Gait phases Joint Movement Muscles Initial contact hip FLEX iliopsoas knee EXT quadriceps ankle/foot DF tibialis anterior, extensor digitorum longus and brevis, extensor hallucis Loading response hip EXT gluteus maximus IC MS TO Flat foot knee extension EXT quadriceps STANCE SWING ankle/foot Midstance hip EXT gluteus maximus, hamstring FIGURE 3. The walking cycle illustrated for the left leg. The stance phase includes initial contact (IC), mid-stance (MS), and toe-off (TO). The swing phase follows, defi ned as the portion of the gait knee work EXT hamstring in antagonism/synergism with quadriceps cycle during which the foot is off the ground and the leg swings forward in preparation for the next step-from toe-off to the subsequent initial contact. ankle/foot DF tibialis anterior Heel-off hip ext EXT gluteus maximus, hamstring Just before end of knee ext EXT quadriceps double support The locomotor unit, which includes both lower extremities and the ankle/foot PF triceps surae , toe flex pelvis, is critical for movement. This unit includes multiple articulations, Toe-off/pre-swing hip EXT gluteus maximus, hamstring such as the lumbosacral joint, hip joints, knees, ankles, subtalar joints, knee EXT quadriceps, hamstring and metatarsophalangeal (MTP) joints, all working together as a ankle/foot PF triceps surae, toes flex,flexor hallux longus smooth and well-balanced chain to propel the body forward. In terms Early swing hip FLEX iliopsoas of muscle function, the pelvis is an essential part of the locomotor unit. Single support knee FLEX hamstring It advances during the swing phase and undergoes backward rotation from other limb in the terminal stance, transitioning to forward rotation in the terminal ankle/foot DF tibialis anterior Mid-swing hip FLEX iliopsoas swing. This rotation facilitates effi cient progression and supports the Forward movement knee EXT quadriceps body’s stability during gait. of swing limb ankle/foot DF tibialis anterior, extensor digitorum longus and brevis, extensor halluces Terminal contact hip FLEX iliopsoas Swing limb off knee EXT quadriceps the ground ankle/foot DF tibialis anterior Early advances hip FLEX iliopsoas of leading limb- preloading knee FLEX hamstring ankle/foot DF tibialis anterior, extensor digitorum longus and brevis, extensor halluces Decription of joints/joint actions and corresponding muscles during the different phases of the walking cycle. Abbreviations of movements during the walking cycle: EXT = extention, FLEX = flexion, DF = dorsiflexion, PF = plantar flexion. 24 INTRODUCTION KARI HUSETH 25 TABLE 1. Muscles and joint/action involved in the walking cycle of the ipsilateral limb. Gait phases Joint Movement Muscles Initial contact hip FLEX iliopsoas knee EXT quadriceps ankle/foot DF tibialis anterior, extensor digitorum longus and brevis, extensor hallucis Loading response hip EXT gluteus maximus IC MS TO Flat foot knee extension EXT quadriceps STANCE SWING ankle/foot Midstance hip EXT gluteus maximus, hamstring FIGURE 3. The walking cycle illustrated for the left leg. The stance phase includes initial contact (IC), mid-stance (MS), and toe-off (TO). The swing phase follows, defi ned as the portion of the gait knee work EXT hamstring in antagonism/synergism with quadriceps cycle during which the foot is off the ground and the leg swings forward in preparation for the next step-from toe-off to the subsequent initial contact. ankle/foot DF tibialis anterior Heel-off hip ext EXT gluteus maximus, hamstring Just before end of knee ext EXT quadriceps double support The locomotor unit, which includes both lower extremities and the ankle/foot PF triceps surae , toe flex pelvis, is critical for movement. This unit includes multiple articulations, Toe-off/pre-swing hip EXT gluteus maximus, hamstring such as the lumbosacral joint, hip joints, knees, ankles, subtalar joints, knee EXT quadriceps, hamstring and metatarsophalangeal (MTP) joints, all working together as a ankle/foot PF triceps surae, toes flex,flexor hallux longus smooth and well-balanced chain to propel the body forward. In terms Early swing hip FLEX iliopsoas of muscle function, the pelvis is an essential part of the locomotor unit. Single support knee FLEX hamstring It advances during the swing phase and undergoes backward rotation from other limb in the terminal stance, transitioning to forward rotation in the terminal ankle/foot DF tibialis anterior Mid-swing hip FLEX iliopsoas swing. This rotation facilitates effi cient progression and supports the Forward movement knee EXT quadriceps body’s stability during gait. of swing limb ankle/foot DF tibialis anterior, extensor digitorum longus and brevis, extensor halluces Terminal contact hip FLEX iliopsoas Swing limb off knee EXT quadriceps the ground ankle/foot DF tibialis anterior Early advances hip FLEX iliopsoas of leading limb- preloading knee FLEX hamstring ankle/foot DF tibialis anterior, extensor digitorum longus and brevis, extensor halluces Decription of joints/joint actions and corresponding muscles during the different phases of the walking cycle. Abbreviations of movements during the walking cycle: EXT = extention, FLEX = flexion, DF = dorsiflexion, PF = plantar flexion. 24 INTRODUCTION KARI HUSETH 25 Each phase and body subdivision is integral to the smooth execution of while the swing phase makes up 40% (40). In contrast, running features the gait cycle, highlighting the complexity and co-ordination required a stance phase of approximately 40%, characterized by a more for efficient locomotion (36), (Table 1). pronounced push-off , and a swing phase of 60%, which includes a fl ight phase, where both feet are off the ground. This fl ight phase is a unique The inverted pendulum theory of walking describes how the body moves feature of running that does not occur during walking (31). over the stance leg in a way that resembles an inverted pendulum (37). During the single support phase of gait, the stance leg remains relatively Ground reaction forces also vary between the two activities (Figure 4). straight, while the body’s center of mass vaults over it in an arc-like motion. During walking, the ground reaction force is approximately 1.2 times This “rocking” movement allows for efficient energy exchange; potential the body weight, with peak forces during initial contact and push-off energy is converted into kinetic energy and then back again, minimizing (1). Running, however, generates greater forces, reaching 2-3 times the the muscular work required for forward progression. This model helps body weight during foot strike. This increased force during running is explain the characteristic rise and fall of the COM during walking and also related to the higher speed and the need for more propulsion and highlights the passive, energy-conserving nature of human gait (38). shock absorption during the stance foot strike (39). The bouncing principle of running is described by the spring-mass model, in which the body behaves like a bouncing ball or a mass supported by Walking: IC Running: IC a spring (39). One expression of this coordination is human gait, which can be described as the transition from a posturally unstable two-foot stance into a controlled forward fall involving progressive instability. During each step, the leg compresses upon ground contact, storing elastic energy in muscles, tendons- especially the Achilles tendon-and other connective tissues. Given its critical role in energy storage and release during the stance and push-off phases, the Achilles tendon is a key structure for efficient walking and running. For this reason, the present thesis focuses on the Achilles tendon to better understand its function and compensatory mechanisms in locomotion following injury. This stored energy in the Achilles tendon is then released during push-off, propelling the body forward. Unlike walking, where the body vaults over the rigid/straight leg (inverted pendulum), running involves a cyclical exchange between kinetic and elastic potential energies enabling efficient forward motion with minimal energy loss (40). FIGURE 4. The green curves illustrate the path of the ground reaction forces (GRFs) throughout When walking is compared with running, the phases of movement differ stance. The red arrow indicate the direction and magnitude of the GRF at intial contact (IC). The significantly (41). In walking, the stance phase makes up approximately yellow stick fi gures trace the movement of the body segments, following the motion of the ankle, knee, and hip joints. Compared with walking, running produces GRFs of greater magnitude and 60% of the cycle, consisting of initial contact, midstance, and toe-off, diff erent orientation. 26 INTRODUCTION KARI HUSETH 27 Each phase and body subdivision is integral to the smooth execution of while the swing phase makes up 40% (40). In contrast, running features the gait cycle, highlighting the complexity and co-ordination required a stance phase of approximately 40%, characterized by a more for efficient locomotion (36), (Table 1). pronounced push-off , and a swing phase of 60%, which includes a fl ight phase, where both feet are off the ground. This fl ight phase is a unique The inverted pendulum theory of walking describes how the body moves feature of running that does not occur during walking (31). over the stance leg in a way that resembles an inverted pendulum (37). During the single support phase of gait, the stance leg remains relatively Ground reaction forces also vary between the two activities (Figure 4). straight, while the body’s center of mass vaults over it in an arc-like motion. During walking, the ground reaction force is approximately 1.2 times This “rocking” movement allows for efficient energy exchange; potential the body weight, with peak forces during initial contact and push-off energy is converted into kinetic energy and then back again, minimizing (1). Running, however, generates greater forces, reaching 2-3 times the the muscular work required for forward progression. This model helps body weight during foot strike. This increased force during running is explain the characteristic rise and fall of the COM during walking and also related to the higher speed and the need for more propulsion and highlights the passive, energy-conserving nature of human gait (38). shock absorption during the stance foot strike (39). The bouncing principle of running is described by the spring-mass model, in which the body behaves like a bouncing ball or a mass supported by Walking: IC Running: IC a spring (39). One expression of this coordination is human gait, which can be described as the transition from a posturally unstable two-foot stance into a controlled forward fall involving progressive instability. During each step, the leg compresses upon ground contact, storing elastic energy in muscles, tendons- especially the Achilles tendon-and other connective tissues. Given its critical role in energy storage and release during the stance and push-off phases, the Achilles tendon is a key structure for efficient walking and running. For this reason, the present thesis focuses on the Achilles tendon to better understand its function and compensatory mechanisms in locomotion following injury. This stored energy in the Achilles tendon is then released during push-off, propelling the body forward. Unlike walking, where the body vaults over the rigid/straight leg (inverted pendulum), running involves a cyclical exchange between kinetic and elastic potential energies enabling efficient forward motion with minimal energy loss (40). FIGURE 4. The green curves illustrate the path of the ground reaction forces (GRFs) throughout When walking is compared with running, the phases of movement differ stance. The red arrow indicate the direction and magnitude of the GRF at intial contact (IC). The significantly (41). In walking, the stance phase makes up approximately yellow stick fi gures trace the movement of the body segments, following the motion of the ankle, knee, and hip joints. Compared with walking, running produces GRFs of greater magnitude and 60% of the cycle, consisting of initial contact, midstance, and toe-off, diff erent orientation. 26 INTRODUCTION KARI HUSETH 27 Stride length and cadence further differentiate walking from running. speed at which these activities occur is another major diff erence, while Walking involves shorter, lower strides, while running is characterized walking is typically performed at moderate speeds, running allows for by longer strides that are directly correlated with increased speed much higher speeds, due to longer strides and faster cadence (Figure 5). (42). As for joint angles and motion, walking involves approximately 60 degrees of knee flexion during the swing phase, with a smaller range of plantar flexion (PF) and dorsiflexion (DF), (42). Running, on the other hand, involves greater knee flexion, ranging from 90 to 120 degrees, and a larger range of PF and DF as the body needs more flexibility and mobility STANCE FLOAT SWING FLOAT to generate force and propulsion (42). FIGURE 5. The running cycle, illustrated for the single stance phase (foot contact), fl ight phase (fl oat), swing phase (forward leg movement), followed by a second fl ight phase before the Muscle activation is also more intense during running, while, during subsequent foot strike. Unlike walking, running includes two distinct fl ight phases during which walking, muscle activation is moderate and rhythmic, with the quad- neither foot is in contact with the ground. riceps, hamstrings, gluteii, and shank muscles being activated to a lesser extent (42). During running, however, muscle activation is greater than during walking, particularly in the quadriceps, hamstrings, and LOCOMOTION AND FEET KINEMATICS shank muscles, as they play key roles in absorbing impact, generating propulsion, and stabilizing the joints due to the higher forces involved. The foot adapted to locomotion, acts as a lever adding propulsive This increased muscle activity in running leads to a greater metabolic forces to the lower limb (43). demand, making running more energy-intensive than walking. Interest- The foot is a complex anatomical structure, composed of 26 bones ingly, running is therefore metabolically more efficient than walking at and 33 joints, which together allow for a wide range of motion and higher speeds, despite its higher energy expenditure (42). adaptability. Its design enables a dynamic shift between fl exibility and Foot strike patterns are another distinction between the two activities. rigidity, largely due to the spring-like function of the foot arches (31). These Walking typically follows a heel-to-toe pattern, while running can have a arches allow the foot to absorb shock and adapt to uneven terrain when more varied foot strike depending on the individual running technique. fl exible and then to provide a solid stiff er lever for propulsion during Postural control is also different; during walking, the body remains gait. This adaptability is closely linked to transitions between pronated upright, with the COM staying relatively stable. During running on the and supinated positions. Movement within the ankle-foot complex other hand, there is a slight forward lean, and the COM moves more occurs across multiple planes and axes; dorsifl exion and plantarfl exion dynamically due to the flight phase. take place in the sagittal plane, rotating around a transverse axis that runs from the lateral malleolus through the body of the talus to the Impact and load distribution also differ significantly between walking and medial malleolus (30). Inversion and eversion occur in the frontal plane running. During walking, the impact is evenly distributed, with relatively around a longitudinal axis aligned with the length of the foot; inversion low impact on the knees and hips. Running, however, involves greater involves the plantar surface turning toward the midline, while eversion impact on the ankles, knees, and hips, which is why proper technique is the opposite. Adduction and abduction occur in the transverse plane, and muscle activation are important to minimize the injury risk. Lastly, the rotating around a vertical axis; abduction involves the distal aspect of a 28 INTRODUCTION KARI HUSETH 29 Stride length and cadence further differentiate walking from running. speed at which these activities occur is another major diff erence, while Walking involves shorter, lower strides, while running is characterized walking is typically performed at moderate speeds, running allows for by longer strides that are directly correlated with increased speed much higher speeds, due to longer strides and faster cadence (Figure 5). (42). As for joint angles and motion, walking involves approximately 60 degrees of knee flexion during the swing phase, with a smaller range of plantar flexion (PF) and dorsiflexion (DF), (42). Running, on the other hand, involves greater knee flexion, ranging from 90 to 120 degrees, and a larger range of PF and DF as the body needs more flexibility and mobility STANCE FLOAT SWING FLOAT to generate force and propulsion (42). FIGURE 5. The running cycle, illustrated for the single stance phase (foot contact), fl ight phase (fl oat), swing phase (forward leg movement), followed by a second fl ight phase before the Muscle activation is also more intense during running, while, during subsequent foot strike. Unlike walking, running includes two distinct fl ight phases during which walking, muscle activation is moderate and rhythmic, with the quad- neither foot is in contact with the ground. riceps, hamstrings, gluteii, and shank muscles being activated to a lesser extent (42). During running, however, muscle activation is greater than during walking, particularly in the quadriceps, hamstrings, and LOCOMOTION AND FEET KINEMATICS shank muscles, as they play key roles in absorbing impact, generating propulsion, and stabilizing the joints due to the higher forces involved. The foot adapted to locomotion, acts as a lever adding propulsive This increased muscle activity in running leads to a greater metabolic forces to the lower limb (43). demand, making running more energy-intensive than walking. Interest- The foot is a complex anatomical structure, composed of 26 bones ingly, running is therefore metabolically more efficient than walking at and 33 joints, which together allow for a wide range of motion and higher speeds, despite its higher energy expenditure (42). adaptability. Its design enables a dynamic shift between fl exibility and Foot strike patterns are another distinction between the two activities. rigidity, largely due to the spring-like function of the foot arches (31). These Walking typically follows a heel-to-toe pattern, while running can have a arches allow the foot to absorb shock and adapt to uneven terrain when more varied foot strike depending on the individual running technique. fl exible and then to provide a solid stiff er lever for propulsion during Postural control is also different; during walking, the body remains gait. This adaptability is closely linked to transitions between pronated upright, with the COM staying relatively stable. During running on the and supinated positions. Movement within the ankle-foot complex other hand, there is a slight forward lean, and the COM moves more occurs across multiple planes and axes; dorsifl exion and plantarfl exion dynamically due to the flight phase. take place in the sagittal plane, rotating around a transverse axis that runs from the lateral malleolus through the body of the talus to the Impact and load distribution also differ significantly between walking and medial malleolus (30). Inversion and eversion occur in the frontal plane running. During walking, the impact is evenly distributed, with relatively around a longitudinal axis aligned with the length of the foot; inversion low impact on the knees and hips. Running, however, involves greater involves the plantar surface turning toward the midline, while eversion impact on the ankles, knees, and hips, which is why proper technique is the opposite. Adduction and abduction occur in the transverse plane, and muscle activation are important to minimize the injury risk. Lastly, the rotating around a vertical axis; abduction involves the distal aspect of a 28 INTRODUCTION KARI HUSETH 29 segment moving away from the midline of the foot, whereas adduction The range of motion for the foot and ankle complex includes 20° of brings it closer to the midline (36), (Figure 6). dorsifl exion, 50° of plantarfl exion, 20° of eversion, 10° of inversion, 15° of abduction, 15° of adduction, 35° of supination, and 20° of pronation (31, 32, 45). FIGURE 6. The oblique axis of ankle motion at the subtalar and midtarsal joints, along which pronation (dorsifl exion, eversion, abduction) and supination (plantarfl exion, inversion, adduction) FIGURE 7. Sagittal plane motion for ankle–foot complex, depicting dorsifl exion, plantarfl exion occur as coordinated triplanar movements. along the x-axis, frontal plane motion along the y-axis, and transverse plane motion along the z-axis. Supination and pronation are fundamental foot movements that occur in response to the dynamic demands of locomotion. Supination is the Through the talus, the most distal bone of the lower leg, the weight from combination of adduction, plantarfl exion, and inversion, which results the body is transferred to the entire foot (36). This weight is absorbed with the foot becoming more rigid, facilitating a stable push-off . In and cushioned by the pronation movement of the foot. Arguably, when contrast, pronation involves abduction, dorsifl exion, and eversion, the foot moves into pronation during midstance the tibia and femur allowing the foot to absorb shock and adapt to the surface during weight rotate internally, and consequently the pelvis on the same side rotates acceptance. These movements are governed by triplane motion, with anteriorly, causing a transient increment in lumbar lordosis (31, 46). an oblique axis running in an angular direction, enabling motion across the frontal, transverse, and sagittal planes. This coordinated sequence highlights the kinematic chain in action, where movement at one joint infl uences motion at other joints more During the gait cycle the foot will be in a neutral to slightly supinated proximally in the chain. In the context of locomotion, the role of the position during heel strike and in the phase of initial ground contact, biomechanical chain is particularly evident at the ankle, where agonist while moving into pronation during the midstance phase, and fi nally and antagonist muscle pairs control dorsifl exion and plantarfl exion moving into supination during the late terminal stance and pre-swing (44). respectively, each contributing to distinct phases of the gait cycle (31, 30 INTRODUCTION KARI HUSETH 31 segment moving away from the midline of the foot, whereas adduction The range of motion for the foot and ankle complex includes 20° of brings it closer to the midline (36), (Figure 6). dorsifl exion, 50° of plantarfl exion, 20° of eversion, 10° of inversion, 15° of abduction, 15° of adduction, 35° of supination, and 20° of pronation (31, 32, 45). FIGURE 6. The oblique axis of ankle motion at the subtalar and midtarsal joints, along which pronation (dorsifl exion, eversion, abduction) and supination (plantarfl exion, inversion, adduction) FIGURE 7. Sagittal plane motion for ankle–foot complex, depicting dorsifl exion, plantarfl exion occur as coordinated triplanar movements. along the x-axis, frontal plane motion along the y-axis, and transverse plane motion along the z-axis. Supination and pronation are fundamental foot movements that occur in response to the dynamic demands of locomotion. Supination is the Through the talus, the most distal bone of the lower leg, the weight from combination of adduction, plantarfl exion, and inversion, which results the body is transferred to the entire foot (36). This weight is absorbed with the foot becoming more rigid, facilitating a stable push-off . In and cushioned by the pronation movement of the foot. Arguably, when contrast, pronation involves abduction, dorsifl exion, and eversion, the foot moves into pronation during midstance the tibia and femur allowing the foot to absorb shock and adapt to the surface during weight rotate internally, and consequently the pelvis on the same side rotates acceptance. These movements are governed by triplane motion, with anteriorly, causing a transient increment in lumbar lordosis (31, 46). an oblique axis running in an angular direction, enabling motion across the frontal, transverse, and sagittal planes. This coordinated sequence highlights the kinematic chain in action, where movement at one joint infl uences motion at other joints more During the gait cycle the foot will be in a neutral to slightly supinated proximally in the chain. In the context of locomotion, the role of the position during heel strike and in the phase of initial ground contact, biomechanical chain is particularly evident at the ankle, where agonist while moving into pronation during the midstance phase, and fi nally and antagonist muscle pairs control dorsifl exion and plantarfl exion moving into supination during the late terminal stance and pre-swing (44). respectively, each contributing to distinct phases of the gait cycle (31, 30 INTRODUCTION KARI HUSETH 31 47), (Figure 7). Dorsiflexors, such as the tibialis anterior, are active during the head and proximal shaft of the fi bula, the soleal line, and the middle the initial contact and loading response to control foot placement, while third of the medial border of the tibia. Unlike the gastrocnemius muscle, plantar flexors, like the gastrocnemius and soleus, are key muscles the soleus muscle is a monoarticular muscle, acting on the ankle joint during the push-off to generate forward propulsion (32). When the only. Although mostly covered by the gastrocnemius, the soleus muscle Achilles tendon is injured, the efficiency of this system is potentinally becomes visible and more easily accessible just below the mid-calf on compromised (48, 49). The inability to effectively plantarflex the foot both the medial and lateral sides. Both muscles are innervated by the will then disrupt the timing and force of push-off (50), which in turn will tibial nerve derived from spinal nerve roots S1 and S2 (45). affect the mechanics of the entire kinematic chain. This could lead to compensatory movements at the knee, hip, and pelvis, and potentially exacerbate issues such as changed, i.e. either increased or decreased lumbar lordosis and placing additional strain on the lower back and postural alignment. LOCOMOTION AND THE ACHILLES TENDON The Achilles tendon is among the largest and strongest tendons in the human body, playing a critical role in bipedal locomotion (51, 52). Evolutionarily optimized for both repetitive loading and explosive movement, it transmits forces from the triceps surae-comprising the gastrocnemius medialis, gastrocnemius lateralis, and soleus muscles- into powerful ankle plantarflexion (53), (Figure 8). The gastrocnemius muscle has two distinct heads-medial and lateral. The medial head, which is larger, originates from the popliteal surface of the femur just above the medial femoral condyle. The lateral head arises from the upper and posterior surface of the lateral femoral condyle and the distal part of the lateral supracondylar line of the femur. Both heads are also interviened with fibers from the subjacent areas of the knee joint capsule. They remain separate as they descend until they converge into a broad aponeurosis. The gastrocnemius is a biarticular muscle, crossing both the knee and ankle joints, and therefore contributes to movement at both levels. As it moves caudally, the gastrocnemius muscles join with FIGURE 8. The triceps surae of the right leg, comprising the medial and lateral gastrocnemius the tendon of the soleus muscle on its deep surface to form the Achilles and the soleus, arises from distinct sites: the gastrocnemius from the medial and lateral femoral tendon. The soleus muscle, a broad and flat muscle that lies deep to condyles, and the soleus from the posterior surface of the tibia and fi bula. These muscles converge into the Achilles tendon, which inserts onto the calcaneus. The right side of the the gastrocnemius muscle, originates from the posterior surface of illustration does also depict the rotation of the Achilles tendon. 32 INTRODUCTION KARI HUSETH 33 47), (Figure 7). Dorsiflexors, such as the tibialis anterior, are active during the head and proximal shaft of the fi bula, the soleal line, and the middle the initial contact and loading response to control foot placement, while third of the medial border of the tibia. Unlike the gastrocnemius muscle, plantar flexors, like the gastrocnemius and soleus, are key muscles the soleus muscle is a monoarticular muscle, acting on the ankle joint during the push-off to generate forward propulsion (32). When the only. Although mostly covered by the gastrocnemius, the soleus muscle Achilles tendon is injured, the efficiency of this system is potentinally becomes visible and more easily accessible just below the mid-calf on compromised (48, 49). The inability to effectively plantarflex the foot both the medial and lateral sides. Both muscles are innervated by the will then disrupt the timing and force of push-off (50), which in turn will tibial nerve derived from spinal nerve roots S1 and S2 (45). affect the mechanics of the entire kinematic chain. This could lead to compensatory movements at the knee, hip, and pelvis, and potentially exacerbate issues such as changed, i.e. either increased or decreased lumbar lordosis and placing additional strain on the lower back and postural alignment. LOCOMOTION AND THE ACHILLES TENDON The Achilles tendon is among the largest and strongest tendons in the human body, playing a critical role in bipedal locomotion (51, 52). Evolutionarily optimized for both repetitive loading and explosive movement, it transmits forces from the triceps surae-comprising the gastrocnemius medialis, gastrocnemius lateralis, and soleus muscles- into powerful ankle plantarflexion (53), (Figure 8). The gastrocnemius muscle has two distinct heads-medial and lateral. The medial head, which is larger, originates from the popliteal surface of the femur just above the medial femoral condyle. The lateral head arises from the upper and posterior surface of the lateral femoral condyle and the distal part of the lateral supracondylar line of the femur. Both heads are also interviened with fibers from the subjacent areas of the knee joint capsule. They remain separate as they descend until they converge into a broad aponeurosis. The gastrocnemius is a biarticular muscle, crossing both the knee and ankle joints, and therefore contributes to movement at both levels. As it moves caudally, the gastrocnemius muscles join with FIGURE 8. The triceps surae of the right leg, comprising the medial and lateral gastrocnemius the tendon of the soleus muscle on its deep surface to form the Achilles and the soleus, arises from distinct sites: the gastrocnemius from the medial and lateral femoral tendon. The soleus muscle, a broad and flat muscle that lies deep to condyles, and the soleus from the posterior surface of the tibia and fi bula. These muscles converge into the Achilles tendon, which inserts onto the calcaneus. The right side of the the gastrocnemius muscle, originates from the posterior surface of illustration does also depict the rotation of the Achilles tendon. 32 INTRODUCTION KARI HUSETH 33 This musculotendinous unit functions as an energy-storing spring: the has been reported (68). This trend is accompanied by an increase in the tendon elongates under load during stance and recoils during push-off, median age of patients who sustain an ATR, from 44 to 50 years between which leads to enhanced propulsion and less metabolic cost of movement 2001 and 2012, and also with a notable rise among individuals over 60 (2, 54, 55). During walking and running, tendon loads range from 2.7 to 7.7 years of age (66-68). Recent studies also report a bimodal age distribution, times body weight, depending on the speed and task intensity (56). with incidence peaks in middle age and in older adults (69). Vosseller et al., reported a strong male predominance, with a male-to-female ratio Structurally, the Achilles tendon demonstrates considerable mechanical of 5.4:1 (70). Similarly, Hartman et al., in their retrospective study, found resilience. It is composed of fascicles with a spiraling orientation and a that males accounted for almost 82% of all ATR (71) and the median distinctive 90° twist from the myotendinous junction to the calcaneal age of rupture has shifted upward, most probably reflecting increased insertion (57-59). This anatomical configuration, in conjunction with participation in recreational sports among older individuals. aponeurotic integration of the triceps surae, enables multidirectional load distribution and efficient force transfer, especially at the ankle joint Irrespective of the treatment protocol (surgical or non-surgical), level (51, 60). The tendon’s mechanical properties are tightly coupled to persistent functional deficits are commonly observed following the neuromuscular control strategies that regulate stiffness, compliance, Acilles tendon injury (72, 73). Tendon elongation is strongly associated and energy absorption during the entire gait cycle (54, 61). with long-term reduction in plantarflexor strength, heel-rise height, and altered ankle joint kinetics (74-76). Recent studies have further Although structurally well-adapted to handle high loads, the Achilles highlighted changes in tendon stiffness (77) and muscle architecture, tendon remains particularly vulnerable to injury as a result of the such as shortened medial gastrocnemius fascicles (78), which, indicates substantial and repetitive mechanical demands it encounters during remodeling responses within the triceps surae complex (71). activity, especially under eccentric loading conditions (62, 63), (Figure 9). Achilles tendon rupture (ATR) typically occurs during forceful dorsiflexion Compensatory neuromuscular adaptations are frequently observed of a plantarflexed foot or during sudden acceleration or deceleration after an ATR. Increased reliance on the lateral gastrocnemius and soleus movements, such as jumping or directional changes, for instance during is often reported, possibly reflecting reduced activation or hypotrophy sports activities (62, 63). Contributing factors often include neuromuscular of the medial gastrocnemius (79, 80). Anatomical remodeling, including fatigue, inadequate preparatory muscle activation, and age-related fascicle length adaptation, may, however, allow the muscle-tendon unit to or subclinical degenerative changes, such as disorganized collagen function effectively under altered mechanical conditions (78). structure, neovascularization, and microruptures. These changes often occur in the relatively hypovascular midportion of the tendon, a region At the joint level, ATR disrupts the coordinated distribution of mechanical particularly vulnerable to age-related degeneration (64, 65). work. Several studies have shown reduced ankle power and increased reliance on knee and hip extensors during walking, jogging, and dynamic The prevalence of ATR has shown a gradual increase over recent tasks, such as jumping and/or landing (49, 81). These findings could align decades across several Nordic countries. In Denmark, the incidence with the concept of the biomechanical chain and the broader chain rose from 26.9 per 100,000 person-years in 1994 to 31.7 in 2013 (66), theory of body linkage, in which impairments at the foot or ankle level while in Sweden it increased from 34.3 in 2017 to 41.7 in 2021 (67). may influence more proximal segments in order to maintain global Similarly, in Finland a rise from 17.3 to 32.3 per 100,000 person-years locomotor function. 34 INTRODUCTION KARI HUSETH 35 This musculotendinous unit functions as an energy-storing spring: the has been reported (68). This trend is accompanied by an increase in the tendon elongates under load during stance and recoils during push-off, median age of patients who sustain an ATR, from 44 to 50 years between which leads to enhanced propulsion and less metabolic cost of movement 2001 and 2012, and also with a notable rise among individuals over 60 (2, 54, 55). During walking and running, tendon loads range from 2.7 to 7.7 years of age (66-68). Recent studies also report a bimodal age distribution, times body weight, depending on the speed and task intensity (56). with incidence peaks in middle age and in older adults (69). Vosseller et al., reported a strong male predominance, with a male-to-female ratio Structurally, the Achilles tendon demonstrates considerable mechanical of 5.4:1 (70). Similarly, Hartman et al., in their retrospective study, found resilience. It is composed of fascicles with a spiraling orientation and a that males accounted for almost 82% of all ATR (71) and the median distinctive 90° twist from the myotendinous junction to the calcaneal age of rupture has shifted upward, most probably reflecting increased insertion (57-59). This anatomical configuration, in conjunction with participation in recreational sports among older individuals. aponeurotic integration of the triceps surae, enables multidirectional load distribution and efficient force transfer, especially at the ankle joint Irrespective of the treatment protocol (surgical or non-surgical), level (51, 60). The tendon’s mechanical properties are tightly coupled to persistent functional deficits are commonly observed following the neuromuscular control strategies that regulate stiffness, compliance, Acilles tendon injury (72, 73). Tendon elongation is strongly associated and energy absorption during the entire gait cycle (54, 61). with long-term reduction in plantarflexor strength, heel-rise height, and altered ankle joint kinetics (74-76). Recent studies have further Although structurally well-adapted to handle high loads, the Achilles highlighted changes in tendon stiffness (77) and muscle architecture, tendon remains particularly vulnerable to injury as a result of the such as shortened medial gastrocnemius fascicles (78), which, indicates substantial and repetitive mechanical demands it encounters during remodeling responses within the triceps surae complex (71). activity, especially under eccentric loading conditions (62, 63), (Figure 9). Achilles tendon rupture (ATR) typically occurs during forceful dorsiflexion Compensatory neuromuscular adaptations are frequently observed of a plantarflexed foot or during sudden acceleration or deceleration after an ATR. Increased reliance on the lateral gastrocnemius and soleus movements, such as jumping or directional changes, for instance during is often reported, possibly reflecting reduced activation or hypotrophy sports activities (62, 63). Contributing factors often include neuromuscular of the medial gastrocnemius (79, 80). Anatomical remodeling, including fatigue, inadequate preparatory muscle activation, and age-related fascicle length adaptation, may, however, allow the muscle-tendon unit to or subclinical degenerative changes, such as disorganized collagen function effectively under altered mechanical conditions (78). structure, neovascularization, and microruptures. These changes often occur in the relatively hypovascular midportion of the tendon, a region At the joint level, ATR disrupts the coordinated distribution of mechanical particularly vulnerable to age-related degeneration (64, 65). work. Several studies have shown reduced ankle power and increased reliance on knee and hip extensors during walking, jogging, and dynamic The prevalence of ATR has shown a gradual increase over recent tasks, such as jumping and/or landing (49, 81). These findings could align decades across several Nordic countries. In Denmark, the incidence with the concept of the biomechanical chain and the broader chain rose from 26.9 per 100,000 person-years in 1994 to 31.7 in 2013 (66), theory of body linkage, in which impairments at the foot or ankle level while in Sweden it increased from 34.3 in 2017 to 41.7 in 2021 (67). may influence more proximal segments in order to maintain global Similarly, in Finland a rise from 17.3 to 32.3 per 100,000 person-years locomotor function. 34 INTRODUCTION KARI HUSETH 35 Human gait is not solely governed by mechanical or neuromuscular systems; psychological factors such as fear of reinjury, confidence, and emotional state can significantly influence gait and motor control, particularly during recovery after an injury (83). These psychological influences can play a critical role in post-injury adaptation. For example, fear of reinjury is prevalent among individuals one year after ATR, with over 50% of injured patients reporting such fear; an experience that correlates with lower Achilles Tendon Total Rupture Scores (ATRS) and observable alterations in movement strategies (84). This notion is echoed by Jónsdóttir et al., (85), who demonstrated shifts in joint power distribution during drop jumps in individuals with high fear of reinjury, despite no overt mechanical deficits. Such findings emphasize that movement alterations post-ATR are not only mechanical but may also reflect a biopsychosocial interplay between structural remodeling, neuromuscular control, and psychological readiness (86, 87). While psychological factors are undoubtedly important in shaping movement and recovery, this thesis is specifically focused on biomechanical and neuromuscular aspects, leaving psychological influences as a valuable area for future research. Given the Achilles tendon’s central role in propulsion and load FIGURE 9. Acute Achilles tendon rupture is typically described as a sudden blow or kick to the transmission during gait, its dysfunction provides a relevant context for back of the calf, accompanied by sharp pain and sometimes a distinct snapping sound. Following the injury, walking and running are severely impaired in most cases. exploring how local impairments may influence movement co-ordination throughout the kinetic chain. Emerging evidence suggests that the post-injury adaptations extend Although often implicitly assumed in clinical reasoning and theoretical beyond push-off mechanics and also aff ect early stance control (82). models, the idea that body segments interact as a part of a coordinated Normally, the deceleration of the body’s COM at initial contact is biomechanical chain has received limited direct investigations in the modulated by coordinated dorsifl exor, quadriceps, and hip extensor context of human locomotion. It is plausible that alterations in foot activity. Tibialis anterior controls ankle plantarfl exion in an eccentric kinematics-given the foot’s role as the initial point of contact with the mode, while the quadriceps and gluteus absorb impact and stabilize the ground-may influence neuromuscular activation and movement co- trunk. Post-ATR, however, altered activation pattern-including reduced ordination in more proximal segments, such as the hip and trunk. This is support moment at initial contact, have been observed, suggesting particularly relevant in conditions such as ATR, where local impairments impaired management of forward momentum (49, 79). may disrupt the timing and force generation during push-off, potentially 36 INTRODUCTION KARI HUSETH 37 Human gait is not solely governed by mechanical or neuromuscular systems; psychological factors such as fear of reinjury, confidence, and emotional state can significantly influence gait and motor control, particularly during recovery after an injury (83). These psychological influences can play a critical role in post-injury adaptation. For example, fear of reinjury is prevalent among individuals one year after ATR, with over 50% of injured patients reporting such fear; an experience that correlates with lower Achilles Tendon Total Rupture Scores (ATRS) and observable alterations in movement strategies (84). This notion is echoed by Jónsdóttir et al., (85), who demonstrated shifts in joint power distribution during drop jumps in individuals with high fear of reinjury, despite no overt mechanical deficits. Such findings emphasize that movement alterations post-ATR are not only mechanical but may also reflect a biopsychosocial interplay between structural remodeling, neuromuscular control, and psychological readiness (86, 87). While psychological factors are undoubtedly important in shaping movement and recovery, this thesis is specifically focused on biomechanical and neuromuscular aspects, leaving psychological influences as a valuable area for future research. Given the Achilles tendon’s central role in propulsion and load FIGURE 9. Acute Achilles tendon rupture is typically described as a sudden blow or kick to the transmission during gait, its dysfunction provides a relevant context for back of the calf, accompanied by sharp pain and sometimes a distinct snapping sound. Following the injury, walking and running are severely impaired in most cases. exploring how local impairments may influence movement co-ordination throughout the kinetic chain. Emerging evidence suggests that the post-injury adaptations extend Although often implicitly assumed in clinical reasoning and theoretical beyond push-off mechanics and also aff ect early stance control (82). models, the idea that body segments interact as a part of a coordinated Normally, the deceleration of the body’s COM at initial contact is biomechanical chain has received limited direct investigations in the modulated by coordinated dorsifl exor, quadriceps, and hip extensor context of human locomotion. It is plausible that alterations in foot activity. Tibialis anterior controls ankle plantarfl exion in an eccentric kinematics-given the foot’s role as the initial point of contact with the mode, while the quadriceps and gluteus absorb impact and stabilize the ground-may influence neuromuscular activation and movement co- trunk. Post-ATR, however, altered activation pattern-including reduced ordination in more proximal segments, such as the hip and trunk. This is support moment at initial contact, have been observed, suggesting particularly relevant in conditions such as ATR, where local impairments impaired management of forward momentum (49, 79). may disrupt the timing and force generation during push-off, potentially 36 INTRODUCTION KARI HUSETH 37 leading to compensatory strategies all along the lower limb and trunk. Such adaptations may be reflected in altered motor variability, which could serve as a mechanism to preserve functional performance and maintain postural control under changing mechanical demands such as those arising from varying physical activities, surface conditions, or movement intensities. The present thesis was driven by an interest to examine how local changes (nonpathological and pathological) at the foot and ankle- particularly involving the Achilles tendon-influence coordination along the kinematic chain during walking and running. Despite its central role in propulsion, the broader impact of Achilles tendon dysfunction on whole-body movement remains poorly understood, in part due to the complexity of studying multi-segment interactions. Through these studies, the overarching aim was to address these gaps and contribute to a better understanding of locomotor adaptation and recovery. 38 INTRODUCTION KARI HUSETH 39 leading to compensatory strategies all along the lower limb and trunk. Such adaptations may be reflected in altered motor variability, which could serve as a mechanism to preserve functional performance and maintain postural control under changing mechanical demands such as those arising from varying physical activities, surface conditions, or movement intensities. The present thesis was driven by an interest to examine how local changes (nonpathological and pathological) at the foot and ankle- particularly involving the Achilles tendon-influence coordination along the kinematic chain during walking and running. Despite its central role in propulsion, the broader impact of Achilles tendon dysfunction on whole-body movement remains poorly understood, in part due to the complexity of studying multi-segment interactions. Through these studies, the overarching aim was to address these gaps and contribute to a better understanding of locomotor adaptation and recovery. 38 INTRODUCTION KARI HUSETH 39 2. Knowledge gaps There is limited evidence comparing EMG normalization strategies across postural conditions, and it remains unclear how the test positions supine versus standing affect MVIC values for lower extremities and trunk muscles. The influence of foot posture, i.e. neutral, pronated, or supinated in lower extremity and trunk muscle activation during functional tasks has not been clearly established, limiting the understanding of how distal alignment affects segmental coordination. There is insufficient knowledge of how an ATR affects lower-limb joint mechanics and muscle activation patterns during the stance phase of walking and jogging, particularly with regard to persistent between-the- limbs asymmetries after tendon rupture. The distribution of neuromechanical adaptations along the kinematic chain from the ankle to the trunk following an ATR remains poorly understood, especially in terms of how altered distal function influences proximal joint coordination and supports strategies during walking and running. Løpe fra meg selv? – Nei, det går ikke an. Run away from myself? – No, that cannot be done. 👥👥 PER GYNT, HENRIK IBSEN 40 KNOWLEGDE GAP KARI HUSETH 41 2. Knowledge gaps There is limited evidence comparing EMG normalization strategies across postural conditions, and it remains unclear how the test positions supine versus standing affect MVIC values for lower extremities and trunk muscles. The influence of foot posture, i.e. neutral, pronated, or supinated in lower extremity and trunk muscle activation during functional tasks has not been clearly established, limiting the understanding of how distal alignment affects segmental coordination. There is insufficient knowledge of how an ATR affects lower-limb joint mechanics and muscle activation patterns during the stance phase of walking and jogging, particularly with regard to persistent between-the- limbs asymmetries after tendon rupture. The distribution of neuromechanical adaptations along the kinematic chain from the ankle to the trunk following an ATR remains poorly understood, especially in terms of how altered distal function influences proximal joint coordination and supports strategies during walking and running. Løpe fra meg selv? – Nei, det går ikke an. Run away from myself? – No, that cannot be done. 👥👥 PER GYNT, HENRIK IBSEN 40 KNOWLEGDE GAP KARI HUSETH 41 3. Aims The overall goal of this thesis is to advance the understanding of the biomechanical chain mechanism from the feet up to the trunk. This includes investigating how foot kinematics influence muscle activation in the lower extremities, pelvis, and trunk, alongside kinematic and kinetic measurements of interconnected body segments during various functional activities. Methodological investigations address how the position used for MVIC, standing versus supine, affects EMG normalization, thereby influencing the interpretation of muscle activation patterns in relation to foot kinematics. STUDY I To compare the MVIC EMG normalization method for selected lower extremity and trunk muscles when using standardized supine versus standing test positions. STUDY II To compare the activation of selected trunk, pelvic and lower extremity muscles during neutral, pronated, and supinated stance conditions during a standardized vertical step maneuver. STUDY III To investigate the limb-to-limb differences in kinematics, kinetics, and muscle activation patterns of the lower extremities during the stance phase of walking and jogging, one year after an ATR. STUDY IV To investigate side-to-side differences in muscle activation, range of Two roads diverged in the woods, and I–. motion, joint power, joint moment and support moment during walking I took the one less travel by, and running one year after an acute ATR with specific emphasis on And that has made all the difference. segmental adaptations within the ankle–knee–hip complex and their 👥👥 ROBERT FROST distribution along the kinematic chain up to the trunk. 42 AIMS KARI HUSETH 43 3. Aims The overall goal of this thesis is to advance the understanding of the biomechanical chain mechanism from the feet up to the trunk. This includes investigating how foot kinematics influence muscle activation in the lower extremities, pelvis, and trunk, alongside kinematic and kinetic measurements of interconnected body segments during various functional activities. Methodological investigations address how the position used for MVIC, standing versus supine, affects EMG normalization, thereby influencing the interpretation of muscle activation patterns in relation to foot kinematics. STUDY I To compare the MVIC EMG normalization method for selected lower extremity and trunk muscles when using standardized supine versus standing test positions. STUDY II To compare the activation of selected trunk, pelvic and lower extremity muscles during neutral, pronated, and supinated stance conditions during a standardized vertical step maneuver. STUDY III To investigate the limb-to-limb differences in kinematics, kinetics, and muscle activation patterns of the lower extremities during the stance phase of walking and jogging, one year after an ATR. STUDY IV To investigate side-to-side differences in muscle activation, range of Two roads diverged in the woods, and I–. motion, joint power, joint moment and support moment during walking I took the one less travel by, and running one year after an acute ATR with specific emphasis on And that has made all the difference. segmental adaptations within the ankle–knee–hip complex and their 👥👥 ROBERT FROST distribution along the kinematic chain up to the trunk. 42 AIMS KARI HUSETH 43 4. Ethical approvals All studies were approved by either the  Regional Ethical Review Board in Gothenburg (Studies I and II) or the  Swedish Ethical Review Authority (Studies III and IV), (Table 2). All procedures were conducted in accordance with the ethical principles outlined in the Declaration of Helsinki. TABLE 2. Ethical approvals of Studies I-IV. Studies Ethical board Date of D-nr approval I, II Regional ethical review board, Gothenburg 14-09-25 514-14 III Swedish ethical review authority 19-11-20 2019-05457 IV 22-03-18 2022-00921-02 Umveg er jamt, til utrygg ven, Um midt i bygdi han bur. Men beinvegar gjeng till den gode venen, Um han er langt av leid. The road is long to a false friend, Even if he lives next door. But the way is short to a true friend, Though he may live far more. 👥👥 HÅVAMÅL (DEN ELDRE EDDA) 44 ETHICAL APPROVALS KARI HUSETH 45 4. Ethical approvals All studies were approved by either the  Regional Ethical Review Board in Gothenburg (Studies I and II) or the  Swedish Ethical Review Authority (Studies III and IV), (Table 2). All procedures were conducted in accordance with the ethical principles outlined in the Declaration of Helsinki. TABLE 2. Ethical approvals of Studies I-IV. Studies Ethical board Date of D-nr approval I, II Regional ethical review board, Gothenburg 14-09-25 514-14 III Swedish ethical review authority 19-11-20 2019-05457 IV 22-03-18 2022-00921-02 Umveg er jamt, til utrygg ven, Um midt i bygdi han bur. Men beinvegar gjeng till den gode venen, Um han er langt av leid. The road is long to a false friend, Even if he lives next door. But the way is short to a true friend, Though he may live far more. 👥👥 HÅVAMÅL (DEN ELDRE EDDA) 44 ETHICAL APPROVALS KARI HUSETH 45 5. Introduction to This thesis employed three primary biomechanical assessment biomechanical tools modalities: EMG, kinematics, and kinetics. All measurements were performed at the Gait Laboratory of the Orthopedic Research Unit, Sahlgrenska Academy, University of Gothenburg. ELECTROMYOGRAPHY (EMG) Electromyography (EMG) was used to evaluate neuromuscular activity during movement. EMG evaluates muscle function by recording the electrical signals generated within muscle fibers in response to neural stimulation. This technique provides insights into motor unit activation patterns, timing, and coordination. Recording of EMG can either be conducted intramuscularly, using needle electrodes, or using surface electrodes (sEMG) applied directly to the skin (10, 88). The latter approach is most frequently used in biomechanical investigations (89, 90). These recordings capture the electrical activation produced by muscle contractions, which originate at the level of the motor unit. A motor unit consists of a single motor neuron and the muscle fibers it innervates. When a motor neuron sends an action potential, it triggers an electrical response in the muscle, known as a motor unit action potential (MUAP). This process initiates muscle contraction, which is the basis of EMG recordings (28), (Figure 10). SURFACE EMG (sEMG) Surface EMG is a non-invasive method for recording electrical activity from muscles using electrodes placed on the skin. Before applying the bipolar sets of electrodes, proper skin preparation is essential to ensure accurate signal acquisition. This typically involves shaving hair at the area with a razor and cleaning the skin with an alcohol rub to remove debris (91), (Figure 11). Not all those who wander are lost. 👥👥 J.R.R. TOLKIEN 46 I NTRODUCTION TO BIOMECHANICAL TOOLS KARI HUSETH 47 5. Introduction to This thesis employed three primary biomechanical assessment biomechanical tools modalities: EMG, kinematics, and kinetics. All measurements were performed at the Gait Laboratory of the Orthopedic Research Unit, Sahlgrenska Academy, University of Gothenburg. ELECTROMYOGRAPHY (EMG) Electromyography (EMG) was used to evaluate neuromuscular activity during movement. EMG evaluates muscle function by recording the electrical signals generated within muscle fibers in response to neural stimulation. This technique provides insights into motor unit activation patterns, timing, and coordination. Recording of EMG can either be conducted intramuscularly, using needle electrodes, or using surface electrodes (sEMG) applied directly to the skin (10, 88). The latter approach is most frequently used in biomechanical investigations (89, 90). These recordings capture the electrical activation produced by muscle contractions, which originate at the level of the motor unit. A motor unit consists of a single motor neuron and the muscle fibers it innervates. When a motor neuron sends an action potential, it triggers an electrical response in the muscle, known as a motor unit action potential (MUAP). This process initiates muscle contraction, which is the basis of EMG recordings (28), (Figure 10). SURFACE EMG (sEMG) Surface EMG is a non-invasive method for recording electrical activity from muscles using electrodes placed on the skin. Before applying the bipolar sets of electrodes, proper skin preparation is essential to ensure accurate signal acquisition. This typically involves shaving hair at the area with a razor and cleaning the skin with an alcohol rub to remove debris (91), (Figure 11). Not all those who wander are lost. 👥👥 J.R.R. TOLKIEN 46 I NTRODUCTION TO BIOMECHANICAL TOOLS KARI HUSETH 47 Electrode application follows a standardized muscle map to ensure accurate placement over the target muscle (92-94). The procedure sampling process includes: • Recording in rest to capture baseline muscle activity • Signal check to ensure the quality and integrity of data • Crosstalk check to detect interference from adjacent muscles • Maximum voluntary isometric contraction (MVIC) recording as per established protocol • Target muscle action recording during specific tasks, also according to a specific protocol These procedures may need to be repeated to ensure the highest available data reliability and consistency. sEMG SIGNAL PROCESSING EMG signals can be affected by various sources of noise, including motion artifacts from electrode or cable movement, poor skin-electrode FIGURE 10. Schematic representation of the pathway from neural activation to raw surface EMG signal. The process begins with motor commands in the ventral horn of the spinal cord, contact, electrical interference from surrounding equipment or lighting, traveling via the ventral root and alpha motor neuron axon to the neuromuscular junction. This and cross-talk from nearby muscles. triggers motor unit action potentials (MUAPs), which sum across multiple motor units to produce a complex signal in the muscle tissue. Surface electromyography (bipolar sEMG) detects this Signal processing of sEMG involves both analog and digital stages summed activity at the skin surface, producing a raw EMG signal that contains motor unit action (95-97) potentials (MUAPs), along with noise and artifacts. . Signal processing is essential to maximize the capture and representation of muscle activation within the sampled data. Analog processing occurs at the electrode-skin interface and includes capturing the raw sEMG signal, signal amplification and applying an analog bandpass filter to reduce electrical and mechanical (movement) noise and enhance signal quality. Digital processing is performed using highly specialized software. This typically involves a digital linear FIGURE 11. Skin preparation: Hair is fi rst removed with a razor, after envelope, which includes high-pass filter to remove low-frequency which the area is cleaned with an noise (movement artifacts), rectification to convert all signal values to alcohol swab to eliminate skin positive, a low-pass filter, often implemented as a root mean square debris and oils, ensuring optimal electrode–skin contact. (RMS) moving window, to smoothen the signal (Figure 12). 48 INTRODUCTION TO BIOMECHANICAL TOOLS KARI HUSETH 49 Electrode application follows a standardized muscle map to ensure accurate placement over the target muscle (92-94). The procedure sampling process includes: • Recording in rest to capture baseline muscle activity • Signal check to ensure the quality and integrity of data • Crosstalk check to detect interference from adjacent muscles • Maximum voluntary isometric contraction (MVIC) recording as per established protocol • Target muscle action recording during specific tasks, also according to a specific protocol These procedures may need to be repeated to ensure the highest available data reliability and consistency. sEMG SIGNAL PROCESSING EMG signals can be affected by various sources of noise, including motion artifacts from electrode or cable movement, poor skin-electrode FIGURE 10. Schematic representation of the pathway from neural activation to raw surface EMG signal. The process begins with motor commands in the ventral horn of the spinal cord, contact, electrical interference from surrounding equipment or lighting, traveling via the ventral root and alpha motor neuron axon to the neuromuscular junction. This and cross-talk from nearby muscles. triggers motor unit action potentials (MUAPs), which sum across multiple motor units to produce a complex signal in the muscle tissue. Surface electromyography (bipolar sEMG) detects this Signal processing of sEMG involves both analog and digital stages summed activity at the skin surface, producing a raw EMG signal that contains motor unit action (95-97) potentials (MUAPs), along with noise and artifacts. . Signal processing is essential to maximize the capture and representation of muscle activation within the sampled data. Analog processing occurs at the electrode-skin interface and includes capturing the raw sEMG signal, signal amplification and applying an analog bandpass filter to reduce electrical and mechanical (movement) noise and enhance signal quality. Digital processing is performed using highly specialized software. This typically involves a digital linear FIGURE 11. Skin preparation: Hair is fi rst removed with a razor, after envelope, which includes high-pass filter to remove low-frequency which the area is cleaned with an noise (movement artifacts), rectification to convert all signal values to alcohol swab to eliminate skin positive, a low-pass filter, often implemented as a root mean square debris and oils, ensuring optimal electrode–skin contact. (RMS) moving window, to smoothen the signal (Figure 12). 48 INTRODUCTION TO BIOMECHANICAL TOOLS KARI HUSETH 49 MOTION CAPTURE SYSTEM (MOCAP) A A three-dimensional optical camera system that uses reflective markers attached to well-defined anatomical landmarks, motion capture system (MOCAP) given body movements (kinematic action) can be recorded and analyzed (Figure 13). The markers are applied to the skin according to the given marker model, which refers to a specific algorithm (99), B (Figure 14). 1 The MOCAP is synchronized with a force plate system that registers the external forces (kinetic actions) affecting the musculoskeletal system during the survey. This is done by performing weight-bearing movements on instrumented force plates either in the form of walking, 2 jogging, jumping or hopping. 3 FIGURE 12. A: The analog raw EMG signal detection during the stance phase of lateral gastrocnemius muscle (one single trial) during stance phase of gait. B: the digital filtering process from 1) high pass filter 2) the detrending process to 3) the RMS process to the final signal output. NORMALIZATION To ensure meaningful comparisons across individuals or conditions, normalization of EMG signals is critical. This can be applied in different FIGURE 13. From the gait lab, the motion capture system with cameras and force plates. A ways, but most used is amplitude normalization to a reference value, participant is equipped with surface EMG sensors and reflective markers and is walking on the such as the peak EMG signal measured during a MVIC (98). Task-specific 10-meter stationary walkway, which is equipped with the timing system. normalization based on activity relevant to the muscle function being studied is another way of performing a signal normalization. 50 I NTRODUCTION TO BIOMECHANICAL TOOLS KARI HUSETH 51 MOTION CAPTURE SYSTEM (MOCAP) A A three-dimensional optical camera system that uses reflective markers attached to well-defined anatomical landmarks, motion capture system (MOCAP) given body movements (kinematic action) can be recorded and analyzed (Figure 13). The markers are applied to the skin according to the given marker model, which refers to a specific algorithm (99), B (Figure 14). 1 The MOCAP is synchronized with a force plate system that registers the external forces (kinetic actions) affecting the musculoskeletal system during the survey. This is done by performing weight-bearing movements on instrumented force plates either in the form of walking, 2 jogging, jumping or hopping. 3 FIGURE 12. A: The analog raw EMG signal detection during the stance phase of lateral gastrocnemius muscle (one single trial) during stance phase of gait. B: the digital filtering process from 1) high pass filter 2) the detrending process to 3) the RMS process to the final signal output. NORMALIZATION To ensure meaningful comparisons across individuals or conditions, normalization of EMG signals is critical. This can be applied in different FIGURE 13. From the gait lab, the motion capture system with cameras and force plates. A ways, but most used is amplitude normalization to a reference value, participant is equipped with surface EMG sensors and reflective markers and is walking on the such as the peak EMG signal measured during a MVIC (98). Task-specific 10-meter stationary walkway, which is equipped with the timing system. normalization based on activity relevant to the muscle function being studied is another way of performing a signal normalization. 50 I NTRODUCTION TO BIOMECHANICAL TOOLS KARI HUSETH 51 A B C FIGURE 14. The biomechanical six degree of freedom (6-DOF) model with refl ective markers on anatomical landmarks and skeletal reconstruction shown in (A) frontal, (B) dorsal, and (C) lateral views. The laboratory coordinate system (X: red, Y: green, Z: blue) defi nes the global reference system. Force plates embedded in the walkway capture ground reaction forces, which together with kinematic data from the marker model are used to calculate joint moment and power across the kinetic chain by inverse dynamics. The vertical and horizontal forces exerted by the foot onto the force plate allow for quantifi cation of the opposing ground reaction forces. FIGURE 15. Cartesian coordinate system with the three axes (x, y, z). The sagittal plane is defi ned At the same time, joint angles and body segment positions are recorded by the x–z axes (i.e., fl exion and extension), the frontal plane by the y–z axes (i.e., abduction and adduction), and the transverse plane by the x–y axes (i.e., rotation). This system provides the by the MOCAP, which tracks refl ective markers in the global Cartesian spatial reference for describing human movement. coordinate system (x, y, z). These axes correspond to the anatomical planes of motion: sagittal (forward-backward), frontal (side-to-side), and transverse (rotational), (Figure 15). This combined approach-integrating kinematic data from motion capture and external force data from force plates-enables the calculation of joint kinetics through inverse dynamics calculations (1). Kinematics refers to the study of movement without consideration of the forces that produce the motion. In the present project, segmental movement was captured using the MOCAP, which relies on high-speed cameras to track refl ective markers placed on anatomical landmarks. This set-up enables precise measurement of joint angles, segment orientation, and whole-body motion yielding a detailed representation of movement patterns. 52 INTRODUCTION TO BIOMECHANICAL TOOLS KARI HUSETH 53 A B C FIGURE 14. The biomechanical six degree of freedom (6-DOF) model with refl ective markers on anatomical landmarks and skeletal reconstruction shown in (A) frontal, (B) dorsal, and (C) lateral views. The laboratory coordinate system (X: red, Y: green, Z: blue) defi nes the global reference system. Force plates embedded in the walkway capture ground reaction forces, which together with kinematic data from the marker model are used to calculate joint moment and power across the kinetic chain by inverse dynamics. The vertical and horizontal forces exerted by the foot onto the force plate allow for quantifi cation of the opposing ground reaction forces. FIGURE 15. Cartesian coordinate system with the three axes (x, y, z). The sagittal plane is defi ned At the same time, joint angles and body segment positions are recorded by the x–z axes (i.e., fl exion and extension), the frontal plane by the y–z axes (i.e., abduction and adduction), and the transverse plane by the x–y axes (i.e., rotation). This system provides the by the MOCAP, which tracks refl ective markers in the global Cartesian spatial reference for describing human movement. coordinate system (x, y, z). These axes correspond to the anatomical planes of motion: sagittal (forward-backward), frontal (side-to-side), and transverse (rotational), (Figure 15). This combined approach-integrating kinematic data from motion capture and external force data from force plates-enables the calculation of joint kinetics through inverse dynamics calculations (1). Kinematics refers to the study of movement without consideration of the forces that produce the motion. In the present project, segmental movement was captured using the MOCAP, which relies on high-speed cameras to track refl ective markers placed on anatomical landmarks. This set-up enables precise measurement of joint angles, segment orientation, and whole-body motion yielding a detailed representation of movement patterns. 52 INTRODUCTION TO BIOMECHANICAL TOOLS KARI HUSETH 53 Kinetics, in contrast, focuses on the forces underlying motion. Central Newton’s 2nd (Figure 17) and 3rd (Figure 16) laws to work backward from to the kinetic analysis is Newton´s 3rd law (Figure 16), which states movement to determine the net mechanical demands placed on each that for every action, there is an equal and opposite reaction. Ground joint. This approach is essential for understanding joint loading during reaction forces (GRFs), measured via force plates, play a critical role in walking and running. this analysis. When combined with kinematic data and known segmental properties (e.g., mass and inertia), GRFs allow for the calculation of internal joint forces and moments through inverse dynamics. FIGURE 17. Newton’s 2nd Law of Motion. A force (F) applied to a crate of mass (m) produces an acceleration (a) in the direction of the applied force, consistent with the relationship  F = ma. According to Newton’s 2nd law, the net force acting on an object is equal to the product of its mass FIGURE 16. Newton’s 3rd law. (a) The runner exerts a force downward and backward onto the and acceleration. In inverse dynamics, this principle provides the foundation for calculating net ground. (b) In response, the ground applies an equal and opposite reaction force upward and joint forces and moments: the linear acceleration of each segment’s center of mass is related forward, propelling the runner forward. to the net force acting on it, while the angular acceleration is related to the net moment. By combining measured ground reaction forces with segmental kinematics, these equations yield the internal net joint moments that refl ect the combined action of muscles and passive structures across the joints. Inverse dynamics represents a computational method used to estimate internal joint forces and moments based on measured motion patterns ( joint angles) and external forces. By combining kinematic data These integrated biomechanical measures-muscle activation, (e.g., joint angles and segment accelerations) with GRFs and known movement patterns, and force generation-form the foundation of the segmental properties (mass and inertia), inverse dynamics applies analyses performed in this thesis (Table 3). 54 INTRODUCTION TO BIOMECHANICAL TOOLS KARI HUSETH 55 Kinetics, in contrast, focuses on the forces underlying motion. Central Newton’s 2nd (Figure 17) and 3rd (Figure 16) laws to work backward from to the kinetic analysis is Newton´s 3rd law (Figure 16), which states movement to determine the net mechanical demands placed on each that for every action, there is an equal and opposite reaction. Ground joint. This approach is essential for understanding joint loading during reaction forces (GRFs), measured via force plates, play a critical role in walking and running. this analysis. When combined with kinematic data and known segmental properties (e.g., mass and inertia), GRFs allow for the calculation of internal joint forces and moments through inverse dynamics. FIGURE 17. Newton’s 2nd Law of Motion. A force (F) applied to a crate of mass (m) produces an acceleration (a) in the direction of the applied force, consistent with the relationship  F = ma. According to Newton’s 2nd law, the net force acting on an object is equal to the product of its mass FIGURE 16. Newton’s 3rd law. (a) The runner exerts a force downward and backward onto the and acceleration. In inverse dynamics, this principle provides the foundation for calculating net ground. (b) In response, the ground applies an equal and opposite reaction force upward and joint forces and moments: the linear acceleration of each segment’s center of mass is related forward, propelling the runner forward. to the net force acting on it, while the angular acceleration is related to the net moment. By combining measured ground reaction forces with segmental kinematics, these equations yield the internal net joint moments that refl ect the combined action of muscles and passive structures across the joints. Inverse dynamics represents a computational method used to estimate internal joint forces and moments based on measured motion patterns ( joint angles) and external forces. By combining kinematic data These integrated biomechanical measures-muscle activation, (e.g., joint angles and segment accelerations) with GRFs and known movement patterns, and force generation-form the foundation of the segmental properties (mass and inertia), inverse dynamics applies analyses performed in this thesis (Table 3). 54 INTRODUCTION TO BIOMECHANICAL TOOLS KARI HUSETH 55 6. Data collection; Studies I-IV METHODS The studies in this thesis are divided into two main categories: Studies I–II focused on methodological development, including EMG normalization and foot position during movement tasks. Studies III–IV explored the biomechanical consequences of an ATR on walking and running, with particular attention to how such injuries affect the biomechanical chain from the foot to the trunk. TABLE 3: Biomechanical tools and variables. Study I Study II Study III Study IV ELECTROMYOGRAPHY MVIC -supine vs standing ✔ %MVIC-mean amplitude foot kinematic ✔ EMG%-during stance periods IC-MS, MS-TO ✔ ✔ MOCAP ROM for stance periods: IC-MS, MS-TO ✔ Joint positions at IC, MS, TO ✔ ROM for IC-TO ✔ Joint moment mean during periods: IC-TO (Nm/kg) ✔ Joint moment at IC, MS, TO (Nm/kg) ✔ Joint power during IC-TO (watt/kg) ✔ PHYSICAL ASSESSMENT TOOL Navicular drop test ✔ PROMs EQ-5D ✔ ✔ PAS ✔ ✔ MVIC = maximum voluntary isometric contraction, %MVIC = EMG amplitude normalized to maximum voluntary isometric contraction (100%), EMG % = detrended EMG expressed relative to %MVIC, IC = initial contact, MS = midstance, TO = toe-off, IC-MS = initial contact to midstance, MS-TO = midstance to toe-off, ROM = range of That’s the thing about running: your greatest runs are rarely motion, PROMs = patient reported outcome measures, EQ-5D = EuroQol 5 Dimensions, PAS = physical activity scale measured by racing success. They are moments in time when running allows you to see how wonderful your life is. 👥👥 KARA GOUCHER 56 DATA COLLECTION; STUDIES I-IV KARI HUSETH 57 6. Data collection; Studies I-IV METHODS The studies in this thesis are divided into two main categories: Studies I–II focused on methodological development, including EMG normalization and foot position during movement tasks. Studies III–IV explored the biomechanical consequences of an ATR on walking and running, with particular attention to how such injuries affect the biomechanical chain from the foot to the trunk. TABLE 3: Biomechanical tools and variables. Study I Study II Study III Study IV ELECTROMYOGRAPHY MVIC -supine vs standing ✔ %MVIC-mean amplitude foot kinematic ✔ EMG%-during stance periods IC-MS, MS-TO ✔ ✔ MOCAP ROM for stance periods: IC-MS, MS-TO ✔ Joint positions at IC, MS, TO ✔ ROM for IC-TO ✔ Joint moment mean during periods: IC-TO (Nm/kg) ✔ Joint moment at IC, MS, TO (Nm/kg) ✔ Joint power during IC-TO (watt/kg) ✔ PHYSICAL ASSESSMENT TOOL Navicular drop test ✔ PROMs EQ-5D ✔ ✔ PAS ✔ ✔ MVIC = maximum voluntary isometric contraction, %MVIC = EMG amplitude normalized to maximum voluntary isometric contraction (100%), EMG % = detrended EMG expressed relative to %MVIC, IC = initial contact, MS = midstance, TO = toe-off, IC-MS = initial contact to midstance, MS-TO = midstance to toe-off, ROM = range of That’s the thing about running: your greatest runs are rarely motion, PROMs = patient reported outcome measures, EQ-5D = EuroQol 5 Dimensions, PAS = physical activity scale measured by racing success. They are moments in time when running allows you to see how wonderful your life is. 👥👥 KARA GOUCHER 56 DATA COLLECTION; STUDIES I-IV KARI HUSETH 57 TABLE 4. Description of electrode placements for the EMG sampling performed in Studies I-IV. TABLE 5. EMG recorded in Studies I–IV. Muscle Electrode placement description Studies EMG target muscles Study I Study II Study III Study IV Tibialis anterior Lateral to the medial shaft of tibia, approximately 1/3 of the I, II, III, IV Tibialis anterior ✔ ✔ ✔ ✔ distance between knee and ankle, over the largest muscle mass, in slightly oblique direction Peroneus longus ✔ Peroneus longus A line is drawn between the head of the fibula and the lateral II malleolus, medial to muscle belly of the Medial gastrocnemius ✔ ✔ tibialis anterior muscle Lateral gastrocnemius ✔ ✔ Soleus medialis Just under the belly of gastrocnemius, a line is drawn II, III, IV between the medial side of the Achilles tendon insertion and Medial soleus ✔ ✔ ✔ the head of the fibula Vastus medialis ✔ Medial gastocnemius Parallel to muscle fibers, just distally to the knee, 2 cm III, IV medially to the midline of the dorsal aspect of the shank Gluteus medius ✔ ✔ ✔ Lateral gastrocnemius Parallel to muscle fibers, just distal to knee and 2 cm laterally III, IV to midline of the dorsal aspect of the shank Adductor longus ✔ ✔ Vastus lateralis Appoximately 2 cm medial from superior rim of patella, in an IV Rectus abdominis ✔ ✔ oblique direction (ca 55 degrees) External oblique ✔ ✔ ✔ Adductor longus Medial aspect of thigh, approximately 4 cm from the pubic I, II bones, in an oblique direction Internal oblique/Transversus abdominis ✔ ✔ Gluteus medius Approximately 1/3 of the distance between the iliac crest and I, II, IV Erector spinae (lumbar) ✔ ✔ greater trochanter, anterior to gluteus maximus muscle Multifidus (lumbar) ✔ Rectus abdominus Approximately 3 cm superior to umbilicus and 2 cm lateral to I, II, IV midline External oblique Direct in a lateral line from umbilicus. Approximately 12-15 I, II, IV STUDIES I-II cm, directly above the anterior superior iliac spine, halfway between the pelvic crest and the ribs, in a slightly oblique In Studies I and II, EMG data were collected using a Noraxon Telemyo angle desktop (16 channels) and a Noraxon Telemyo belt system (8-channel) Internal oblique/ Approximately 2 cm medial and inferior to anterior superior I, II Scottsdale, USA, wireless receivers EMG system using a bandwidth Transversus iliac spine (SIPS), on a line midway between SIPS and pubis, abdominis just superior to the inguinal ligament filter of 10-500 Hz. Pre-amplification of all signals was performed with a baseline noise of <1μV RMS, input impedance of >100 MW and a Erector spinae Laterally to the spinal process of L3, approximately 2 cm from II, IV (lumbar) the spine common mode rejection ratio of >100 dB. Data sampling frequency was 1500 Hz using a 16-bit external A/D converter. Multifidus (lumbar) Laterally to L5 spinal process, medially to spina iliaca II posterior superior (SIPS) In both studies, surface electrodes (AMBU Blue Sensor N, Copenhagen, Denmark) were applied, and post-hoc processing of EMG signals was conducted using Noraxon MR3 software (version 3.8, Scottsdale, USA). 58 DATA COLLECTION; STUDIES I-IV KARI HUSETH 59 TABLE 4. Description of electrode placements for the EMG sampling performed in Studies I-IV. TABLE 5. EMG recorded in Studies I–IV. Muscle Electrode placement description Studies EMG target muscles Study I Study II Study III Study IV Tibialis anterior Lateral to the medial shaft of tibia, approximately 1/3 of the I, II, III, IV Tibialis anterior ✔ ✔ ✔ ✔ distance between knee and ankle, over the largest muscle mass, in slightly oblique direction Peroneus longus ✔ Peroneus longus A line is drawn between the head of the fibula and the lateral II malleolus, medial to muscle belly of the Medial gastrocnemius ✔ ✔ tibialis anterior muscle Lateral gastrocnemius ✔ ✔ Soleus medialis Just under the belly of gastrocnemius, a line is drawn II, III, IV between the medial side of the Achilles tendon insertion and Medial soleus ✔ ✔ ✔ the head of the fibula Vastus medialis ✔ Medial gastocnemius Parallel to muscle fibers, just distally to the knee, 2 cm III, IV medially to the midline of the dorsal aspect of the shank Gluteus medius ✔ ✔ ✔ Lateral gastrocnemius Parallel to muscle fibers, just distal to knee and 2 cm laterally III, IV to midline of the dorsal aspect of the shank Adductor longus ✔ ✔ Vastus lateralis Appoximately 2 cm medial from superior rim of patella, in an IV Rectus abdominis ✔ ✔ oblique direction (ca 55 degrees) External oblique ✔ ✔ ✔ Adductor longus Medial aspect of thigh, approximately 4 cm from the pubic I, II bones, in an oblique direction Internal oblique/Transversus abdominis ✔ ✔ Gluteus medius Approximately 1/3 of the distance between the iliac crest and I, II, IV Erector spinae (lumbar) ✔ ✔ greater trochanter, anterior to gluteus maximus muscle Multifidus (lumbar) ✔ Rectus abdominus Approximately 3 cm superior to umbilicus and 2 cm lateral to I, II, IV midline External oblique Direct in a lateral line from umbilicus. Approximately 12-15 I, II, IV STUDIES I-II cm, directly above the anterior superior iliac spine, halfway between the pelvic crest and the ribs, in a slightly oblique In Studies I and II, EMG data were collected using a Noraxon Telemyo angle desktop (16 channels) and a Noraxon Telemyo belt system (8-channel) Internal oblique/ Approximately 2 cm medial and inferior to anterior superior I, II Scottsdale, USA, wireless receivers EMG system using a bandwidth Transversus iliac spine (SIPS), on a line midway between SIPS and pubis, abdominis just superior to the inguinal ligament filter of 10-500 Hz. Pre-amplification of all signals was performed with a baseline noise of <1μV RMS, input impedance of >100 MW and a Erector spinae Laterally to the spinal process of L3, approximately 2 cm from II, IV (lumbar) the spine common mode rejection ratio of >100 dB. Data sampling frequency was 1500 Hz using a 16-bit external A/D converter. Multifidus (lumbar) Laterally to L5 spinal process, medially to spina iliaca II posterior superior (SIPS) In both studies, surface electrodes (AMBU Blue Sensor N, Copenhagen, Denmark) were applied, and post-hoc processing of EMG signals was conducted using Noraxon MR3 software (version 3.8, Scottsdale, USA). 58 DATA COLLECTION; STUDIES I-IV KARI HUSETH 59 In Study I, two positions were compared for the performance of the MVIC Prior to electrode placement, the skin was prepared according to the EMG normalization method: supine and standing. For each target muscle, standard procedure to reduce impedance and improve signal quality (92). participants performed three consecutive MVICs, each lasting three seconds, with a three-second rest between repetitions. A one-minute The electrodes were connected via wires to Noraxon DTR sensors, rest period was provided between testing of different muscle groups which wirelessly transmitted EMG data to a central receiver unit. Before to minimize fatigue. Throughout the testing protocol, participants data acquisition, a thorough signal quality check was conducted to were guided with standardized verbal encouragement. External static confirm signal stability and rule out crosstalk from adjacent muscles. resistance was standardized and applied both manually by the examiner This was achieved through visual inspection of real-time EMG signals and with adjustable straps to ensure consistent resistance to the tested during light-to-moderate voluntary contractions of each target muscle. muscles (Figure 18). In Study II, muscle activation of selected trunk, pelvic, and lower extremity muscles was measured during neutral, pronated, and A B supinated stance conditions in a standardized vertical step maneuver (Tables, 4,5). The test zone was marked with tape lines corresponding to each participant’s individually determined neutral stance, ensuring a reproducible foot starting position before initiating the step ascent action (Figure 19). FIGURE 18. The two MVIC positions; (A) supine and (B) standing investigated in Study I. Surface electromyographic (sEMG) activity was recorded bilaterally from six target muscles: tibialis anterior (TA), gluteus medius (GlM), adductor longus (ADDl), rectus abdominis (RA), external oblique (OE), FIGURE 19. The test zone is marked with and the internal oblique/transversus abdominis (IO/TrA) complex (91, 93, tape lines for the foot positions studied in Study II. The tape lines corresponded to each 94), (Tables 4,5). Bipolar surface electrodes with a 20 mm inter-electrode participant’s individually determined neutral distance were placed with the participant in a standing position. stance, ensuring a reproducible foot starting Electrode placement followed established protocols as described in position before initiating the step ascent action. Table 4, (91, 93, 94). 60 DATA COLLECTION; STUDIES I-IV KARI HUSETH 61 In Study I, two positions were compared for the performance of the MVIC Prior to electrode placement, the skin was prepared according to the EMG normalization method: supine and standing. For each target muscle, standard procedure to reduce impedance and improve signal quality (92). participants performed three consecutive MVICs, each lasting three seconds, with a three-second rest between repetitions. A one-minute The electrodes were connected via wires to Noraxon DTR sensors, rest period was provided between testing of different muscle groups which wirelessly transmitted EMG data to a central receiver unit. Before to minimize fatigue. Throughout the testing protocol, participants data acquisition, a thorough signal quality check was conducted to were guided with standardized verbal encouragement. External static confirm signal stability and rule out crosstalk from adjacent muscles. resistance was standardized and applied both manually by the examiner This was achieved through visual inspection of real-time EMG signals and with adjustable straps to ensure consistent resistance to the tested during light-to-moderate voluntary contractions of each target muscle. muscles (Figure 18). In Study II, muscle activation of selected trunk, pelvic, and lower extremity muscles was measured during neutral, pronated, and A B supinated stance conditions in a standardized vertical step maneuver (Tables, 4,5). The test zone was marked with tape lines corresponding to each participant’s individually determined neutral stance, ensuring a reproducible foot starting position before initiating the step ascent action (Figure 19). FIGURE 18. The two MVIC positions; (A) supine and (B) standing investigated in Study I. Surface electromyographic (sEMG) activity was recorded bilaterally from six target muscles: tibialis anterior (TA), gluteus medius (GlM), adductor longus (ADDl), rectus abdominis (RA), external oblique (OE), FIGURE 19. The test zone is marked with and the internal oblique/transversus abdominis (IO/TrA) complex (91, 93, tape lines for the foot positions studied in Study II. The tape lines corresponded to each 94), (Tables 4,5). Bipolar surface electrodes with a 20 mm inter-electrode participant’s individually determined neutral distance were placed with the participant in a standing position. stance, ensuring a reproducible foot starting Electrode placement followed established protocols as described in position before initiating the step ascent action. Table 4, (91, 93, 94). 60 DATA COLLECTION; STUDIES I-IV KARI HUSETH 61 During the step ascent test, the stance foot was positioned in three A: start B: step conditions-neutral, pronated, and supinated-using individualized EVA wedges (35 Shore hardness), (100) to ensure comfort. Pronation was defined as a lateral lift, where the 5th digit was just off the ground, while supination was defined as a medial lift, where the 1st digit was just off the ground. Four trials were performed in each step condition for the right and left leg, respectively. Each participant then completed the task in a fixed sequence: (i) right neutral, (ii) left pronated, (iii) left neutral, (iv) right pronated, (v) right supinated, and (vi) left supinated. Standardized instructions were given to the participants prior to performing each step procedures. In addition, verbal cues were given on when to lift the stance foot up onto the bench and when to return the foot to the ground. A full step was defined as when the participant’s contralateral foot left the ground until the same foot was placed on the bench, with a time interval of approximately 1.5 seconds. Participants were instructed to lift one foot onto a bench and perform a single upward step, simulating a stair ascent. The bench was positioned FIGURE 20. The step condition showing the left limb in stance (to be analyzed) and the right limb performing the step maneuver in Study II. 0.325 m in front of the starting foot, with a height of 0.445 m. Participants were instructed to maintain a forward gaze at a fixed point 3.0 m ahead throughout the movement (Figure 20). NAVICULAR DROP TEST Each participant completed the step ascent in a standardized sequence To classify foot posture and define pronation level, the Navicular Drop of six stance conditions. Four trials were performed for each foot Test (NDT) was used as a clinical assessment tool in Study II. position for each leg. Standardized instructions and verbal cues guided NDT (101-103) is a static foot assessment used to evaluate the degree the participants during the task. A full step was defined from the moment of pronation by measuring the vertical displacement of the navicular the contralateral foot left the ground until it was placed on the bench, tuberosity from a neutral to a relaxed standing position (Figure 21). It lasting approximately 1.5 seconds. is designed to reflect sagittal plane movement of the navicular bone, Bipolar, bilateral EMG signals from the target muscles were recorded offering insight into foot posture. The test is performed with the patient (Tables 4, 5). Digital time markers were manually applied to define the standing in full weight-bearing, first positioning the foot in subtalar joint relevant phases of the step action, specifically from heel lift to flat foot neutral. The most prominent point of the navicular tuberosity is marked contact. To calculate the normalized EMG amplitude values (%MVIC), and its height from the floor is measured. The patient is then asked MVIC were initially performed for all muscle groups for 3–5 s using a to relax into their natural stance, and the new height is recorded. The specially designed test apparatus. difference between the two measurements represents the navicular 62 DATA COLLECTION; STUDIES I-IV KARI HUSETH 63 During the step ascent test, the stance foot was positioned in three A: start B: step conditions-neutral, pronated, and supinated-using individualized EVA wedges (35 Shore hardness), (100) to ensure comfort. Pronation was defined as a lateral lift, where the 5th digit was just off the ground, while supination was defined as a medial lift, where the 1st digit was just off the ground. Four trials were performed in each step condition for the right and left leg, respectively. Each participant then completed the task in a fixed sequence: (i) right neutral, (ii) left pronated, (iii) left neutral, (iv) right pronated, (v) right supinated, and (vi) left supinated. Standardized instructions were given to the participants prior to performing each step procedures. In addition, verbal cues were given on when to lift the stance foot up onto the bench and when to return the foot to the ground. A full step was defined as when the participant’s contralateral foot left the ground until the same foot was placed on the bench, with a time interval of approximately 1.5 seconds. Participants were instructed to lift one foot onto a bench and perform a single upward step, simulating a stair ascent. The bench was positioned FIGURE 20. The step condition showing the left limb in stance (to be analyzed) and the right limb performing the step maneuver in Study II. 0.325 m in front of the starting foot, with a height of 0.445 m. Participants were instructed to maintain a forward gaze at a fixed point 3.0 m ahead throughout the movement (Figure 20). NAVICULAR DROP TEST Each participant completed the step ascent in a standardized sequence To classify foot posture and define pronation level, the Navicular Drop of six stance conditions. Four trials were performed for each foot Test (NDT) was used as a clinical assessment tool in Study II. position for each leg. Standardized instructions and verbal cues guided NDT (101-103) is a static foot assessment used to evaluate the degree the participants during the task. A full step was defined from the moment of pronation by measuring the vertical displacement of the navicular the contralateral foot left the ground until it was placed on the bench, tuberosity from a neutral to a relaxed standing position (Figure 21). It lasting approximately 1.5 seconds. is designed to reflect sagittal plane movement of the navicular bone, Bipolar, bilateral EMG signals from the target muscles were recorded offering insight into foot posture. The test is performed with the patient (Tables 4, 5). Digital time markers were manually applied to define the standing in full weight-bearing, first positioning the foot in subtalar joint relevant phases of the step action, specifically from heel lift to flat foot neutral. The most prominent point of the navicular tuberosity is marked contact. To calculate the normalized EMG amplitude values (%MVIC), and its height from the floor is measured. The patient is then asked MVIC were initially performed for all muscle groups for 3–5 s using a to relax into their natural stance, and the new height is recorded. The specially designed test apparatus. difference between the two measurements represents the navicular 62 DATA COLLECTION; STUDIES I-IV KARI HUSETH 63 drop. The test can also be conducted in reverse or by marking the muscle activation through a mechanical bandpass fi lter (25-450 Hz). positions on an index card placed along the medial side of the foot. The signal was reamplifi ed with a baseline noise of 750 nV, an input Interpretation of results typically categorizes a drop of more than 5 mm impedance of >1 Gohm//20pF, and a common mode rejection ratio of as indicative of a supinated foot, 5–9 mm as neutral, and 10–15 mm as >80 dB. pronated. Kinematic and kinetic qualities were recorded using the OTS system from A B C Qualisys AB (Sweden) with 16 infrared Oqus 7 cameras synchronized with two Miqus video cameras sampling frequency of 250 Hz, and OPTIMA High-Performance Series force plates sampling frequency of 1000 Hz from Advanced Mechanical Technologies (USA) were used, with post-hoc processing in Visual 3D (HAS-Motion, Canada). The EMG and OTS systems were synchronized. In Study III, side-to-side diff erences between the aff ected and FIGURE 21. The navicular drop test. (A) Foot with the subtalar joint in neutral, with the navicular unaff ected limbs were assessed for EMG, kinematics, and kinetics tuberosity marked (red circle). (B) Foot in relaxed stance with the navicular tuberosity marked (red circle). (C) The diff erence in vertical distance (mm) between the two positions of the navicular during stance phase for both walking and running. Stance phase was tuberosity represents the navicular drop, which can be used as an indicator of a pronated or divided into three events: initial contact (IC), midstance (MS) and toe-off supinated foot posture. (TO) for further analysis. IC and TO were identifi ed from the force plate data as the time points when the foot fi rst contacted and subsequently In Studies I and II identical off -line signal processing of the EMG signals left the plate, respectively, while MS was defi ned as the instant when the was performed in the following order: (i) removing ECG components, COG passed over the COP (Figure 22). (ii) high pass fi ltering of all raw EMG signals using a 4th order zero- lag Butterworth fi lter with a cut-off frequency of 2 Hz, (iii) full-wave rectifi cation and low pass fi ltering using a symmetric moving RMS window (100ms time constant) and (iv) normalizing the fi ltered EMG amplitudes relative to peak EMG amplitude recorded during MVIC processed using identical fi ltering procedures. STUDIES III-IV In Studies III and IV, EMG data was recorded using the Delsys Trigno Research wireless system with Trigno Avanti electromyography FIGURE 22. Illustration of the stance phase events as defi ned in Studies III and IV, including initial sensors (Delsys Inc., USA). The sensors have built-in electrodes with an contact (IC), midstance (MS), and toe-off (TO). interelectrode spacing of 10 mm, the contact material is 99.9% silver. The system operated at a sampling frequency of 2000 Hz, recording 64 DATA COLLECTION; STUDIES I-IV KARI HUSETH 65 drop. The test can also be conducted in reverse or by marking the muscle activation through a mechanical bandpass fi lter (25-450 Hz). positions on an index card placed along the medial side of the foot. The signal was reamplifi ed with a baseline noise of 750 nV, an input Interpretation of results typically categorizes a drop of more than 5 mm impedance of >1 Gohm//20pF, and a common mode rejection ratio of as indicative of a supinated foot, 5–9 mm as neutral, and 10–15 mm as >80 dB. pronated. Kinematic and kinetic qualities were recorded using the OTS system from A B C Qualisys AB (Sweden) with 16 infrared Oqus 7 cameras synchronized with two Miqus video cameras sampling frequency of 250 Hz, and OPTIMA High-Performance Series force plates sampling frequency of 1000 Hz from Advanced Mechanical Technologies (USA) were used, with post-hoc processing in Visual 3D (HAS-Motion, Canada). The EMG and OTS systems were synchronized. In Study III, side-to-side diff erences between the aff ected and FIGURE 21. The navicular drop test. (A) Foot with the subtalar joint in neutral, with the navicular unaff ected limbs were assessed for EMG, kinematics, and kinetics tuberosity marked (red circle). (B) Foot in relaxed stance with the navicular tuberosity marked (red circle). (C) The diff erence in vertical distance (mm) between the two positions of the navicular during stance phase for both walking and running. Stance phase was tuberosity represents the navicular drop, which can be used as an indicator of a pronated or divided into three events: initial contact (IC), midstance (MS) and toe-off supinated foot posture. (TO) for further analysis. IC and TO were identifi ed from the force plate data as the time points when the foot fi rst contacted and subsequently In Studies I and II identical off -line signal processing of the EMG signals left the plate, respectively, while MS was defi ned as the instant when the was performed in the following order: (i) removing ECG components, COG passed over the COP (Figure 22). (ii) high pass fi ltering of all raw EMG signals using a 4th order zero- lag Butterworth fi lter with a cut-off frequency of 2 Hz, (iii) full-wave rectifi cation and low pass fi ltering using a symmetric moving RMS window (100ms time constant) and (iv) normalizing the fi ltered EMG amplitudes relative to peak EMG amplitude recorded during MVIC processed using identical fi ltering procedures. STUDIES III-IV In Studies III and IV, EMG data was recorded using the Delsys Trigno Research wireless system with Trigno Avanti electromyography FIGURE 22. Illustration of the stance phase events as defi ned in Studies III and IV, including initial sensors (Delsys Inc., USA). The sensors have built-in electrodes with an contact (IC), midstance (MS), and toe-off (TO). interelectrode spacing of 10 mm, the contact material is 99.9% silver. The system operated at a sampling frequency of 2000 Hz, recording 64 DATA COLLECTION; STUDIES I-IV KARI HUSETH 65 A B 4). Bipolar bilateral EMG signals were recorded from both the affected and unaffected sides. The elected normalization method for EMG was MVIC where participants performed four contractions of target muscles lasting for 6 s with 60 s resting periods between trials. At a self-selected speed, timed with TC Timer (Browner Timing System), over a 10-meter walkway with four centrally positioned force plates walking and running (averaging speed of 1.36 m/s and 2.51 m/s, respectively) were performed. Five valid foot strikes on the force plates were registered for both the right and left feet. STUDY IV Side-to-side differences in muscle activation, joint range of motion (ROM), joint moments, joint power, and support moment were examined during the stance phase of walking and running in 22 participants, approximately one year after an acute unilateral ATR. FIGURE 23: The EMG sensor application of the shank muscles: tibialis anterior (AT), medial gastrocnemius (GM), lateral gastrocnemius (GL) and soleus (SOL) and the marker model of 6 degrees of freedom (see also fi gure 14 for the marker model). The same methodological approach as in Study III was used for kinetic and kinematic data collection, including the use of force plates and segmentation of the stance phase into sub-phases for the EMG EMG activity was expressed as the mean percentage of %MVIC across calculations. EMG signals were normalized according to the same two stance sub-phases-initial contact to mid-stance (IC–MS) and mid- principles as in Study III (Figure 10). EMG activity was recorded using a stance to toe-off (MS–TO)-for the following target muscles: TA, GM, GL, full-surface electrode set-up applied to the TA, GM, GL, SOL, VM, GM, and SOL. Kinematic analysis included joint excursions, calculated as the EO and ES (Figure 24, table 4). total angular displacement (i.e., the diff erence between maximum and minimum joint angles) for the ankle, knee, and hip joints in the sagittal Kinetic variables included sagittal plane joint moments (Nm/kg) and plane, and for the ankle and hip joints in the frontal plane, separately joint power (W/kg) obtained at the discrete time events of IC, MS, and for each sub-phase. Kinetic analysis involved calculating mean joint TO respectively. moments (Nm/kg) for the same joints and planes, also segmented by sub-phases. Joint moments were further used to calculate the total support moment (SM) for each limb (104, 105). SM was defined as the sum of the EMG sensors were applied to AT, GM, GL and SOL muscles in a standing sagittal plane extensor moments obtained at the ankle, knee, and hip position, as outlined in the muscle application overview (Figure 23, Table respectively [Eq.1], to provide a measure of total limb support and inter- 66 DATA COLLECTION; STUDIES I-IV KARI HUSETH 67 A B 4). Bipolar bilateral EMG signals were recorded from both the affected and unaffected sides. The elected normalization method for EMG was MVIC where participants performed four contractions of target muscles lasting for 6 s with 60 s resting periods between trials. At a self-selected speed, timed with TC Timer (Browner Timing System), over a 10-meter walkway with four centrally positioned force plates walking and running (averaging speed of 1.36 m/s and 2.51 m/s, respectively) were performed. Five valid foot strikes on the force plates were registered for both the right and left feet. STUDY IV Side-to-side differences in muscle activation, joint range of motion (ROM), joint moments, joint power, and support moment were examined during the stance phase of walking and running in 22 participants, approximately one year after an acute unilateral ATR. FIGURE 23: The EMG sensor application of the shank muscles: tibialis anterior (AT), medial gastrocnemius (GM), lateral gastrocnemius (GL) and soleus (SOL) and the marker model of 6 degrees of freedom (see also fi gure 14 for the marker model). The same methodological approach as in Study III was used for kinetic and kinematic data collection, including the use of force plates and segmentation of the stance phase into sub-phases for the EMG EMG activity was expressed as the mean percentage of %MVIC across calculations. EMG signals were normalized according to the same two stance sub-phases-initial contact to mid-stance (IC–MS) and mid- principles as in Study III (Figure 10). EMG activity was recorded using a stance to toe-off (MS–TO)-for the following target muscles: TA, GM, GL, full-surface electrode set-up applied to the TA, GM, GL, SOL, VM, GM, and SOL. Kinematic analysis included joint excursions, calculated as the EO and ES (Figure 24, table 4). total angular displacement (i.e., the diff erence between maximum and minimum joint angles) for the ankle, knee, and hip joints in the sagittal Kinetic variables included sagittal plane joint moments (Nm/kg) and plane, and for the ankle and hip joints in the frontal plane, separately joint power (W/kg) obtained at the discrete time events of IC, MS, and for each sub-phase. Kinetic analysis involved calculating mean joint TO respectively. moments (Nm/kg) for the same joints and planes, also segmented by sub-phases. Joint moments were further used to calculate the total support moment (SM) for each limb (104, 105). SM was defined as the sum of the EMG sensors were applied to AT, GM, GL and SOL muscles in a standing sagittal plane extensor moments obtained at the ankle, knee, and hip position, as outlined in the muscle application overview (Figure 23, Table respectively [Eq.1], to provide a measure of total limb support and inter- 66 DATA COLLECTION; STUDIES I-IV KARI HUSETH 67 joint coordination and providing insight into compensatory movement using a 4th-order bidirectional Butterworth filter with a low-pass cut-off strategies that are not apparent when analyzing single joint moments at 10 Hz. in isolation. In Studies III and IV, the EQ-5D and Physical Activity Scale (PAS) SM=-(Mankle+Mknee+Mhip) [Eq.1] were included as PROMs to provide complementary information on participants’ perceived health-related quality of life and physical activity. A B EQ-5D The EQ-5D (106) is a standardized instrument used to measure self- reported health-related quality of life. It shows good construct and predictive validity, along with responsiveness, supporting its use for assessing health status in patients who have sustained traumatic limb injuries (107). EQ-5D includes five dimensions: mobility, self-care, usual activities, pain or discomfort, and anxiety or depression. Each dimension is assessed using five levels: no problems, slight problems, moderate problems, severe problems, and extreme problems. Patients indicate their current health status by selecting the statement that best describes their condition in each dimension. Each selection is represented by a single-digit score, and the five scores are combined to form a five-digit code. The code corresponds to a weighted score that summarizes an individual’s overall health status. Scores range from  -0.43 to 1.00, where  1.00 indicates perfect health  and  -0.43 reflects a health state FIGURE 24. The full EMG application of the target muscles; tibialis anterior (TA), medial considered worse than death. gastrocnemius (GM), lateral gastrocnemius (LG), soleus (SOL), vastus medialis (VM), medial gluteus (MG), external oblique (EO) and erector spinae (ES) and the marker model application of PHYSICAL ACTIVITY SCALE the 6 degrees of freedom (see also figure 14 for the marker model). The Physical Activity Scale (PAS), (108) is a self-reported questionnaire designed to assess the level of physical activity. Initially developed to The signal processing in Studies III and IV were identical. EMG data compare physiological outcomes between middle-aged individuals was filtered by a digital high pass filter of 5 Hz, followed by a 4th order and athletes of the same age, the PAS uses a six-point ordinal scale, Butterworth filter in Visual 3D, v. 2025.01.1, HAS-Motion, (Kingston, where a score of 1 indicates minimal physical activity and a score of Ontario, Canada). The data was then linearly detrended and smoothed 6 represents engagement in heavy physical activity. Although PAS has using a centered 30-ms root mean square (RMS) window to compute not been specifically validated for individuals after an ATR, patients who the linear envelope (Figure 12). The motion capture data was processed 68 DATA COLLECTION; STUDIES I-IV KARI HUSETH 69 joint coordination and providing insight into compensatory movement using a 4th-order bidirectional Butterworth filter with a low-pass cut-off strategies that are not apparent when analyzing single joint moments at 10 Hz. in isolation. In Studies III and IV, the EQ-5D and Physical Activity Scale (PAS) SM=-(Mankle+Mknee+Mhip) [Eq.1] were included as PROMs to provide complementary information on participants’ perceived health-related quality of life and physical activity. A B EQ-5D The EQ-5D (106) is a standardized instrument used to measure self- reported health-related quality of life. It shows good construct and predictive validity, along with responsiveness, supporting its use for assessing health status in patients who have sustained traumatic limb injuries (107). EQ-5D includes five dimensions: mobility, self-care, usual activities, pain or discomfort, and anxiety or depression. Each dimension is assessed using five levels: no problems, slight problems, moderate problems, severe problems, and extreme problems. Patients indicate their current health status by selecting the statement that best describes their condition in each dimension. Each selection is represented by a single-digit score, and the five scores are combined to form a five-digit code. The code corresponds to a weighted score that summarizes an individual’s overall health status. Scores range from  -0.43 to 1.00, where  1.00 indicates perfect health  and  -0.43 reflects a health state FIGURE 24. The full EMG application of the target muscles; tibialis anterior (TA), medial considered worse than death. gastrocnemius (GM), lateral gastrocnemius (LG), soleus (SOL), vastus medialis (VM), medial gluteus (MG), external oblique (EO) and erector spinae (ES) and the marker model application of PHYSICAL ACTIVITY SCALE the 6 degrees of freedom (see also figure 14 for the marker model). The Physical Activity Scale (PAS), (108) is a self-reported questionnaire designed to assess the level of physical activity. Initially developed to The signal processing in Studies III and IV were identical. EMG data compare physiological outcomes between middle-aged individuals was filtered by a digital high pass filter of 5 Hz, followed by a 4th order and athletes of the same age, the PAS uses a six-point ordinal scale, Butterworth filter in Visual 3D, v. 2025.01.1, HAS-Motion, (Kingston, where a score of 1 indicates minimal physical activity and a score of Ontario, Canada). The data was then linearly detrended and smoothed 6 represents engagement in heavy physical activity. Although PAS has using a centered 30-ms root mean square (RMS) window to compute not been specifically validated for individuals after an ATR, patients who the linear envelope (Figure 12). The motion capture data was processed 68 DATA COLLECTION; STUDIES I-IV KARI HUSETH 69 have sustained an ATR are often similar in terms of age ranges as those Studies I and II used conventional frequentist analyses-including originally studied. The PAS provides a general estimate of activity levels, repeated measures ANOVA and non-parametric tests-to evaluate group- which may be useful for evaluating functional recovery or physical level differences in EMG amplitude across foot postures, step phases, capacity in clinical and research setting. and test positions. These methods were considered appropriate for the controlled experimental designs but were limited in their ability to model STATISTICAL ANALYSIS temporal dynamics or fully account for inter-individual variability. Each of the four studies in this thesis employed statistical approaches STUDY I: tailored to their specific research aims and data characteristics (for To compare MVIC EMG activity between standing and supine body overview, see Table 6). Together, these diverse statistical approaches- positions across all target muscles, the Wilcoxon signed-rank test frequentist, Bayesian, and time-series-provided complementary was used, as most of the extracted data were not normally distributed insights. They enabled both structured group comparisons and more according to the Shapiro-Wilk test. Variability in MVIC EMG amplitude nuanced, temporally and probabilistically informed interpretations of was assessed by examining median values and quartile distributions for neuromechanical coordination following an ATR. each position, along with identification of outliers and extreme values. All statistical analyses were performed using SPSS, version 24. TABLE 6. Statistical Procedures and Software Applications utilized in Studies I-IV. STUDY II: Statistical method and data programs Study I Study II Study III Study IV Mean EMG amplitudes (%MVIC) were compared across neutral, Wilcoxon signed rank test ✔ ✔ ✔ pronated, and supinated stance positions for given target muscles on Multivariant normal Bayesian model ✔ both the right and left sides using Wilcoxon’s signed-rank test (p<0.05, Coefficient of variance (CV) ✔ two-tailed), as the Shapiro-Wilk test revealed that the majority of the data deviated significantly from a normal distribution. The neutral stance Statistical parametric mapping (SPM) ✔ served as the baseline condition for these comparisons. EMG amplitude Coefficient of quartile variance ✔ for each muscle was calculated as the mean of four trials and normalized SPSS v. 24 ✔ to the mean peak amplitude recorded during MVIC, expressed as a percentage of MVIC. All statistical analyses were conducted using IBM SPSS v. 28 ✔ SPSS Statistics, version 28. SPPS v. 30 ✔ ✔ R Foundation for Statistical Computing v. 4. 5. 0 with ✔ STUDY III: brms package v.2.21.0 Study III applied a multivariate Bayesian modeling framework to assess Matlab (Math works, Natick, USA) ✔ interlimb differences in terms of kinematics, kinetics, and EMG patterns G*Power v 3.1.9.7 ✔ ✔ during gait (109). This approach enabled simultaneous estimation of multiple outcomes and their correlations, while quantifying uncertainty 70 DATA COLLECTION; STUDIES I-IV KARI HUSETH 71 have sustained an ATR are often similar in terms of age ranges as those Studies I and II used conventional frequentist analyses-including originally studied. The PAS provides a general estimate of activity levels, repeated measures ANOVA and non-parametric tests-to evaluate group- which may be useful for evaluating functional recovery or physical level differences in EMG amplitude across foot postures, step phases, capacity in clinical and research setting. and test positions. These methods were considered appropriate for the controlled experimental designs but were limited in their ability to model STATISTICAL ANALYSIS temporal dynamics or fully account for inter-individual variability. Each of the four studies in this thesis employed statistical approaches STUDY I: tailored to their specific research aims and data characteristics (for To compare MVIC EMG activity between standing and supine body overview, see Table 6). Together, these diverse statistical approaches- positions across all target muscles, the Wilcoxon signed-rank test frequentist, Bayesian, and time-series-provided complementary was used, as most of the extracted data were not normally distributed insights. They enabled both structured group comparisons and more according to the Shapiro-Wilk test. Variability in MVIC EMG amplitude nuanced, temporally and probabilistically informed interpretations of was assessed by examining median values and quartile distributions for neuromechanical coordination following an ATR. each position, along with identification of outliers and extreme values. All statistical analyses were performed using SPSS, version 24. TABLE 6. Statistical Procedures and Software Applications utilized in Studies I-IV. STUDY II: Statistical method and data programs Study I Study II Study III Study IV Mean EMG amplitudes (%MVIC) were compared across neutral, Wilcoxon signed rank test ✔ ✔ ✔ pronated, and supinated stance positions for given target muscles on Multivariant normal Bayesian model ✔ both the right and left sides using Wilcoxon’s signed-rank test (p<0.05, Coefficient of variance (CV) ✔ two-tailed), as the Shapiro-Wilk test revealed that the majority of the data deviated significantly from a normal distribution. The neutral stance Statistical parametric mapping (SPM) ✔ served as the baseline condition for these comparisons. EMG amplitude Coefficient of quartile variance ✔ for each muscle was calculated as the mean of four trials and normalized SPSS v. 24 ✔ to the mean peak amplitude recorded during MVIC, expressed as a percentage of MVIC. All statistical analyses were conducted using IBM SPSS v. 28 ✔ SPSS Statistics, version 28. SPPS v. 30 ✔ ✔ R Foundation for Statistical Computing v. 4. 5. 0 with ✔ STUDY III: brms package v.2.21.0 Study III applied a multivariate Bayesian modeling framework to assess Matlab (Math works, Natick, USA) ✔ interlimb differences in terms of kinematics, kinetics, and EMG patterns G*Power v 3.1.9.7 ✔ ✔ during gait (109). This approach enabled simultaneous estimation of multiple outcomes and their correlations, while quantifying uncertainty 70 DATA COLLECTION; STUDIES I-IV KARI HUSETH 71 through posterior distributions. The use of 95% credible intervals To fit the models, six Markov chain Monte Carlo (MCMC) chains were allowed for probabilistic interpretation of the magnitude and direction run in parallel, yielding 6,000 post–warm-up iterations. Convergence of observed differences, aligning with the broader interpretive focus on was evaluated using the improved R-hat statistic (111). Default weakly variability and individual adaptation. This was particularly advantageous informative priors were applied; a Student’s t-distribution with 3 degrees given the moderate sample size and heterogeneity in neuromuscular of freedom for intercepts, a half-Student’s t-distribution for standard responses across participants. deviations, and a LKJ (Lewandowski–Kurowicka–Joe distribution) prior for covariance matrices. These priors introduce mild regularization, Based on the results from a previous study evaluating biomechanical slightly shrinking the posterior toward zero and thereby reducing the variables during walking, running, and hopping after an acute ATR (74), it was risk of type I and type M errors when dichotomizing credible intervals. estimated that a sample size of 38 patients would be required to detect significant side-to-side differences in lower extremity biomechanics (α = Quantitatively similar results can be obtained using penalized 0.05, statistical power = 80%) at 12 months post-injury. frequentist regression techniques such as ridge regression or LASSO. Model comparisons were conducted using the expected log pointwise All processed data were analyzed using a multivariate normal Bayesian predictive density (ELPD), (112). Side-to-side differences are presented model to assess within-subject differences between the affected and as posterior point estimates with corresponding 95% CrI. unaffected limbs. Point estimates and 95% credible intervals (CrI) were defined as the posterior median and the 2.5th and the 97.5th percentiles In addition, the coefficient of variation (CV) was calculated as the ratio of the posterior sample, respectively. In this model, posterior median and of the standard deviation to the mean to descriptively assess within- mean are not distinguishable; thus, descriptive statistics are reported subject variability in kinematic, kinetic, and EMG parameters (1, 113). as means and were generated using IBM SPSS Statistics (v. 30.0). Study IV employed Statistical Parametric Mapping (SPM) to compare Initially, separate multivariate models were fitted for kinetic, kinematic, continuous EMG%, joint angle (ROM), joint moment and joint power and electromyographic (EMG) data respectively, and then analyzed curves across the gait cycle. SPM allowed for time-resolved analysis independently for walking and running. Complete case data were used of entire waveforms, facilitating the detection of phase-specific for all models. As a sensitivity analysis, each outcome variable was also asymmetries that might be obscured by traditional pointwise modeled separately using univariate linear models that included only an comparisons. This method added a temporal dimension to the intercept and standard deviation. interpretation of segmental coordination. Six models were implemented in R (R Foundation for Statistical An a priori statistical power analysis was performed using G*Power v Computing), (version 4.5.0), (110) using the  BRMS  package (version 3.1.9.7 (114) to estimate the required sample size for a two-tailed paired 2.21.0) (111), which provides an interface to Stan for Bayesian inference. t-test. With an alpha level of 0.05, a planned sample size of n = 23, and Bayesian estimation was based on the joint posterior distribution, which an expected medium effect size (d = 0.53), the estimated power was allowed for quantification of uncertainty in all parameters, including 0.80, indicating that the study was sufficiently powered to detect within- average side-to-side differences, population standard deviations, and subject side-to-side effects. Temporal differences across the stance correlations between variables. phase were assessed using Statistical Parametric Mapping, package 72 DATA COLLECTION; STUDIES I-IV KARI HUSETH 73 through posterior distributions. The use of 95% credible intervals To fit the models, six Markov chain Monte Carlo (MCMC) chains were allowed for probabilistic interpretation of the magnitude and direction run in parallel, yielding 6,000 post–warm-up iterations. Convergence of observed differences, aligning with the broader interpretive focus on was evaluated using the improved R-hat statistic (111). Default weakly variability and individual adaptation. This was particularly advantageous informative priors were applied; a Student’s t-distribution with 3 degrees given the moderate sample size and heterogeneity in neuromuscular of freedom for intercepts, a half-Student’s t-distribution for standard responses across participants. deviations, and a LKJ (Lewandowski–Kurowicka–Joe distribution) prior for covariance matrices. These priors introduce mild regularization, Based on the results from a previous study evaluating biomechanical slightly shrinking the posterior toward zero and thereby reducing the variables during walking, running, and hopping after an acute ATR (74), it was risk of type I and type M errors when dichotomizing credible intervals. estimated that a sample size of 38 patients would be required to detect significant side-to-side differences in lower extremity biomechanics (α = Quantitatively similar results can be obtained using penalized 0.05, statistical power = 80%) at 12 months post-injury. frequentist regression techniques such as ridge regression or LASSO. Model comparisons were conducted using the expected log pointwise All processed data were analyzed using a multivariate normal Bayesian predictive density (ELPD), (112). Side-to-side differences are presented model to assess within-subject differences between the affected and as posterior point estimates with corresponding 95% CrI. unaffected limbs. Point estimates and 95% credible intervals (CrI) were defined as the posterior median and the 2.5th and the 97.5th percentiles In addition, the coefficient of variation (CV) was calculated as the ratio of the posterior sample, respectively. In this model, posterior median and of the standard deviation to the mean to descriptively assess within- mean are not distinguishable; thus, descriptive statistics are reported subject variability in kinematic, kinetic, and EMG parameters (1, 113). as means and were generated using IBM SPSS Statistics (v. 30.0). Study IV employed Statistical Parametric Mapping (SPM) to compare Initially, separate multivariate models were fitted for kinetic, kinematic, continuous EMG%, joint angle (ROM), joint moment and joint power and electromyographic (EMG) data respectively, and then analyzed curves across the gait cycle. SPM allowed for time-resolved analysis independently for walking and running. Complete case data were used of entire waveforms, facilitating the detection of phase-specific for all models. As a sensitivity analysis, each outcome variable was also asymmetries that might be obscured by traditional pointwise modeled separately using univariate linear models that included only an comparisons. This method added a temporal dimension to the intercept and standard deviation. interpretation of segmental coordination. Six models were implemented in R (R Foundation for Statistical An a priori statistical power analysis was performed using G*Power v Computing), (version 4.5.0), (110) using the  BRMS  package (version 3.1.9.7 (114) to estimate the required sample size for a two-tailed paired 2.21.0) (111), which provides an interface to Stan for Bayesian inference. t-test. With an alpha level of 0.05, a planned sample size of n = 23, and Bayesian estimation was based on the joint posterior distribution, which an expected medium effect size (d = 0.53), the estimated power was allowed for quantification of uncertainty in all parameters, including 0.80, indicating that the study was sufficiently powered to detect within- average side-to-side differences, population standard deviations, and subject side-to-side effects. Temporal differences across the stance correlations between variables. phase were assessed using Statistical Parametric Mapping, package 72 DATA COLLECTION; STUDIES I-IV KARI HUSETH 73 SPM1S in Matlab (MathWorks, Natick, USA). This time-continuous TABLE 8. Anthropometric characteristics of the lower extremities from Study II (n=12). statistical analysis method has been comprehensively described in Anthropometric Characteristics Participants previous work (115, 116). Descriptive statistics and  SM calculations  were Leg length R foot 89.9 (±7.3) conducted using  SPSS Statistics v 30.0  (IBM Corp., Armonk, USA). Leg length L foot 90.0 (±7.5) As the data was not normally distributed,  non-parametric Wilcoxon ND R foot 5.3 (±1.3) signed-rank testing was applied for paired comparisons for the SM of Mean mm (SD the affected and unaffected limbs. Both tests were implemented with an ND L foot 4.8 (±1.2) a-level of 0.05 (two-tailed). Data are presented as group mean and standard deviation (±SD). R = right; L = left; ND: navicular drop measure. For the processed EMG data, the coefficient of quartile variation (CQV) STUDIES III AND IV: was used to evaluate variability, providing a robust measure of dispersion suitable for non-normally distributed data (117, 118). This method was not Participants in Studies III (Table 9) and IV (Table 10) were recruited from the applied to kinematic and kinetic variables, as the presence of negative ongoing DUSTAR project (Diagnostic Ultrasonography for Sahlgrenska values rendered the CQV results uninterpretable. Academy, University of Gothenburg. Data collection was conducted approximately one year (+2 months) following the Achilles tendon injury. STUDY POPULATIONS A total of 37 participants were included in Study III, where EMG recording was applied to selected muscles of the shank. In Study IV, a subset of STUDIES I AND II: the final 22 participants underwent extended EMG recordings, which Participants in Studies I and II (Tables 7 and 8) were recruited as included muscles along the full biomechanical chain under investigation a convenience sample from the municipal area of Gothenburg, (Figure 25). either through Facebook advertisements or from the nursing and physiotherapy programs at the University of Gothenburg. STUDIES I AND II TABLE 7. Demographic data from Study I and II (n=12). Age (years) 33.3.(± 9.6) Height (cm) 173.6 (±7.8) Weight (kg) 71.6.(±11.3) BMI 23.5 (± 2.6) Data are presented as mean and standard deviation (SD). BMI = body mass index. FIGURE 25. Flow chart of participant inclusion in Studies III and IV. 74 DATA COLLECTION; STUDIES I-IV KARI HUSETH 75 SPM1S in Matlab (MathWorks, Natick, USA). This time-continuous TABLE 8. Anthropometric characteristics of the lower extremities from Study II (n=12). statistical analysis method has been comprehensively described in Anthropometric Characteristics Participants previous work (115, 116). Descriptive statistics and  SM calculations  were Leg length R foot 89.9 (±7.3) conducted using  SPSS Statistics v 30.0  (IBM Corp., Armonk, USA). Leg length L foot 90.0 (±7.5) As the data was not normally distributed,  non-parametric Wilcoxon ND R foot 5.3 (±1.3) signed-rank testing was applied for paired comparisons for the SM of Mean mm (SD the affected and unaffected limbs. Both tests were implemented with an ND L foot 4.8 (±1.2) a-level of 0.05 (two-tailed). Data are presented as group mean and standard deviation (±SD). R = right; L = left; ND: navicular drop measure. For the processed EMG data, the coefficient of quartile variation (CQV) STUDIES III AND IV: was used to evaluate variability, providing a robust measure of dispersion suitable for non-normally distributed data (117, 118). This method was not Participants in Studies III (Table 9) and IV (Table 10) were recruited from the applied to kinematic and kinetic variables, as the presence of negative ongoing DUSTAR project (Diagnostic Ultrasonography for Sahlgrenska values rendered the CQV results uninterpretable. Academy, University of Gothenburg. Data collection was conducted approximately one year (+2 months) following the Achilles tendon injury. STUDY POPULATIONS A total of 37 participants were included in Study III, where EMG recording was applied to selected muscles of the shank. In Study IV, a subset of STUDIES I AND II: the final 22 participants underwent extended EMG recordings, which Participants in Studies I and II (Tables 7 and 8) were recruited as included muscles along the full biomechanical chain under investigation a convenience sample from the municipal area of Gothenburg, (Figure 25). either through Facebook advertisements or from the nursing and physiotherapy programs at the University of Gothenburg. STUDIES I AND II TABLE 7. Demographic data from Study I and II (n=12). Age (years) 33.3.(± 9.6) Height (cm) 173.6 (±7.8) Weight (kg) 71.6.(±11.3) BMI 23.5 (± 2.6) Data are presented as mean and standard deviation (SD). BMI = body mass index. FIGURE 25. Flow chart of participant inclusion in Studies III and IV. 74 DATA COLLECTION; STUDIES I-IV KARI HUSETH 75 STUDY III TABLE 9. Participant demographics and patient reported outcome measurements score in Study III (n=37). Age (years) 47.4 (± 9.4) Height (meter) 1.79 (± 0.08) Weight (kg) 83.3 (± 16.6) BMI 26.9 (±4.9) PAS 4 (± 1.1) EQ-5D 0.7 (± 0.3) Data are presented as group mean and standard deviation (±SD). BMI = Body mass index; PAS= Physical activity scale (six-graded scale), self-reported level of physical activity (1.denoting extremely low physical activity and 6.denoting strenuous physical activity); EQ-5D self-reported score health-related quality of life (range 1- (-0.43), 1 = perfect health. -0.43 = worse than death. STUDY IV TABLE 10. Participant demographics and patient reported outcome measurements score in Study IV (n=22). Age (years) 48.0 (±10.9 ) Height (meter) 1.79 (± 0.08) Weight (kg) 83.3 (± 16.6) BMI 26.7 (±3.3) PAS 4.1 (± 1.2) EQ-5D 0.8 (± 0.2) Treatment: Surgery: No surgery: 14 participants 8 participants Data are presented as group mean and standard deviation (±SD). BMI = Body mass index; PAS = Physical activity scale (six-graded scale), self-reported level of physical activity (1 denoting extremely low physical activity and 6 denoting strenuous physical activity); EQ-5D self-reported score health-related quality of life (range 1- (-0.43), 1= perfect health. -0.43 = worse than death. 76 DATA COLLECTION; STUDIES I-IV KARI HUSETH 77 STUDY III TABLE 9. Participant demographics and patient reported outcome measurements score in Study III (n=37). Age (years) 47.4 (± 9.4) Height (meter) 1.79 (± 0.08) Weight (kg) 83.3 (± 16.6) BMI 26.9 (±4.9) PAS 4 (± 1.1) EQ-5D 0.7 (± 0.3) Data are presented as group mean and standard deviation (±SD). BMI = Body mass index; PAS= Physical activity scale (six-graded scale), self-reported level of physical activity (1.denoting extremely low physical activity and 6.denoting strenuous physical activity); EQ-5D self-reported score health-related quality of life (range 1- (-0.43), 1 = perfect health. -0.43 = worse than death. STUDY IV TABLE 10. Participant demographics and patient reported outcome measurements score in Study IV (n=22). Age (years) 48.0 (±10.9 ) Height (meter) 1.79 (± 0.08) Weight (kg) 83.3 (± 16.6) BMI 26.7 (±3.3) PAS 4.1 (± 1.2) EQ-5D 0.8 (± 0.2) Treatment: Surgery: No surgery: 14 participants 8 participants Data are presented as group mean and standard deviation (±SD). BMI = Body mass index; PAS = Physical activity scale (six-graded scale), self-reported level of physical activity (1 denoting extremely low physical activity and 6 denoting strenuous physical activity); EQ-5D self-reported score health-related quality of life (range 1- (-0.43), 1= perfect health. -0.43 = worse than death. 76 DATA COLLECTION; STUDIES I-IV KARI HUSETH 77 7. Summary of Results STUDY I Participants were recruited as a convenience sample from the Gothenburg area to compare two standardized test positions-supine and standing-for EMG normalization using MVIC. The aim was to determine whether body posture affects MVIC values for selected muscles in the trunk and lower extremities. No systematic differences in terms of EMG amplitudes were found when comparing the supine and standing positions for MVIC testing, suggesting that both postures are equally effective for normalizing muscle activity when it comes to group-level analyses (Figure 26). Bars show mean values; error bars indicate ±1 standard deviation. Muscles: TA = tibialis anterior, GlM = gluteus medius, AddL = adductor longus, RA = rectus abdominis, EO = external oblique, IO/ TrA = internal oblique/transversus abdominis. Substantial inter-individual variability was observed in muscle activation levels in both positions, indicating that normalization outcomes may differ across individuals regardless of the test posture (Figure 27). Muscles: tibialis anterior (TA), gluteus medius (GM), adductor longus (AddL), rectus abdominis (RA), external oblique (EO), and internal oblique/transversus abdominis (IO/TrA). R = right, L = left. Outliers are shown as circles (○); extreme values are marked with asterisks (*). Muscle activation did not differ significantly between the two positions (Figure 27). Say, who is this walking man? 👥👥 JAMES TAYLOR 78 SUMMARY OF RESULTS KARI HUSETH 79 7. Summary of Results STUDY I Participants were recruited as a convenience sample from the Gothenburg area to compare two standardized test positions-supine and standing-for EMG normalization using MVIC. The aim was to determine whether body posture affects MVIC values for selected muscles in the trunk and lower extremities. No systematic differences in terms of EMG amplitudes were found when comparing the supine and standing positions for MVIC testing, suggesting that both postures are equally effective for normalizing muscle activity when it comes to group-level analyses (Figure 26). Bars show mean values; error bars indicate ±1 standard deviation. Muscles: TA = tibialis anterior, GlM = gluteus medius, AddL = adductor longus, RA = rectus abdominis, EO = external oblique, IO/ TrA = internal oblique/transversus abdominis. Substantial inter-individual variability was observed in muscle activation levels in both positions, indicating that normalization outcomes may differ across individuals regardless of the test posture (Figure 27). Muscles: tibialis anterior (TA), gluteus medius (GM), adductor longus (AddL), rectus abdominis (RA), external oblique (EO), and internal oblique/transversus abdominis (IO/TrA). R = right, L = left. Outliers are shown as circles (○); extreme values are marked with asterisks (*). Muscle activation did not differ significantly between the two positions (Figure 27). Say, who is this walking man? 👥👥 JAMES TAYLOR 78 SUMMARY OF RESULTS KARI HUSETH 79 Figure 6 A r T _ O I L A r T _ O I R O E L µV O E R A R L FIGURE 27. Inter-individual variability (median ± interquartile range) in maximum EMG amplitude (µV) for selected lower-limb and trunk muscles during maximal voluntary isometric contractions (MVIC) performed in supine or standing positions. A R R L d d A STUDY II L This study investigated how foot kinematics-specifically supinated and L d d A R pronated positions compared with neutral affect muscle activation in selected lower extremity and trunk muscles. The foot position on the ipsilateral stance foot was manipulated, while the contralateral limb M l G L performed the step during a standardized vertical step maneuver. Participants were recruited from the same convenience sample as in M l G R Study I. Study II demonstrated that foot configuration had limited systematic A T L influence on neuromuscular activation during a single-step stair ascent, although some significant differences were observed in A individual muscles. Compared with the neutral baseline, foot supination T R and pronation resulted in significant changes in a few muscles but showed no systematic influence on trunk activation, whereas the lower extremity displayed more significant differences, yet these did 80 SUMMARY OF RESULTS KARI HUSETH 81 Mean EMG Values with SD: Supine vs Standing (All 12 Muscles) Supine Standing 1000 800 600 400 200 0 FIGURE 26. EMG amplitudes (µV) during maximal voluntary isometric contractions (MVIC) of selected muscles in supine (blue) and standing (orange) postures. E M G A m p l i t u d e ( m e a n ± S D ) Figure 6 A r T _ O I L A r T _ O I R O E L µV O E R A R L FIGURE 27. Inter-individual variability (median ± interquartile range) in maximum EMG amplitude (µV) for selected lower-limb and trunk muscles during maximal voluntary isometric contractions (MVIC) performed in supine or standing positions. A R R L d d A STUDY II L This study investigated how foot kinematics-specifically supinated and L d d A R pronated positions compared with neutral affect muscle activation in selected lower extremity and trunk muscles. The foot position on the ipsilateral stance foot was manipulated, while the contralateral limb M l G L performed the step during a standardized vertical step maneuver. Participants were recruited from the same convenience sample as in M l G R Study I. Study II demonstrated that foot configuration had limited systematic A T L influence on neuromuscular activation during a single-step stair ascent, although some significant differences were observed in A individual muscles. Compared with the neutral baseline, foot supination T R and pronation resulted in significant changes in a few muscles but showed no systematic influence on trunk activation, whereas the lower extremity displayed more significant differences, yet these did 80 SUMMARY OF RESULTS KARI HUSETH 81 Mean EMG Values with SD: Supine vs Standing (All 12 Muscles) Supine Standing 1000 800 600 400 200 0 FIGURE 26. EMG amplitudes (µV) during maximal voluntary isometric contractions (MVIC) of selected muscles in supine (blue) and standing (orange) postures. E M G A m p l i t u d e ( m e a n ± S D ) not reflect a substantial or systematic overall influence. Moreover, the high inter-individual variability in EMG data indicates that within-subject motor variability plays a crucial role in maintaining postural stability and task performance, particularly during functional activities exposed to perturbations. Right foot stance: Ipsilateral:  In the pronated position, the right EO (p=0.010) and TA (p=0.023) showed a higher activity than in neutral. In the supinated position, the right TA (p=0.004), PE (p=0.019), and SOL (p=0.005) showed a higher activity than in the neutral position. Contralateral:  In the pronated position, the left MU showed a higher activity than in the neutral position (p=0.034), (Figure 28). Left foot stance: Ipsilateral: In the supinated position, the left EO showed a higher activity than in the neutral position (p=0.023), while the left AddL (p=0.041) and SOL (p=0.050) showed lower activity than in the neutral position. Contralateral:  In the pronated position, the right MU showed a higher activity than in the neutral position (p=0.033), and in the supinated position, the right IO/TrA showed a higher activity than in the neutral position (p=0.023), (Figure 29). 82 SUMMARY OF RESULTS KARI HUSETH 83 FIGURE 28. Muscle activation assessed as mean EMG activity (SD) for the stance limb (right trunk and lower limb) and contralateral limb (left trunk and left gluteus medius) muscles during a standardized single-step stair ascent. IO/TrA = muscle internal oblique/transversus abdominis. The stance foot (right side) was placed in pronated, supinated, or neutral position (base line). Muscles showing signifi cant diff erences in activation compared with the neutral foot position: * pronated-right erector spinae, right tibialis anterior, left multifi dus; * supinated-right tibialis anterior, right soleus, n = 12. not reflect a substantial or systematic overall influence. Moreover, the high inter-individual variability in EMG data indicates that within-subject motor variability plays a crucial role in maintaining postural stability and task performance, particularly during functional activities exposed to perturbations. Right foot stance: Ipsilateral:  In the pronated position, the right EO (p=0.010) and TA (p=0.023) showed a higher activity than in neutral. In the supinated position, the right TA (p=0.004), PE (p=0.019), and SOL (p=0.005) showed a higher activity than in the neutral position. Contralateral:  In the pronated position, the left MU showed a higher activity than in the neutral position (p=0.034), (Figure 28). Left foot stance: Ipsilateral: In the supinated position, the left EO showed a higher activity than in the neutral position (p=0.023), while the left AddL (p=0.041) and SOL (p=0.050) showed lower activity than in the neutral position. Contralateral:  In the pronated position, the right MU showed a higher activity than in the neutral position (p=0.033), and in the supinated position, the right IO/TrA showed a higher activity than in the neutral position (p=0.023), (Figure 29). 82 SUMMARY OF RESULTS KARI HUSETH 83 FIGURE 28. Muscle activation assessed as mean EMG activity (SD) for the stance limb (right trunk and lower limb) and contralateral limb (left trunk and left gluteus medius) muscles during a standardized single-step stair ascent. IO/TrA = muscle internal oblique/transversus abdominis. The stance foot (right side) was placed in pronated, supinated, or neutral position (base line). Muscles showing signifi cant diff erences in activation compared with the neutral foot position: * pronated-right erector spinae, right tibialis anterior, left multifi dus; * supinated-right tibialis anterior, right soleus, n = 12. STUDY III A total of 37 participants were recruited from the ongoing DUSTAR project (Diagnostic Ultrasonography for the Choice of Treatment of Acute Achilles Tendon Rupture). Data collection took place approximately one year (+2 months) after the ATR. The study aimed to investigate limb-to-limb differences for lower extremity muscle activation, joint kinematics, and kinetics during the stance phase of walking and running. EMG was applied to selected shank muscles, while OTS was used to assess both kinematic and kinetic parameters in the affected as well as the unaffected limbs. Posterior point estimates indicated biomechanical alterations within the shank complex, with the strongest evidence for differences in lower-limb muscle activation and sagittal-plane kinematics. The kinematic data indicated relatively low inter-individual variability in ankle, knee, and ROM. In contrast, joint moments and EMG measures exhibited substantially greater inter-individual variability, suggesting more diverse neuromuscular and kinetic adaptation strategies across participants. The results below summarize these comparisons for two distinct periods of the stance phase: IC–MS and MS–TO. When assessing muscle activation across the stance-phase periods during walking and running, all examined muscles showed higher EMG activity in running, with the largest increments observed in the triceps surae muscle group (Figure 30). 84 SUMMARY OF RESULTS KARI HUSETH 85 FIGURE 29. Study II, left stance. Muscle activation assessed as mean EMG activity (SD) for the stance limb (left trunk and lower limb) and contralateral limb (right trunk and right gluteus medius) muscles during a standardized single-step stair ascent. IO/TrA = muscle internal oblique/transversus abdominis. The stance foot (left side) was placed in pronated, supinated, or neutral position (baseline). Muscles showing significant differences in activation compared with the neutral foot position: * pronated-right multifidus, * supinated-left external oblique, left adductor longus, left soleus, n = 12. STUDY III A total of 37 participants were recruited from the ongoing DUSTAR project (Diagnostic Ultrasonography for the Choice of Treatment of Acute Achilles Tendon Rupture). Data collection took place approximately one year (+2 months) after the ATR. The study aimed to investigate limb-to-limb differences for lower extremity muscle activation, joint kinematics, and kinetics during the stance phase of walking and running. EMG was applied to selected shank muscles, while OTS was used to assess both kinematic and kinetic parameters in the affected as well as the unaffected limbs. Posterior point estimates indicated biomechanical alterations within the shank complex, with the strongest evidence for differences in lower-limb muscle activation and sagittal-plane kinematics. The kinematic data indicated relatively low inter-individual variability in ankle, knee, and ROM. In contrast, joint moments and EMG measures exhibited substantially greater inter-individual variability, suggesting more diverse neuromuscular and kinetic adaptation strategies across participants. The results below summarize these comparisons for two distinct periods of the stance phase: IC–MS and MS–TO. When assessing muscle activation across the stance-phase periods during walking and running, all examined muscles showed higher EMG activity in running, with the largest increments observed in the triceps surae muscle group (Figure 30). 84 SUMMARY OF RESULTS KARI HUSETH 85 FIGURE 29. Study II, left stance. Muscle activation assessed as mean EMG activity (SD) for the stance limb (left trunk and lower limb) and contralateral limb (right trunk and right gluteus medius) muscles during a standardized single-step stair ascent. IO/TrA = muscle internal oblique/transversus abdominis. The stance foot (left side) was placed in pronated, supinated, or neutral position (baseline). Muscles showing significant differences in activation compared with the neutral foot position: * pronated-right multifidus, * supinated-left external oblique, left adductor longus, left soleus, n = 12. MG (3.4 EMG%, 95% CrI: 0.6 to 6.3) and LG (4.8 EMG%, 95% CrI: 2.3 to 7.6) compared to the unaffected side. Ankle sagittal ROM was reduced in the affected limb, with a posterior mean difference of -1.8° (95% CrI: -2.8° to -0.7°), (Figure 31). FIGURE 31. Walking. Posterior point estimates of between-limb differences during walking one year after Achilles tendon rupture for EMG % activation (GL= Gastrocnemius lateralis, GM = gastrocnemius medialis) and Ankle sagittal ROM in Nm/kg. IC-MS= initial contact to midstance, MS-TO = midstance to toe off, ROM = range of motion. Circles represent posterior means; horizontal lines represent 95% credible intervals (CrI). FIGURE 30. EMG% (%MVIC) recorded during walking and running by muscle and stance periods. Dumbbell plots show Walking and Running values for each stance period, with connecting lines and Δ labels indicating the difference (Walking − Running) in EMG %. Top panel: affected limb; Annotations indicate posterior mean (95% CrI) and posterior probability bottom panel: unaffected limb. of direction. Positive values indicate greater activation or excursion in the affected limb, negative values indicate reductions. Phases: IC–MS = initial contact to midstance; MS–TO = midstance During running, ankle sagittal ROM was reduced in MS -TO on the to toeoff. Muscles: TA = tibialis anterior; GM = gluteus medius; GL = affected side, with a mean difference of-4.1° (95% CrI: -5.8 to -2.5), gastrocnemius lateralis; SOL = soleus. along side a lower ankle sagittal moment (0.06 Nm/kg, 95% CrI: 0.01 to Inter-limb differences were observed in Study III. During walking, 0.11) compared with the unaffected side (Figure 32). posterior point estimates indicated greater LG activation in the affected limb during IC–MS, with a mean difference of 2.1 EMG% (95% CrI: 0.5 to 3.7). In MS–TO, the affected limb also showed higher activation in both 86 SUMMARY OF RESULTS KARI HUSETH 87 MG (3.4 EMG%, 95% CrI: 0.6 to 6.3) and LG (4.8 EMG%, 95% CrI: 2.3 to 7.6) compared to the unaffected side. Ankle sagittal ROM was reduced in the affected limb, with a posterior mean difference of -1.8° (95% CrI: -2.8° to -0.7°), (Figure 31). FIGURE 31. Walking. Posterior point estimates of between-limb differences during walking one year after Achilles tendon rupture for EMG % activation (GL= Gastrocnemius lateralis, GM = gastrocnemius medialis) and Ankle sagittal ROM in Nm/kg. IC-MS= initial contact to midstance, MS-TO = midstance to toe off, ROM = range of motion. Circles represent posterior means; horizontal lines represent 95% credible intervals (CrI). FIGURE 30. EMG% (%MVIC) recorded during walking and running by muscle and stance periods. Dumbbell plots show Walking and Running values for each stance period, with connecting lines and Δ labels indicating the difference (Walking − Running) in EMG %. Top panel: affected limb; Annotations indicate posterior mean (95% CrI) and posterior probability bottom panel: unaffected limb. of direction. Positive values indicate greater activation or excursion in the affected limb, negative values indicate reductions. Phases: IC–MS = initial contact to midstance; MS–TO = midstance During running, ankle sagittal ROM was reduced in MS -TO on the to toeoff. Muscles: TA = tibialis anterior; GM = gluteus medius; GL = affected side, with a mean difference of-4.1° (95% CrI: -5.8 to -2.5), gastrocnemius lateralis; SOL = soleus. along side a lower ankle sagittal moment (0.06 Nm/kg, 95% CrI: 0.01 to Inter-limb differences were observed in Study III. During walking, 0.11) compared with the unaffected side (Figure 32). posterior point estimates indicated greater LG activation in the affected limb during IC–MS, with a mean difference of 2.1 EMG% (95% CrI: 0.5 to 3.7). In MS–TO, the affected limb also showed higher activation in both 86 SUMMARY OF RESULTS KARI HUSETH 87 FIGURE 32. Running. Posterior estimates of between-limb differences during running one year after Achilles tendon rupture for ankle sagittal ROM in degrees and ankle sagittal moment in Nm/kg. ROM = range of motion, MS-TO = midstance to toe off. Dots represent posterior means; horizontal lines represent 95% CrI. Annotations indicate posterior mean (95% CrI) and posterior probability of direction. Positive values indicate greater ROM or moment in the affected limb, negative values indicate reductions. For variables in the frontal plane, no differences between the affected FIGURE 33. Inter-individual variability (coefficient of variation, CV%) in range of motion (ROM), and unaffected limbs were observed, neither during walking nor running. electromyography (EMG) activity, and joint moments during walking and running one year after an Achilles tendon rupture (ATR). Variability in joint moments, EMG activity, and ROM during walking and running was quantified using the coefficient of variation (CV). For Mean EMG activation profiles with variability are presented for the walking, variability was lowest in ankle, knee, and hip ROM (CV: 9-38%), TA, MG, LG, and SOL during the stance phase of walking and running higher in EMG activity (CV: 38-92%), and widest in joint moments (CV: (Figures 34-37). 9-900%), (z). During running, kinematic variability was greater (CV: 16-57%), EMG variability remained high (CV: 46-136%), and joint moments again showed the largest distribution (CV: 17-660%), (Figure 33). The very high CV values for joint moments reflect the mathematical definition of CV, where the standard deviation (nominator) is divided by the mean (denominator). When mean joint moments were close to zero, even modest absolute variability resulted in comparatively large CV values. 88 SUMMARY OF RESULTS KARI HUSETH 89 FIGURE 32. Running. Posterior estimates of between-limb differences during running one year after Achilles tendon rupture for ankle sagittal ROM in degrees and ankle sagittal moment in Nm/kg. ROM = range of motion, MS-TO = midstance to toe off. Dots represent posterior means; horizontal lines represent 95% CrI. Annotations indicate posterior mean (95% CrI) and posterior probability of direction. Positive values indicate greater ROM or moment in the affected limb, negative values indicate reductions. For variables in the frontal plane, no differences between the affected FIGURE 33. Inter-individual variability (coefficient of variation, CV%) in range of motion (ROM), and unaffected limbs were observed, neither during walking nor running. electromyography (EMG) activity, and joint moments during walking and running one year after an Achilles tendon rupture (ATR). Variability in joint moments, EMG activity, and ROM during walking and running was quantified using the coefficient of variation (CV). For Mean EMG activation profiles with variability are presented for the walking, variability was lowest in ankle, knee, and hip ROM (CV: 9-38%), TA, MG, LG, and SOL during the stance phase of walking and running higher in EMG activity (CV: 38-92%), and widest in joint moments (CV: (Figures 34-37). 9-900%), (z). During running, kinematic variability was greater (CV: 16-57%), EMG variability remained high (CV: 46-136%), and joint moments again showed the largest distribution (CV: 17-660%), (Figure 33). The very high CV values for joint moments reflect the mathematical definition of CV, where the standard deviation (nominator) is divided by the mean (denominator). When mean joint moments were close to zero, even modest absolute variability resulted in comparatively large CV values. 88 SUMMARY OF RESULTS KARI HUSETH 89 DriSvoeleus (n=36).tif DriSvoeleus_RUN (n=34).tif LoDgeglaa in LoDgeglaa in Sida 1 av 1 Sida 1 av 1 KARI_GRAPHS SPM N=37 KARI_GRAPHS SPM N=La3d7da ner alla Ladda ner alla Lateral Gastroc (n=36).tif Ägaren är dold 19 aug. 206 kB Namn Ägare Namn Ändringsdatum Filstorlek Sortera Ägare Ändringsdatum Filstorlek Sortera Lateral Gastroc_RUN (n=36)_SPM.tif Ägaren är dold 19 aug. 43 kB Lateral Gastroc (n=36)_SPM.tif Ägaren är dold 19 aug. 41 kB Lateral Gastroc_RUN (n=36).tif Ägaren är dold 19 aug. 187 kB Lateral Gastroc (n=36).tif Ägaren är dold 19 aug. 206 kB Medial Gastroc (n=35)_SPM.tif Ägaren är dold 19 aug. 41 kB Lateral Gastroc_RUN (n=36)_SPM.tif Ägaren är dold 19 aug. 43 kB Medial Gastroc (n=35).tif Ägaren är dold 19 aug. 239 kB Lateral Gastroc_RUN (n=36).tif Ägaren är dold 19 aug. 187 kB Medial Gastroc_RUN (n=35)_RUN.tif Ägaren är dold 19 aug. 41 kB Medial Gastroc (n=35)_SPM.tif Ägaren är dold 19 aug. 41 kB Medial Gastroc_RUN (n=35).tif Ägaren är dold 19 aug. 184 kB Medial Gastroc (n=35).tif Ägaren är dold 19 aug. 239 kB Soleus (n=36)_SPM.tif Ägaren är dold 19 aug. 38 kB Medial Gastroc_RUN (n=35)_RUN.tif Ägaren är dold 19 aug. 41 kB Soleus (n=36).tif Ägaren är dold 19 aug. 231 kB Medial Gastroc_RUN (n=35).tif Ägaren är dold 19 aug. 184 kB Soleus_RUN (n=34)_SPM.tif Ägaren är dold 19 aug. 39 kB Soleus (n=36)_SPM.tif Ägaren är dold 19 aug. 38 kB Soleus_RUN (n=34).tif Ägaren är dold 19 aug. 198 kB Soleus (n=36).tif Ägaren är dold 19 aug. 231 kB Tibialis Ant (n=35)_SPM.tif Ägaren är dold 19 aug. 38 kB Soleus_RUN (n=34)_SPM.tif Ägaren är dold 19 aug. 39 kB Tibialis Ant (n=35).tif Ägaren är dold 19 aug. 222 kB FIGURE 34. Muscle activation confi guration of Tibialis anterior (see capture Figure 37). Soleus_RUN (n=34).tif FIGURE 37. Muscle activÄagarteni oär dnold confi g19 uaugr. ation ofT eSstao D19rl8ive keB uutasn k.o sMtnadean normalized EMG activity (%MVIC) Testa Drive utan kostnad Tibialis Ant_RUN (n=35)_SPM.tiGfoogle Drive är en säker plats för alla dina 5ler Ägaren är dold 19 aug. Google D4r0iv keB är en säker plats för alla dina 5ler Tibialis Ant (n=35)_SPM.tif with inter-individSiudaal v/ a1riaÄgbareinl iätr dyold (±1 S19D au)g. for theK oam igffå3 n8ge ki Bdcag ted (blue) andS idua na/ff e1 cted (red) limbs.  For Kom igång i dag1 1Tibialis Ant_RUN (n=35).tif Ägaren är dold 19 aug. 182 kB stance phase in tibialis anterior (TA), medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL). Solid lines represent mean normalized EMG (%) across participants; shaded areas indicate inter-individual variability (±1 SD). The x-axis shows the stance phase of gait, from initial contact (IC) through midstance (MS) to toe-off (TO). STUDY IV A subset of 22 participants from the same cohort as Study III were included in Study IV. This study aimed to investigate side-to-side diff erences in muscle activation, ROM, joint power, joint moments, and FIGURE 35. Muscle activation confi guration of Medial gastrocnemius (see capture Figure 37). support moments during walking and running one year after an unilateral ATR. The analysis focused on segmental adaptations within the ankle– knee–hip complex and their distribution along the biomechanical chain up to the trunk. Bilateral EMG recordings were collected from eight muscles, as well as kinematic and kinetic measurements to assess coordination across the lower limb and trunk. EMG% values were consistently higher during running compared with walking, with the largest diff erences observed in the triceps surae (gastrocnemius medialis, gastrocnemius lateralis, and soleus) during early stance (Figures 38, 39). FIGURE 36. Muscle activation confi guration of Lateral gatrsocnemius (see capture Figure 37). 90 SUMMARY OF RESULTS KARI HUSETH 91 DriSvoeleus (n=36).tif DriSvoeleus_RUN (n=34).tif LoDgeglaa in LoDgeglaa in Sida 1 av 1 Sida 1 av 1 KARI_GRAPHS SPM N=37 KARI_GRAPHS SPM N=La3d7da ner alla Ladda ner alla Lateral Gastroc (n=36).tif Ägaren är dold 19 aug. 206 kB Namn Ägare Namn Ändringsdatum Filstorlek Sortera Ägare Ändringsdatum Filstorlek Sortera Lateral Gastroc_RUN (n=36)_SPM.tif Ägaren är dold 19 aug. 43 kB Lateral Gastroc (n=36)_SPM.tif Ägaren är dold 19 aug. 41 kB Lateral Gastroc_RUN (n=36).tif Ägaren är dold 19 aug. 187 kB Lateral Gastroc (n=36).tif Ägaren är dold 19 aug. 206 kB Medial Gastroc (n=35)_SPM.tif Ägaren är dold 19 aug. 41 kB Lateral Gastroc_RUN (n=36)_SPM.tif Ägaren är dold 19 aug. 43 kB Medial Gastroc (n=35).tif Ägaren är dold 19 aug. 239 kB Lateral Gastroc_RUN (n=36).tif Ägaren är dold 19 aug. 187 kB Medial Gastroc_RUN (n=35)_RUN.tif Ägaren är dold 19 aug. 41 kB Medial Gastroc (n=35)_SPM.tif Ägaren är dold 19 aug. 41 kB Medial Gastroc_RUN (n=35).tif Ägaren är dold 19 aug. 184 kB Medial Gastroc (n=35).tif Ägaren är dold 19 aug. 239 kB Soleus (n=36)_SPM.tif Ägaren är dold 19 aug. 38 kB Medial Gastroc_RUN (n=35)_RUN.tif Ägaren är dold 19 aug. 41 kB Soleus (n=36).tif Ägaren är dold 19 aug. 231 kB Medial Gastroc_RUN (n=35).tif Ägaren är dold 19 aug. 184 kB Soleus_RUN (n=34)_SPM.tif Ägaren är dold 19 aug. 39 kB Soleus (n=36)_SPM.tif Ägaren är dold 19 aug. 38 kB Soleus_RUN (n=34).tif Ägaren är dold 19 aug. 198 kB Soleus (n=36).tif Ägaren är dold 19 aug. 231 kB Tibialis Ant (n=35)_SPM.tif Ägaren är dold 19 aug. 38 kB Soleus_RUN (n=34)_SPM.tif Ägaren är dold 19 aug. 39 kB Tibialis Ant (n=35).tif Ägaren är dold 19 aug. 222 kB FIGURE 34. Muscle activation confi guration of Tibialis anterior (see capture Figure 37). Soleus_RUN (n=34).tif FIGURE 37. Muscle activÄagarteni oär dnold confi g19 uaugr. ation ofT eSstao D19rl8ive keB uutasn k.o sMtnadean normalized EMG activity (%MVIC) Testa Drive utan kostnad Tibialis Ant_RUN (n=35)_SPM.tiGfoogle Drive är en säker plats för alla dina 5ler Ägaren är dold 19 aug. Google D4r0iv keB är en säker plats för alla dina 5ler Tibialis Ant (n=35)_SPM.tif with inter-individSiudaal v/ a1riaÄgbareinl iätr dyold (±1 S19D au)g. for theK oam igffå3 n8ge ki Bdcag ted (blue) andS idua na/ff e1 cted (red) limbs.  For Kom igång i dag1 1Tibialis Ant_RUN (n=35).tif Ägaren är dold 19 aug. 182 kB stance phase in tibialis anterior (TA), medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL). Solid lines represent mean normalized EMG (%) across participants; shaded areas indicate inter-individual variability (±1 SD). The x-axis shows the stance phase of gait, from initial contact (IC) through midstance (MS) to toe-off (TO). STUDY IV A subset of 22 participants from the same cohort as Study III were included in Study IV. This study aimed to investigate side-to-side diff erences in muscle activation, ROM, joint power, joint moments, and FIGURE 35. Muscle activation confi guration of Medial gastrocnemius (see capture Figure 37). support moments during walking and running one year after an unilateral ATR. The analysis focused on segmental adaptations within the ankle– knee–hip complex and their distribution along the biomechanical chain up to the trunk. Bilateral EMG recordings were collected from eight muscles, as well as kinematic and kinetic measurements to assess coordination across the lower limb and trunk. EMG% values were consistently higher during running compared with walking, with the largest diff erences observed in the triceps surae (gastrocnemius medialis, gastrocnemius lateralis, and soleus) during early stance (Figures 38, 39). FIGURE 36. Muscle activation confi guration of Lateral gatrsocnemius (see capture Figure 37). 90 SUMMARY OF RESULTS KARI HUSETH 91 ankle joint power was lower near late stance (~88–90%, p=0.05), (Figure 44), reduced knee power was also observed in early stance (~8–10%, p=0.032), (Figure 45). Total support moment (SM) was signifi cantly lower in the aff ected limb at both initial contact (IC) and toe-off (TO), (p=0.001 for both), (Figure 46). Running: No signifi cant side-to-side diff erences were observed in muscle activation or joint power. However, ankle ROM was reduced in the aff ected limb during late stance (~77–100%, p=0.012), (Figure 43), and total SM was signifi cantly lower at TO (p=0.001), (Figure 47). FIGURE 38. Mean (±SD) normalized EMG activity during Walking across eight muscles: tibialis anterior (TA), medial gastrocnemius (MG), lateral gastrocnemius (LG), soleus (SOL), vastus medialis (VM), gluteus medius (GM), external oblique (EO), and erector spinae (ES). Results are Walking IC MS TO shown separately for early stance (IC–MS) and late stance (MS–TO), comparing the affected limb Knee Power (dark blue) to the unaffected limb (light blue). Ankle Power Ankle ROM SM (p=0.001) SM (p=0.001) GL 0% = IC 50% = MS 100% = TO Running IC MS TO SM (p=0.001) Ankle ROM 0 20 40 60 80 100 Stance Phase (%) 0% = IC 50% = MS 100% = TO FIGURE 40. Overview of the side-to-side diff erences in Study IV for joint kinematics, kinetics, and muscle activation one year after an Achilles tendon rupture (ATR). Sagittal plane joint kinematics, kinetics, and muscle activation during walking (top panel) and running (bottom panel). Vertical dashed lines indicate stance events (0% = initial contact [IC], 50% = midstance [MS], 100% = toe- FIGURE 39. Mean (±SD) normalized EMG activity during Running across eight muscles: tibialis off [TO]). Red arrows mark phases where total support moment (SM) was signifi cantly reduced anterior (TA), medial gastrocnemius (MG), lateral gastrocnemius (LG), soleus (SOL), vastus (p = 0.001). medialis (VM), gluteus medius (GM), external oblique (EO), and erector spinae (ES). Results are shown separately for early stance (IC–MS) and late stance (MS–TO), comparing the affected limb (dark red) to the unaffected limb (light red). Side-to-side differences observed in Study IV (Figure 40). During walking the affected limb showed significantly higher LG activation near the end of stance (~88–90%) compared with the unaffected limb (p=0.05), (Figure 41). Ankle ROM was significantly reduced in the affected limb during early stance (~17–20%, p=0.04), (Figure 42), and 92 SUMMARY OF RESULTS KARI HUSETH 93 ankle joint power was lower near late stance (~88–90%, p=0.05), (Figure 44), reduced knee power was also observed in early stance (~8–10%, p=0.032), (Figure 45). Total support moment (SM) was signifi cantly lower in the aff ected limb at both initial contact (IC) and toe-off (TO), (p=0.001 for both), (Figure 46). Running: No signifi cant side-to-side diff erences were observed in muscle activation or joint power. However, ankle ROM was reduced in the aff ected limb during late stance (~77–100%, p=0.012), (Figure 43), and total SM was signifi cantly lower at TO (p=0.001), (Figure 47). FIGURE 38. Mean (±SD) normalized EMG activity during Walking across eight muscles: tibialis anterior (TA), medial gastrocnemius (MG), lateral gastrocnemius (LG), soleus (SOL), vastus medialis (VM), gluteus medius (GM), external oblique (EO), and erector spinae (ES). Results are Walking IC MS TO shown separately for early stance (IC–MS) and late stance (MS–TO), comparing the affected limb Knee Power (dark blue) to the unaffected limb (light blue). Ankle Power Ankle ROM SM (p=0.001) SM (p=0.001) GL 0% = IC 50% = MS 100% = TO Running IC MS TO SM (p=0.001) Ankle ROM 0 20 40 60 80 100 Stance Phase (%) 0% = IC 50% = MS 100% = TO FIGURE 40. Overview of the side-to-side diff erences in Study IV for joint kinematics, kinetics, and muscle activation one year after an Achilles tendon rupture (ATR). Sagittal plane joint kinematics, kinetics, and muscle activation during walking (top panel) and running (bottom panel). Vertical dashed lines indicate stance events (0% = initial contact [IC], 50% = midstance [MS], 100% = toe- FIGURE 39. Mean (±SD) normalized EMG activity during Running across eight muscles: tibialis off [TO]). Red arrows mark phases where total support moment (SM) was signifi cantly reduced anterior (TA), medial gastrocnemius (MG), lateral gastrocnemius (LG), soleus (SOL), vastus (p = 0.001). medialis (VM), gluteus medius (GM), external oblique (EO), and erector spinae (ES). Results are shown separately for early stance (IC–MS) and late stance (MS–TO), comparing the affected limb (dark red) to the unaffected limb (light red). Side-to-side differences observed in Study IV (Figure 40). During walking the affected limb showed significantly higher LG activation near the end of stance (~88–90%) compared with the unaffected limb (p=0.05), (Figure 41). Ankle ROM was significantly reduced in the affected limb during early stance (~17–20%, p=0.04), (Figure 42), and 92 SUMMARY OF RESULTS KARI HUSETH 93 DriLvaeteral Gastroc (n=21).tif DriLvaeteral Gastroc (n=21)_SPM.tif LoDgeglaa in LoDgeglaa in Sida 1 av 1 KARI_GRAPHS SPM KARI_GRAPHS SPM Ladda ner alla Ladda ner alla Namn Ägare Namn Ändringsdatum Filstorlek Sortera Ägare Ändringsdatum Filstorlek Sortera N=37 Ägaren är dold N=37 19 aug. — Ägaren är dold 19 aug. — Lateral Gastroc (n=21)_SPM.tif Ägaren är dold Lateral Ga1s9t raoucg (.n=21)_SPM.tif 42 kB Ägaren är dold 19 aug. 42 kB Lateral Gastroc (n=21).tif Ägaren är dold Lateral Ga1s9t raoucg (.n=21).tif 221 kB Ägaren är dold 19 aug. 221 kB Medial Gastroc (n=21)_SPM.tif Ägaren är dold Medial Ga1s9tr aoucg (.n=21)_SPM.tif 41 kB Ägaren är dold 19 aug. 41 kB Medial Gastroc (n=21).tif Ägaren är dold Medial Ga1s9tr aoucg (.n=21).tif 213 kB Ägaren är dold 19 aug. 213 kB Sagittal Ankle Power_SPM.tif Ägaren är dold Sagittal An1k9l ea uPgo.wer_SPM.tif 46 kB Ägaren är dold 19 aug. 46 kB Sagittal Ankle Power.tif Ägaren är dold Sagittal An1k9l ea uPgo.wer.tif 75 kB Ägaren är dold 19 aug. 75 kB Sagittal Ankle Range of Motion_RUN_SPM.tif Ägaren är dold Sagittal An1k9l ea uRga.nge of Motion_RUN_SPM.t3if9 kB Ägaren är dold 19 aug. 39 kB Sagittal Ankle Range of Motion_RUN.tif Ägaren är dold Sagittal An1k9l ea uRga.nge of Motion_RUN.tif 99 kB Ägaren är dold 19 aug. 99 kB Sagittal Ankle Range of Motion_SPM.tif Ägaren är dold Sagittal An1k9l ea uRga.nge of Motion_SPM.tif 43 kB Ägaren är dold 19 aug. 43 kB Sagittal Ankle Range of Motion.tif Ägaren är dold Sagittal An1k9l ea uRga.nge of Motion.tif 103 kB Ägaren är dold 19 aug. 103 kB Sagittal Knee Power_SPM.tif FIGURE 41. Lateral gastrÄogarcen när deoldmiSuagistta l K(n1Ge9e a PuLgo.w)e r_SmPM.utif scle a43c kBtivity during the stancÄgaeren äpr dohldase o19f a ugw. alking 43 kB FIGURE 43. Ankle sagittal ROM measured during the stance phase of running one year after Testa Drive utan kostnad Testa Drive utan kostnad Sagittal Knee Power.tif one year after Achilles tenÄgdareon änr d olrd upSagtittual rKne1e9e a. Pu goL.weer.tifft panel: 122 kB Ägaren är dold 19 aug. 122 kBGoogle Drive är en säker plats för alla dina 5ler Google Drive är en säker plats för alla dina 5ler Sida / 1 Kom ig ånMg i daeg an normalized EMG activity (%MVIC) with Achilles tendon rupture. Left panel: Mean ankle ROM in degrees (°) with inter-individual variability 1 Sida 1 / 1 Kom igång i dag inter-individual variability (±1 SD) for the aff ected (blue) and unaff ected (red) limbs. Right panel: (±1 SD) for the aff ected (blue) and unaff ected (red) limbs. Right panel: One-dimensional paired One-dimensional paired t-test (SPM) comparing aff ected and unaff ected sides. The black curve t-test (SPM) comparing aff ected and unaff ected sides. The black curve represents the t-statistic represents the t-statistic across stance, with the critical threshold (α = 0.05) shown by the dashed across stance, with the critical threshold (α = 0.05) shown by the dashed red line. Signifi cant red line. Signifi cant diff erence between aff ected and unaff ected limbs was seen in later part of diff erences between aff ected and unaff cetd limbs were observed in the late part of stance. stance. FIGURE 42. Ankle sagittal ROM measured during the stance phase of walking one year after an FIGURE 44. Sagittal ankle joint power measured during the stance phase of walking one year Achilles tendon rupture. Left panel: Mean ankle ROM in degrees (°) with inter-individual variability after Achilles tendon rupture. Left panel: Mean ankle power (W/kg) with inter-individual variability (±1 SD) for the aff ected (blue) and unaff ected (red) limbs.  Right panel: One-dimensional paired (±1 SD) for the aff ected (blue) and unaff ected (red) limbs.  Right panel: One-dimensional paired t-test comparing aff ected and unaff ected sides. The black curve represents the t-statistic across t-test (SPM) comparing aff ected and unaff ected sides. The black curve represents the t-statistic stance, with the critical threshold (α = 0.05) shown by the dashed red line. Signifi cant diff erences across stance, with the red dashed line marking the signifi cance threshold (α = 0.05). Signifi cant between aff ected and unaff ected limbs were seen in the early part of stance. diff erences between aff ected and unaff ected limbs were seen in the later part of stance. 94 SUMMARY OF RESULTS KARI HUSETH 95 DriLvaeteral Gastroc (n=21).tif DriLvaeteral Gastroc (n=21)_SPM.tif LoDgeglaa in LoDgeglaa in Sida 1 av 1 KARI_GRAPHS SPM KARI_GRAPHS SPM Ladda ner alla Ladda ner alla Namn Ägare Namn Ändringsdatum Filstorlek Sortera Ägare Ändringsdatum Filstorlek Sortera N=37 Ägaren är dold N=37 19 aug. — Ägaren är dold 19 aug. — Lateral Gastroc (n=21)_SPM.tif Ägaren är dold Lateral Ga1s9t raoucg (.n=21)_SPM.tif 42 kB Ägaren är dold 19 aug. 42 kB Lateral Gastroc (n=21).tif Ägaren är dold Lateral Ga1s9t raoucg (.n=21).tif 221 kB Ägaren är dold 19 aug. 221 kB Medial Gastroc (n=21)_SPM.tif Ägaren är dold Medial Ga1s9tr aoucg (.n=21)_SPM.tif 41 kB Ägaren är dold 19 aug. 41 kB Medial Gastroc (n=21).tif Ägaren är dold Medial Ga1s9tr aoucg (.n=21).tif 213 kB Ägaren är dold 19 aug. 213 kB Sagittal Ankle Power_SPM.tif Ägaren är dold Sagittal An1k9l ea uPgo.wer_SPM.tif 46 kB Ägaren är dold 19 aug. 46 kB Sagittal Ankle Power.tif Ägaren är dold Sagittal An1k9l ea uPgo.wer.tif 75 kB Ägaren är dold 19 aug. 75 kB Sagittal Ankle Range of Motion_RUN_SPM.tif Ägaren är dold Sagittal An1k9l ea uRga.nge of Motion_RUN_SPM.t3if9 kB Ägaren är dold 19 aug. 39 kB Sagittal Ankle Range of Motion_RUN.tif Ägaren är dold Sagittal An1k9l ea uRga.nge of Motion_RUN.tif 99 kB Ägaren är dold 19 aug. 99 kB Sagittal Ankle Range of Motion_SPM.tif Ägaren är dold Sagittal An1k9l ea uRga.nge of Motion_SPM.tif 43 kB Ägaren är dold 19 aug. 43 kB Sagittal Ankle Range of Motion.tif Ägaren är dold Sagittal An1k9l ea uRga.nge of Motion.tif 103 kB Ägaren är dold 19 aug. 103 kB Sagittal Knee Power_SPM.tif FIGURE 41. Lateral gastrÄogarcen när deoldmiSuagistta l K(n1Ge9e a PuLgo.w)e r_SmPM.utif scle a43c kBtivity during the stancÄgaeren äpr dohldase o19f a ugw. alking 43 kB FIGURE 43. Ankle sagittal ROM measured during the stance phase of running one year after Testa Drive utan kostnad Testa Drive utan kostnad Sagittal Knee Power.tif one year after Achilles tenÄgdareon änr d olrd upSagtittual rKne1e9e a. Pu goL.weer.tifft panel: 122 kB Ägaren är dold 19 aug. 122 kBGoogle Drive är en säker plats för alla dina 5ler Google Drive är en säker plats för alla dina 5ler Sida / 1 Kom ig ånMg i daeg an normalized EMG activity (%MVIC) with Achilles tendon rupture. Left panel: Mean ankle ROM in degrees (°) with inter-individual variability 1 Sida 1 / 1 Kom igång i dag inter-individual variability (±1 SD) for the aff ected (blue) and unaff ected (red) limbs. Right panel: (±1 SD) for the aff ected (blue) and unaff ected (red) limbs. Right panel: One-dimensional paired One-dimensional paired t-test (SPM) comparing aff ected and unaff ected sides. The black curve t-test (SPM) comparing aff ected and unaff ected sides. The black curve represents the t-statistic represents the t-statistic across stance, with the critical threshold (α = 0.05) shown by the dashed across stance, with the critical threshold (α = 0.05) shown by the dashed red line. Signifi cant red line. Signifi cant diff erence between aff ected and unaff ected limbs was seen in later part of diff erences between aff ected and unaff cetd limbs were observed in the late part of stance. stance. FIGURE 42. Ankle sagittal ROM measured during the stance phase of walking one year after an FIGURE 44. Sagittal ankle joint power measured during the stance phase of walking one year Achilles tendon rupture. Left panel: Mean ankle ROM in degrees (°) with inter-individual variability after Achilles tendon rupture. Left panel: Mean ankle power (W/kg) with inter-individual variability (±1 SD) for the aff ected (blue) and unaff ected (red) limbs.  Right panel: One-dimensional paired (±1 SD) for the aff ected (blue) and unaff ected (red) limbs.  Right panel: One-dimensional paired t-test comparing aff ected and unaff ected sides. The black curve represents the t-statistic across t-test (SPM) comparing aff ected and unaff ected sides. The black curve represents the t-statistic stance, with the critical threshold (α = 0.05) shown by the dashed red line. Signifi cant diff erences across stance, with the red dashed line marking the signifi cance threshold (α = 0.05). Signifi cant between aff ected and unaff ected limbs were seen in the early part of stance. diff erences between aff ected and unaff ected limbs were seen in the later part of stance. 94 SUMMARY OF RESULTS KARI HUSETH 95 FIGURE 45. Sagittal knee joint power generation during the stance phase of walking one year after Achilles tendon rupture. Left panel: Mean knee power (W/kg) with inter-individual variability (±1 SD) for the aff ected (blue) and unaff ected (red) limbs. Right panel: One-dimensional paired FIGURE 47. Support moment (Nm/kg) during running for aff ected (green) and unaff ected (grey) t-test (SPM) comparing aff ected and unaff ected sides. The black curve represents the t-statistic limbs (n = 22). Bars represent mean values at initial contact (IC), midstance (MS), and toe-off (TO). across stance, with the red dashed line marking the signifi cance threshold (α = 0.05). Signifi cant Error bars indicate SD. Asterisks (*) mark signifi cant diff erences between limbs (p<0.05). diff erences between aff ected and unaff ected limbs were seen in the early part of stance. Total support moment (SM): Motor variability The coeffi cient of quartile variation (CQV) revealed distinct patterns of Although individual joint moments calculations did not diff er signifi cantly inter-individual variability across muscles, stance phases, and limbs between aff ected and unaff ected limbs, the calculated support moments during both walking and running (Figures 48, 49). Across-gait modes, did. In walking, signifi cant diff erences were found at IC (p<0.001) and TO ankle plantar fl exors displayed more consistent activation profi les, (p<0.001), (Figure 46), and in running at TO (p<0.001), (Figure 47), with while proximal and trunk muscles demonstrated greater inter-individual lower values in the aff ected limb compared with the unaff ected. variability. Support moment walking FIGURE 46. Support moment (Nm/kg) during walking for aff ected (green) and unaff ected (grey) limbs (n = 22). Bars represent mean values at initial contact (IC), midstance (MS), and toe-off (TO). Error bars indicate SD. Asterisks (*) mark signifi cant diff erences between limbs (p<0.05). 96 SUMMARY OF RESULTS KARI HUSETH 97 FIGURE 45. Sagittal knee joint power generation during the stance phase of walking one year after Achilles tendon rupture. Left panel: Mean knee power (W/kg) with inter-individual variability (±1 SD) for the aff ected (blue) and unaff ected (red) limbs. Right panel: One-dimensional paired FIGURE 47. Support moment (Nm/kg) during running for aff ected (green) and unaff ected (grey) t-test (SPM) comparing aff ected and unaff ected sides. The black curve represents the t-statistic limbs (n = 22). Bars represent mean values at initial contact (IC), midstance (MS), and toe-off (TO). across stance, with the red dashed line marking the signifi cance threshold (α = 0.05). Signifi cant Error bars indicate SD. Asterisks (*) mark signifi cant diff erences between limbs (p<0.05). diff erences between aff ected and unaff ected limbs were seen in the early part of stance. Total support moment (SM): Motor variability The coeffi cient of quartile variation (CQV) revealed distinct patterns of Although individual joint moments calculations did not diff er signifi cantly inter-individual variability across muscles, stance phases, and limbs between aff ected and unaff ected limbs, the calculated support moments during both walking and running (Figures 48, 49). Across-gait modes, did. In walking, signifi cant diff erences were found at IC (p<0.001) and TO ankle plantar fl exors displayed more consistent activation profi les, (p<0.001), (Figure 46), and in running at TO (p<0.001), (Figure 47), with while proximal and trunk muscles demonstrated greater inter-individual lower values in the aff ected limb compared with the unaff ected. variability. Support moment walking FIGURE 46. Support moment (Nm/kg) during walking for aff ected (green) and unaff ected (grey) limbs (n = 22). Bars represent mean values at initial contact (IC), midstance (MS), and toe-off (TO). Error bars indicate SD. Asterisks (*) mark signifi cant diff erences between limbs (p<0.05). 96 SUMMARY OF RESULTS KARI HUSETH 97 FIGURE 48. Coefficient of quartile variation (CQV, %) for affected and unaffected limbs during FIGURE 49. Coefficient of quartile variation (CQV, %) for affected and unaffected limbs during walking, shown separately for eight muscles: tibialis anterior, medial gastrocnemius, lateral running, shown separately for eight muscles: tibialis anterior, medial gastrocnemius, lateral gastrocnemius, soleus, vastus medialis, gluteus medius, external oblique, and erector spinae. gastrocnemius, soleus, vastus medialis, gluteus medius, external oblique, and erector spinae. CQV values are presented for early stance (IC–MS = initial contact to midstance) and late stance CQV values are presented for early stance (initial contact to midstance, IC–MS) and late stance (MS–TO = midstance to toe-off). Blue lines represent the affected limb and yellow lines the (midstance to toe-off, MS–TO). Blue lines represent the affected limb and yellow lines the unaffected limb. unaffected limb. 98 SUMMARY OF RESULTS KARI HUSETH 99 FIGURE 48. Coefficient of quartile variation (CQV, %) for affected and unaffected limbs during FIGURE 49. Coefficient of quartile variation (CQV, %) for affected and unaffected limbs during walking, shown separately for eight muscles: tibialis anterior, medial gastrocnemius, lateral running, shown separately for eight muscles: tibialis anterior, medial gastrocnemius, lateral gastrocnemius, soleus, vastus medialis, gluteus medius, external oblique, and erector spinae. gastrocnemius, soleus, vastus medialis, gluteus medius, external oblique, and erector spinae. CQV values are presented for early stance (IC–MS = initial contact to midstance) and late stance CQV values are presented for early stance (initial contact to midstance, IC–MS) and late stance (MS–TO = midstance to toe-off). Blue lines represent the affected limb and yellow lines the (midstance to toe-off, MS–TO). Blue lines represent the affected limb and yellow lines the unaffected limb. unaffected limb. 98 SUMMARY OF RESULTS KARI HUSETH 99 8. Discussion The main contributions of this thesis are first, the demonstration that EMG normalization is reliable and second, the observation that changes in foot configuration are mainly absorbed locally rather than propagated proximally. After an Achilles tendon rupture, neuromechanical adaptations remain largely localized to the lower leg. Persistent ankle deficits and occasional knee compensations occur, but overall gait patterns resemble normative kinematics. The discussion section is organized around four identified knowledge gaps: 1) methodological, 2) methodological/biomechanical, 3) clinical, and 4) integrative (Figure 50), each of which are addressed in the following sections. Knowledge gap IV Integration gap – Distribution of adaptations from feet up to trunk (Study IV) Knowledge gap III Clinical gap – ATR stance-phase mechanics (Study III) Knowledge gap II Methodological/biomechanical gap – foot posture (Study II) It’s very hard in the beginning to understand that the whole idea Knowledge gap IMethodological gap – is not to beat the other runners. Eventually, you learn that the EMG normalization competition is against the little voice inside you that wants you (Study I) to quit. FIGURE 50. A visualization of the four knowledge gaps identified in this thesis and how they 👥👥 GEORGE SHEEHAN correspond to Studies I–IV. EMG = electromyography 100 DISCUSSION KARI HUSETH 101 8. Discussion The main contributions of this thesis are first, the demonstration that EMG normalization is reliable and second, the observation that changes in foot configuration are mainly absorbed locally rather than propagated proximally. After an Achilles tendon rupture, neuromechanical adaptations remain largely localized to the lower leg. Persistent ankle deficits and occasional knee compensations occur, but overall gait patterns resemble normative kinematics. The discussion section is organized around four identified knowledge gaps: 1) methodological, 2) methodological/biomechanical, 3) clinical, and 4) integrative (Figure 50), each of which are addressed in the following sections. Knowledge gap IV Integration gap – Distribution of adaptations from feet up to trunk (Study IV) Knowledge gap III Clinical gap – ATR stance-phase mechanics (Study III) Knowledge gap II Methodological/biomechanical gap – foot posture (Study II) It’s very hard in the beginning to understand that the whole idea Knowledge gap IMethodological gap – is not to beat the other runners. Eventually, you learn that the EMG normalization competition is against the little voice inside you that wants you (Study I) to quit. FIGURE 50. A visualization of the four knowledge gaps identified in this thesis and how they 👥👥 GEORGE SHEEHAN correspond to Studies I–IV. EMG = electromyography 100 DISCUSSION KARI HUSETH 101 Methodological Gap – EMG normalization (STUDY I) muscle activity, with limited effects on trunk muscles except the erector (130) Normalization of surface EMG signals to MVIC values is essential for spinae . In population data, foot pronation showed an association between-participants comparability, yet differences in testing posture with back pain in women, though no consistent links were found overall (131) could influence the outcome (98). Posture can alter muscle activation . magnitude and recruitment strategy because supine positions remove Evidence also suggests limited distal–proximal coupling (132-135). No load-bearing and postural stabilization demands, while upright positions correlation was found between the foot position and pelvic or lumbar engage trunk and lower-limb muscles in a more functional manner. motion during standing (33). Bilateral EMG recordings showed that In Study I, upright and supine MVIC testing for lower-limb and trunk extensive pronation or supination did not alter activity in trunk muscles (29) muscles yielded comparable values with showed excellent test–retest such as latissimus dorsi, pectoralis major, or rectus abdominis . No reliability (ICC = 0.80–0.90), indicating that EMG normalization is association was detected between hyperpronation and severity of biomechanically stable and reproducible across positions, when nonspecific low back pain (34). protocols are applied consistently. Nonetheless, upright testing more Changes in foot kinematics have been associated with overuse in closely reflects the neuromuscular demands of dynamic locomotion gait, and foot orthoses are sometimes recommended for other than and may therefore provide greater ecological validity for gait-related foot problems/symptoms only (136, 137), including the knee, hip, and research. back, although evidence is still limited. These patterns, together with indications of neuromuscular action, postulate a relationship between Methodological/Biomechanical Gap – Foot posture (Study II) foot function and proximal control. In neurological terms, sensory input The biomechanical chain model proposes that distal changes, such from plantar mechanoreceptors can affect multi-joint coordination, as altered foot posture, can propagate proximally through mechanical potentially eliciting trunk responses within 100–200 ms (138, 139). and neural coupling (119-122). Manipulating stance foot posture (neutral, pronation, supination) during a vertical step maneuver altered muscle Altered foot posture primarily affects lower-leg mechanics and muscle activation in the lower extremity to some extent, while less effects on activity, with limited and inconsistent effects on pelvic alignment or the trunk and no systematic influences were seen. Distal alignment trunk function. While neural pathways such as plantar sensory input changes were largely absorbed locally, with lower-leg muscles more may link distal and proximal segments, current evidence indicates that responsive to foot kinematics than trunk muscles. most adaptations are absorbed locally, suggesting only modest distal– proximal coupling. Kinematic and neuromuscular links between foot posture and proximal segments have been demonstrated (123-125). Calcaneal eversion alters Clinical Gap – ACHILLES TENDON RUPTURE stance-phase mechanics pelvic alignment through shank and thigh rotation (121, 126). Pelvic motion (STUDY III) changes occur with altered foot positions or insole inclination, though The Achilles tendon can store and release elastic energy during spinal posture remains unaffected (127, 128). Trunk kinematics adapt to locomotion (51, 52), while simultaneously being capable of transmitting foot inclination during prolonged standing without changes in muscle forces up to eight times the body weight during running (56). Its function thickness (129). Foot pronation and supination modulate lower-limb reduces the metabolic cost of overground movement and enhances 102 DISCUSSION KARI HUSETH 103 Methodological Gap – EMG normalization (STUDY I) muscle activity, with limited effects on trunk muscles except the erector (130) Normalization of surface EMG signals to MVIC values is essential for spinae . In population data, foot pronation showed an association between-participants comparability, yet differences in testing posture with back pain in women, though no consistent links were found overall (131) could influence the outcome (98). Posture can alter muscle activation . magnitude and recruitment strategy because supine positions remove Evidence also suggests limited distal–proximal coupling (132-135). No load-bearing and postural stabilization demands, while upright positions correlation was found between the foot position and pelvic or lumbar engage trunk and lower-limb muscles in a more functional manner. motion during standing (33). Bilateral EMG recordings showed that In Study I, upright and supine MVIC testing for lower-limb and trunk extensive pronation or supination did not alter activity in trunk muscles (29) muscles yielded comparable values with showed excellent test–retest such as latissimus dorsi, pectoralis major, or rectus abdominis . No reliability (ICC = 0.80–0.90), indicating that EMG normalization is association was detected between hyperpronation and severity of biomechanically stable and reproducible across positions, when nonspecific low back pain (34). protocols are applied consistently. Nonetheless, upright testing more Changes in foot kinematics have been associated with overuse in closely reflects the neuromuscular demands of dynamic locomotion gait, and foot orthoses are sometimes recommended for other than and may therefore provide greater ecological validity for gait-related foot problems/symptoms only (136, 137), including the knee, hip, and research. back, although evidence is still limited. These patterns, together with indications of neuromuscular action, postulate a relationship between Methodological/Biomechanical Gap – Foot posture (Study II) foot function and proximal control. In neurological terms, sensory input The biomechanical chain model proposes that distal changes, such from plantar mechanoreceptors can affect multi-joint coordination, as altered foot posture, can propagate proximally through mechanical potentially eliciting trunk responses within 100–200 ms (138, 139). and neural coupling (119-122). Manipulating stance foot posture (neutral, pronation, supination) during a vertical step maneuver altered muscle Altered foot posture primarily affects lower-leg mechanics and muscle activation in the lower extremity to some extent, while less effects on activity, with limited and inconsistent effects on pelvic alignment or the trunk and no systematic influences were seen. Distal alignment trunk function. While neural pathways such as plantar sensory input changes were largely absorbed locally, with lower-leg muscles more may link distal and proximal segments, current evidence indicates that responsive to foot kinematics than trunk muscles. most adaptations are absorbed locally, suggesting only modest distal– proximal coupling. Kinematic and neuromuscular links between foot posture and proximal segments have been demonstrated (123-125). Calcaneal eversion alters Clinical Gap – ACHILLES TENDON RUPTURE stance-phase mechanics pelvic alignment through shank and thigh rotation (121, 126). Pelvic motion (STUDY III) changes occur with altered foot positions or insole inclination, though The Achilles tendon can store and release elastic energy during spinal posture remains unaffected (127, 128). Trunk kinematics adapt to locomotion (51, 52), while simultaneously being capable of transmitting foot inclination during prolonged standing without changes in muscle forces up to eight times the body weight during running (56). Its function thickness (129). Foot pronation and supination modulate lower-limb reduces the metabolic cost of overground movement and enhances 102 DISCUSSION KARI HUSETH 103 propulsion (2, 54). Achilles tendon rupture disrupts these functions, while or trunk. One year after an Achilles tendon rupture, individuals thus typically causing chronic tendon elongation, more or less regardless presented task- and phase-specific neuromechanical asymmetries of surgical or non-surgical treatment (140), accompanied by reduced during walking, primarily at the ankle. This might reflect altered tendon stiffness (141, 142), and persistent plantar flexor weakness (50, 143, 144). mechanics and disrupted activation patterns, with a potential shift from monoarticular to biarticular muscle use, reduced activation One year after an Achilles tendon rupture, walking was characterized by variability, and redistribution of joint power across the lower limb. increased gastrocnemius activation and reduced ankle sagittal ROM in Such pattern supports a segmentally constrained model in which the affected shank compared with the contralateral side. During running, coupling is strongest between the adjacent segments and diminishes ankle ROM was likewise reduced and accompanied by attenuated with distance from the site of impairment. Contralateral contributions plantar flexor moments, although no clear inter-limb differences in and preserved proximal function may reduce the need for widespread terms of EMG were observed. Despite these shank-level asymmetries, reorganization. the overall gait patterns resembled normative kinematics, probably reflecting compensatory strategies (145). EMG amplitudes and joint RETHINKING THE BIOMECHANICAL CHAIN: ABSORPTIVE moments displayed greater variability than kinematic measures. These COUPLING MODEL findings confirm persistent deficits in triceps surae function and tendon stiffness, consistent with previous reports (73, 78, 146). Compensation The integrated findings from Studies I–IV support an alternative view to strategies were found to vary, with some participants increasing the traditional Biomechanical Chain Model. In this Absorptive Coupling knee extensor moments to shift propulsion proximally, while others Model, mechanical effects are most pronounced at the site of change maintained symmetrical knee kinetics, despite ankle impairments as and in adjacent segments, while they progressively diminish at more discussed in detail above. proximally levels (Figure 51). Neural control mechanisms act in parallel to preserve overall coordination, limiting the spread of distal alterations Integration Gap – Distribution of adaptations from feet up to trunk throughout the chain. Distal changes can influence proximal function, (Study IV) yet the magnitude, direction, and consequences depend on task If the biomechanical chain operated as a rigidly linked system, distal demands, individual variability, and the nervous system’s compensatory impairments like ATR would be expected to cause systematic proximal capacity. The biomechanical chain is therefore neither a rigid sequence adaptations. However, the extent of such propagation depends on both nor a purely local phenomenon, but a dynamic, probabilistic interaction mechanical attenuation-loss of force transmission with distance-and system in which mechanical influences are absorbed along the way central nervous system strategies, which may buffer local disturbances. and coordination emerges from the interplay of mechanical and neural factors. In the present investigation, ATR-related adaptations were predominantly localized to the distal limb and expressed as side- to-side differences from the foot upward. The affected limb showed persistent ankle deficits and occasional compensations at the knee, whereas no consistent asymmetries were observed at the hip, pelvis, 104 DISCUSSION KARI HUSETH 105 propulsion (2, 54). Achilles tendon rupture disrupts these functions, while or trunk. One year after an Achilles tendon rupture, individuals thus typically causing chronic tendon elongation, more or less regardless presented task- and phase-specific neuromechanical asymmetries of surgical or non-surgical treatment (140), accompanied by reduced during walking, primarily at the ankle. This might reflect altered tendon stiffness (141, 142), and persistent plantar flexor weakness (50, 143, 144). mechanics and disrupted activation patterns, with a potential shift from monoarticular to biarticular muscle use, reduced activation One year after an Achilles tendon rupture, walking was characterized by variability, and redistribution of joint power across the lower limb. increased gastrocnemius activation and reduced ankle sagittal ROM in Such pattern supports a segmentally constrained model in which the affected shank compared with the contralateral side. During running, coupling is strongest between the adjacent segments and diminishes ankle ROM was likewise reduced and accompanied by attenuated with distance from the site of impairment. Contralateral contributions plantar flexor moments, although no clear inter-limb differences in and preserved proximal function may reduce the need for widespread terms of EMG were observed. Despite these shank-level asymmetries, reorganization. the overall gait patterns resembled normative kinematics, probably reflecting compensatory strategies (145). EMG amplitudes and joint RETHINKING THE BIOMECHANICAL CHAIN: ABSORPTIVE moments displayed greater variability than kinematic measures. These COUPLING MODEL findings confirm persistent deficits in triceps surae function and tendon stiffness, consistent with previous reports (73, 78, 146). Compensation The integrated findings from Studies I–IV support an alternative view to strategies were found to vary, with some participants increasing the traditional Biomechanical Chain Model. In this Absorptive Coupling knee extensor moments to shift propulsion proximally, while others Model, mechanical effects are most pronounced at the site of change maintained symmetrical knee kinetics, despite ankle impairments as and in adjacent segments, while they progressively diminish at more discussed in detail above. proximally levels (Figure 51). Neural control mechanisms act in parallel to preserve overall coordination, limiting the spread of distal alterations Integration Gap – Distribution of adaptations from feet up to trunk throughout the chain. Distal changes can influence proximal function, (Study IV) yet the magnitude, direction, and consequences depend on task If the biomechanical chain operated as a rigidly linked system, distal demands, individual variability, and the nervous system’s compensatory impairments like ATR would be expected to cause systematic proximal capacity. The biomechanical chain is therefore neither a rigid sequence adaptations. However, the extent of such propagation depends on both nor a purely local phenomenon, but a dynamic, probabilistic interaction mechanical attenuation-loss of force transmission with distance-and system in which mechanical influences are absorbed along the way central nervous system strategies, which may buffer local disturbances. and coordination emerges from the interplay of mechanical and neural factors. In the present investigation, ATR-related adaptations were predominantly localized to the distal limb and expressed as side- to-side differences from the foot upward. The affected limb showed persistent ankle deficits and occasional compensations at the knee, whereas no consistent asymmetries were observed at the hip, pelvis, 104 DISCUSSION KARI HUSETH 105 Study IV Walking showed higher GL activity, reduced ankle/knee power, and lower support moment in the affected limb; running showed reduced ankle ROM and support moment at TO. Variability was low in plantar flexors but high in proximal and trunk muscles, with greater asymmetry in running. Study III Credible shank-level differences emerged in muscle activation of gastrocnemius and sagittal kinematics. KSintuedmya tIiVcs were consistent, while EMG and joint From a mechanical perspective, distal changes-whether experimentally mWomaleknintsg vsahroiewde md hoirgeh werid GelLy aacctriovsitsy i,n rdeidvuicdeuda lasn. kle/knee power, and lower support moment in the affected limb; induced (Study II) or related to ATR (Studies III–IV) produced the most Srtundnyi nIgI showed reduced ankle ROM and support moment consistent eff ects both locally and in neighboring segments. The impact Faoto Tt Opo. sVtuareia mbiolidtyu lwataesd ldoiwst ainl mpluasnctlaer aflcetxivoartsi obnu tt oh isgohm ien exptreonxti,m wahl ialen de ftfreucntks omnu tsrculneks, mwuitshc lgerse watere a msyimnomr.e Htryig ihn generated at foot strike is progressively attenuated with increasing inrtuenr-niinndgi.vidual variability highlights the role of within- subject motor variability in stable performance. distance from its point of origin, likely due to joint compliance, soft Study III SCtureddyi bIle shank-level differences emerged in muscle tissue deformation, and energy dissipation within multi-joint muscle– Saucptivnaet aionnd osfta gnadsitnrgo cMneVmIiCus parnodv sidaegdit tcaol mkipnaermabalteic s. tendon units. From a  neural control perspective, the CNS uses motor nKorimneamliaztaitciso nw. eHreo wcoenvseirs,t ehnigt,h w inhtieler- EinMdiGvi daunadl jvoainrita bility inmdoicmaetenst so vuatcroiemd ems omrea yw didifefleyr across individuals. abundance to achieve the same outcome through multiple coordination Study II strategies, allowing local adjustments to preserve proximal stability and Foot posture modulated distal muscle activation to some limiting widespread reorganization. extent, while effects on trunk muscles were minor. High inter-individual variability highlights the role of within- subject motor variability in stable performance. This integrated interpretationexplains why trunk adaptations were minimal Study I in both experimental and clinical contexts, and why compensations were Supine and standing MVICs provided comparable normalization. However, high inter-individual variability often managed locally or through contralateral limb contributions. The indicates outcomes may differ across individuals. Absorptive Coupling Model can be considered a possible reframing of the FIGURE 51. The absorptive coupling model of the biomechanical chain. In this model, local biomechanical chain, emphasizing its selective and context-dependent and adjacent segments exhibit the strongest mechanical coupling, while proximal infl uence nature rather than a deterministic cascade. Such an interpretation progressively diminishes, with neural control maintaining overall coordination. GL = lateral appears consistent with contemporary motor control theory, with regards gastrocnemius, TO = toe-off , EMG = electromyography, MVIC =maximum voluntary isometric contraction. to variability as a functional property supporting adaptability in complex and unpredictable environments (25, 147, 148). Three principles underpin the absorptive coupling model: METHODOLOGICAL CONSIDERATIONS • Neuromuscular variability is intrinsic: activation patterns varied markedly between individuals across all tasks, consistent with LIMITATIONS, VALIDITY, AND RELIABILITY OF EMG AND MOTION motor abundance. This variability explains why some participants CAPTURE SYSTEM (MOCAP) adopted knee-dominant propulsion after ATR, while others did Surface EMG measures the spatial summation of MUAPs at the muscle not, and why foot posture changes had inconsistent trunk eff ects. surface (149). Because these potentials must travel through layers of Adaptations are segment-specifi c: the largest eff ects occurred tissue before reaching the electrodes, the recorded signal becomes • (10) locally and in adjacent segments, with clear attenuation along the attenuated . Electrode placement is therefore critical and should be chain. performed by one or only a few trained investigators strictly adhering to standardized protocols as was done in the present study (92). Individual • Task and phase specifi city matters: distal–proximal eff ects were anatomical variations, however, means that few people exactly match the more pronounced in walking than running, likely due to stance- confi gurations illustrated in anatomical atlases. In addition, movement phase duration, reliance on push-off , and Achilles tendon elastic of electrode wires, skin motion relative to the underlying muscle, and energy storage and return. 106 DISCUSSION KARI HUSETH 107 Study IV Walking showed higher GL activity, reduced ankle/knee power, and lower support moment in the affected limb; running showed reduced ankle ROM and support moment at TO. Variability was low in plantar flexors but high in proximal and trunk muscles, with greater asymmetry in running. Study III Credible shank-level differences emerged in muscle activation of gastrocnemius and sagittal kinematics. KSintuedmya tIiVcs were consistent, while EMG and joint From a mechanical perspective, distal changes-whether experimentally mWomaleknintsg vsahroiewde md hoirgeh werid GelLy aacctriovsitsy i,n rdeidvuicdeuda lasn. kle/knee power, and lower support moment in the affected limb; induced (Study II) or related to ATR (Studies III–IV) produced the most Srtundnyi nIgI showed reduced ankle ROM and support moment consistent eff ects both locally and in neighboring segments. The impact Faoto Tt Opo. sVtuareia mbiolidtyu lwataesd ldoiwst ainl mpluasnctlaer aflcetxivoartsi obnu tt oh isgohm ien exptreonxti,m wahl ialen de ftfreucntks omnu tsrculneks, mwuitshc lgerse watere a msyimnomr.e Htryig ihn generated at foot strike is progressively attenuated with increasing inrtuenr-niinndgi.vidual variability highlights the role of within- subject motor variability in stable performance. distance from its point of origin, likely due to joint compliance, soft Study III SCtureddyi bIle shank-level differences emerged in muscle tissue deformation, and energy dissipation within multi-joint muscle– Saucptivnaet aionnd osfta gnadsitnrgo cMneVmIiCus parnodv sidaegdit tcaol mkipnaermabalteic s. tendon units. From a  neural control perspective, the CNS uses motor nKorimneamliaztaitciso nw. eHreo wcoenvseirs,t ehnigt,h w inhtieler- EinMdiGvi daunadl jvoainrita bility inmdoicmaetenst so vuatcroiemd ems omrea yw didifefleyr across individuals. abundance to achieve the same outcome through multiple coordination Study II strategies, allowing local adjustments to preserve proximal stability and Foot posture modulated distal muscle activation to some limiting widespread reorganization. extent, while effects on trunk muscles were minor. High inter-individual variability highlights the role of within- subject motor variability in stable performance. This integrated interpretationexplains why trunk adaptations were minimal Study I in both experimental and clinical contexts, and why compensations were Supine and standing MVICs provided comparable normalization. However, high inter-individual variability often managed locally or through contralateral limb contributions. The indicates outcomes may differ across individuals. Absorptive Coupling Model can be considered a possible reframing of the FIGURE 51. The absorptive coupling model of the biomechanical chain. In this model, local biomechanical chain, emphasizing its selective and context-dependent and adjacent segments exhibit the strongest mechanical coupling, while proximal infl uence nature rather than a deterministic cascade. Such an interpretation progressively diminishes, with neural control maintaining overall coordination. GL = lateral appears consistent with contemporary motor control theory, with regards gastrocnemius, TO = toe-off , EMG = electromyography, MVIC =maximum voluntary isometric contraction. to variability as a functional property supporting adaptability in complex and unpredictable environments (25, 147, 148). Three principles underpin the absorptive coupling model: METHODOLOGICAL CONSIDERATIONS • Neuromuscular variability is intrinsic: activation patterns varied markedly between individuals across all tasks, consistent with LIMITATIONS, VALIDITY, AND RELIABILITY OF EMG AND MOTION motor abundance. This variability explains why some participants CAPTURE SYSTEM (MOCAP) adopted knee-dominant propulsion after ATR, while others did Surface EMG measures the spatial summation of MUAPs at the muscle not, and why foot posture changes had inconsistent trunk eff ects. surface (149). Because these potentials must travel through layers of Adaptations are segment-specifi c: the largest eff ects occurred tissue before reaching the electrodes, the recorded signal becomes • (10) locally and in adjacent segments, with clear attenuation along the attenuated . Electrode placement is therefore critical and should be chain. performed by one or only a few trained investigators strictly adhering to standardized protocols as was done in the present study (92). Individual • Task and phase specifi city matters: distal–proximal eff ects were anatomical variations, however, means that few people exactly match the more pronounced in walking than running, likely due to stance- confi gurations illustrated in anatomical atlases. In addition, movement phase duration, reliance on push-off , and Achilles tendon elastic of electrode wires, skin motion relative to the underlying muscle, and energy storage and return. 106 DISCUSSION KARI HUSETH 107 crosstalk from adjacent muscles can all affect the signal amplitude (149). making them unreliable for precise motion assessment (156). These The presence of electrodes, wires, sensors, and tape may also alter a results emphasize that while sagittal-plane measures, especially participant’s natural motor pattern during task performance. flexion/extension, are reasonably robust, frontal and transverse plane kinematics are more susceptible to soft tissue artefacts and marker The interpretation of sEMG should therefore be guided by careful displacement and should therefore be interpreted with caution. adherence to protocol and further an awareness of its limitations (91). Despite these constraints, several studies support its value in terms Across all acquisition systems in the gait laboratory, high-quality results of biomechanical research (124–126). For example, a study on paraspinal depend on a sound understanding of musculoskeletal anatomy, strict muscle fatigue concluded that there is convincing evidence for sEMG’s adherence to protocol, and meticulous handling of instrumentation. utility for such assessments (150). Mitchell et al. reported intra-session Transparent reporting of methods and data-processing algorithms is reliability for trunk muscle sEMG, with ICCs ranging from 0.80 to 0.90 therefore essential for reproducibility and for meaningful interpretation in able-bodied controls; in individuals with spinal cord injury, (151) and (92), particularly when studying the biomechanical chain from the foot to Bogey et al. found surface electrodes to be as repeatable as fine- trunk. wire electrodes during gait analysis for the soleus muscle (152). Taken together, these findings indicate that when applied using standardized ETHICAL CONSIDERATIONS protocols and interpreted cautiously, sEMG can yield reliable, meaningful This thesis adheres to the principles of the Declaration of Helsinki (157) insights into neuromuscular function, particularly for evaluating muscle and the European Code of Conduct for Research Integrity (158), upholding activation patterns and fatigue. reliability, honesty, respect, and accountability throughout the entire research process. Similarly, the reliability of MOCAP has been assessed extensively. A primary limitation arises from soft tissue artefacts caused by muscle The positive outcomes of all four studies were considered to outweigh contraction, gravity, skin deformation, or sliding of markers attached to any potential discomfort experienced by the study participants. Given the skin (153). Concurrent validity is highest in the sagittal plane (correlation that the methodologies employed were non-invasive, the burden placed coefficient >0.7), lower in the coronal plane (0.5-0.6), and lowest in the on participants can be considered minimal. transverse plane (≤0.4), (154). Validation studies often compare MOCAP with radiostereometric analysis (RSA), in which tantalum markers are Biomechanical data collection often requires participants to wear less implanted into cortical bone and tracked by stereoradiographs (154, 155). clothing (e.g., shorts and a top), which may be perceived as somewhat The strongest correlations between these measurement modalities uncomfortable or awkward by some individuals. The data collection have been reported for hip flexion and abduction, while rotational process can be time-consuming, as sEMG electrode placement measures show poorer agreement (155). requires thorough skin preparation, which may occasionally cause minor skin irritation. No participants reported complaints, and no dropouts Fändriks et al. compared three marker sets against RSA for knee motion occurred due to personal issues related to the method during the analysis (156). Although sagittal-plane flexion–extension measures were laboratory investigations. Also, the isometric contractions performed consistent across all sets, each underestimated true skeletal motion. during the sEMG session can cause some muscle soreness during one Frontal and transverse plane measures were highly inconsistent, 108 DISCUSSION KARI HUSETH 109 crosstalk from adjacent muscles can all affect the signal amplitude (149). making them unreliable for precise motion assessment (156). These The presence of electrodes, wires, sensors, and tape may also alter a results emphasize that while sagittal-plane measures, especially participant’s natural motor pattern during task performance. flexion/extension, are reasonably robust, frontal and transverse plane kinematics are more susceptible to soft tissue artefacts and marker The interpretation of sEMG should therefore be guided by careful displacement and should therefore be interpreted with caution. adherence to protocol and further an awareness of its limitations (91). Despite these constraints, several studies support its value in terms Across all acquisition systems in the gait laboratory, high-quality results of biomechanical research (124–126). For example, a study on paraspinal depend on a sound understanding of musculoskeletal anatomy, strict muscle fatigue concluded that there is convincing evidence for sEMG’s adherence to protocol, and meticulous handling of instrumentation. utility for such assessments (150). Mitchell et al. reported intra-session Transparent reporting of methods and data-processing algorithms is reliability for trunk muscle sEMG, with ICCs ranging from 0.80 to 0.90 therefore essential for reproducibility and for meaningful interpretation in able-bodied controls; in individuals with spinal cord injury, (151) and (92), particularly when studying the biomechanical chain from the foot to Bogey et al. found surface electrodes to be as repeatable as fine- trunk. wire electrodes during gait analysis for the soleus muscle (152). Taken together, these findings indicate that when applied using standardized ETHICAL CONSIDERATIONS protocols and interpreted cautiously, sEMG can yield reliable, meaningful This thesis adheres to the principles of the Declaration of Helsinki (157) insights into neuromuscular function, particularly for evaluating muscle and the European Code of Conduct for Research Integrity (158), upholding activation patterns and fatigue. reliability, honesty, respect, and accountability throughout the entire research process. Similarly, the reliability of MOCAP has been assessed extensively. A primary limitation arises from soft tissue artefacts caused by muscle The positive outcomes of all four studies were considered to outweigh contraction, gravity, skin deformation, or sliding of markers attached to any potential discomfort experienced by the study participants. Given the skin (153). Concurrent validity is highest in the sagittal plane (correlation that the methodologies employed were non-invasive, the burden placed coefficient >0.7), lower in the coronal plane (0.5-0.6), and lowest in the on participants can be considered minimal. transverse plane (≤0.4), (154). Validation studies often compare MOCAP with radiostereometric analysis (RSA), in which tantalum markers are Biomechanical data collection often requires participants to wear less implanted into cortical bone and tracked by stereoradiographs (154, 155). clothing (e.g., shorts and a top), which may be perceived as somewhat The strongest correlations between these measurement modalities uncomfortable or awkward by some individuals. The data collection have been reported for hip flexion and abduction, while rotational process can be time-consuming, as sEMG electrode placement measures show poorer agreement (155). requires thorough skin preparation, which may occasionally cause minor skin irritation. No participants reported complaints, and no dropouts Fändriks et al. compared three marker sets against RSA for knee motion occurred due to personal issues related to the method during the analysis (156). Although sagittal-plane flexion–extension measures were laboratory investigations. Also, the isometric contractions performed consistent across all sets, each underestimated true skeletal motion. during the sEMG session can cause some muscle soreness during one Frontal and transverse plane measures were highly inconsistent, 108 DISCUSSION KARI HUSETH 109 or two days after the testing session. All participants were fully informed of these procedures beforehand, and informed consent was always obtained. The studies involved sensitive personal data related to health and well-being; however, all data were pseudo-anonymized, and the coding key was securely stored and accessible only to the responsible researcher. STATISTICAL CONSIDERATIONS The four studies applied statistical methods selected not only for their suitability to each aim but also for their capacity to probe the biomechanical chain from multiple angles. Studies I–II used frequentist tests for controlled EMG comparisons; Study III employed Bayesian hierarchical modelling to capture limb-to-limb asymmetries and quantify uncertainty in gait after an Achilles tendon rupture; and Study IV applied statistical parametric mapping to reveal time-specific differences in continuous kinetic and EMG profiles. This methodological diversity reflects the exploratory incentive of the thesis; a deliberate effort to apply statistical tools capable of uncovering both broad group-level patterns and more subtle, individualized adaptations. By integrating frequentist, Bayesian, and time-series approaches, the work achieved a multifaceted perspective on neuromechanical function, enabling a richer and more precise exploration of how mechanical and neural influences interact along the biomechanical chain. GENDER CONSIDERATION Participant sex was recorded; however, the limited number of participants precluded meaningful subgroup analyses, which were also beyond the scope of the present studies. Although sex-related aspects of Achilles tendon rupture have been explored (159-161), they warrant more focused attention in future research. 110 DISCUSSION KARI HUSETH 111 or two days after the testing session. All participants were fully informed of these procedures beforehand, and informed consent was always obtained. The studies involved sensitive personal data related to health and well-being; however, all data were pseudo-anonymized, and the coding key was securely stored and accessible only to the responsible researcher. STATISTICAL CONSIDERATIONS The four studies applied statistical methods selected not only for their suitability to each aim but also for their capacity to probe the biomechanical chain from multiple angles. Studies I–II used frequentist tests for controlled EMG comparisons; Study III employed Bayesian hierarchical modelling to capture limb-to-limb asymmetries and quantify uncertainty in gait after an Achilles tendon rupture; and Study IV applied statistical parametric mapping to reveal time-specific differences in continuous kinetic and EMG profiles. This methodological diversity reflects the exploratory incentive of the thesis; a deliberate effort to apply statistical tools capable of uncovering both broad group-level patterns and more subtle, individualized adaptations. By integrating frequentist, Bayesian, and time-series approaches, the work achieved a multifaceted perspective on neuromechanical function, enabling a richer and more precise exploration of how mechanical and neural influences interact along the biomechanical chain. GENDER CONSIDERATION Participant sex was recorded; however, the limited number of participants precluded meaningful subgroup analyses, which were also beyond the scope of the present studies. Although sex-related aspects of Achilles tendon rupture have been explored (159-161), they warrant more focused attention in future research. 110 DISCUSSION KARI HUSETH 111 9. Strengths and limitations STRENGTHS A major strength of this thesis lies in its  comprehensive investigation of the biomechanical chain from the foot to the trunk, integrating EMG, kinematic, and kinetic data across multiple functional tasks. This multilevel approach offers novel insight into both methodological and clinical aspects of segmental coordination during human movement. First, the inclusion of  two methodological studies (Studies I and II)  served to strengthen the overall methodological framework by addressing critical aspects of EMG normalization and foot positioning. The standardized test protocols, including consistent MVIC procedures and electrode placements based on established anatomical landmarks, enhanced the reliability and reproducibility of the EMG data used in the subsequent ATR-related investigations. Second, the application of ecologically valid motor tasks, such as stair climbing, walking, and jogging, increases the translational relevance of the findings. The inclusion of different foot positions and gait speeds allowed for a nuanced exploration of how neuromechanical strategies may vary under changing mechanical demands, meaning variations in external loading and movement constraints imposed by speed and foot alignment. Third, the use of  advanced motion capture technologies, including a high-resolution optical tracking system synchronized with force plates, enabled precise analysis of joint kinetics and support moments using inverse dynamics. These biomechanical tools allowed for time- continuous, segment-specific analyses that are rarely integrated in Every morning in Africa, a gazelle wakes up, it knows it must clinical gait research, particularly in relation to ATR. outrun the fastest lion or it will be killed. Every morning in Afri- ca, a lion wakes up. It knows it must run faster than the slowest Finally,  Studies III and IV represent an effort to explore locomotor gazelle, or it will starve. It doesn’t matter whether you’re the lion adaptations after an ATR, beyond the ankle, providing detailed or a gazelle-when the sun comes up, you’d better be running. descriptions of interlimb differences in muscle activation, ROM and support strategies during walking and running. The integration of 👥👥 CHRISTOPHER MCDOUGALL 112 STRENGTHS AND LIMITATIONS KARI HUSETH 113 9. Strengths and limitations STRENGTHS A major strength of this thesis lies in its  comprehensive investigation of the biomechanical chain from the foot to the trunk, integrating EMG, kinematic, and kinetic data across multiple functional tasks. This multilevel approach offers novel insight into both methodological and clinical aspects of segmental coordination during human movement. First, the inclusion of  two methodological studies (Studies I and II)  served to strengthen the overall methodological framework by addressing critical aspects of EMG normalization and foot positioning. The standardized test protocols, including consistent MVIC procedures and electrode placements based on established anatomical landmarks, enhanced the reliability and reproducibility of the EMG data used in the subsequent ATR-related investigations. Second, the application of ecologically valid motor tasks, such as stair climbing, walking, and jogging, increases the translational relevance of the findings. The inclusion of different foot positions and gait speeds allowed for a nuanced exploration of how neuromechanical strategies may vary under changing mechanical demands, meaning variations in external loading and movement constraints imposed by speed and foot alignment. Third, the use of  advanced motion capture technologies, including a high-resolution optical tracking system synchronized with force plates, enabled precise analysis of joint kinetics and support moments using inverse dynamics. These biomechanical tools allowed for time- continuous, segment-specific analyses that are rarely integrated in Every morning in Africa, a gazelle wakes up, it knows it must clinical gait research, particularly in relation to ATR. outrun the fastest lion or it will be killed. Every morning in Afri- ca, a lion wakes up. It knows it must run faster than the slowest Finally,  Studies III and IV represent an effort to explore locomotor gazelle, or it will starve. It doesn’t matter whether you’re the lion adaptations after an ATR, beyond the ankle, providing detailed or a gazelle-when the sun comes up, you’d better be running. descriptions of interlimb differences in muscle activation, ROM and support strategies during walking and running. The integration of 👥👥 CHRISTOPHER MCDOUGALL 112 STRENGTHS AND LIMITATIONS KARI HUSETH 113 EMG, joint kinetics, and kinematics support a deep understanding of were discussed conceptually but not measured, representing an segmental compensation patterns in this clinical population. important avenue for future research with a biopsychosocial approach. Finally, biomechanical tools quantify parameters such as muscle LIMITATIONS activation, joint angles, and forces with high precision, but offer only a Despite its strengths, this work has several limitations. The sample sizes, partial view of functional capacity. Laboratory measurements cannot typical for the gait EMG studies, were large enough for within-subject fully capture the complexity, variability, and adaptability of movements in analyses but limit generalizability, particularly in terms of inter-individual natural environments. Thus, it is suggested that biomechanical analysis variability. In Study IV, the inclusion of both surgically and non-surgically should be interpreted as part of a broader framework integrating treated ATR participants introduced clinical heterogeneity that was not ecological, psychological, and functional perspectives. stratified in the analysis. The cross-sectional design of Studies III and IV precludes conclusions about the temporal progression of compensatory strategies following ATR. Longitudinal data are needed to determine whether observed adaptations persist, resolve, or evolve over time. Laboratory-based tasks, while controlled, may not fully reflect sport- specific or real-world movement demands. Foot posture manipulations in Study II, for example, although allowing individual adaptation, may not completely replicate natural pronation or supination of the foot. Methodologically, surface EMG, though widely accepted, remains vulnerable to signal attenuation, cross-talk, and skin movement artifacts, particularly for deep or small muscles. Likewise, skin-mounted optical markers, despite high spatial resolution, can be affected by soft tissue artifacts, especially in the frontal and transverse planes, which may reduce the precision of joint angle estimates. Although task execution was standardized with instructions and practice trials, individual movement strategies may still have influenced outcomes. Awareness of instrumentation (e.g., electrodes, markers) may also – at least slightly – have altered performance. Psychological factors such as fear of reinjury or reduced confidence 114 STRENGTHS AND LIMITATIONS KARI HUSETH 115 EMG, joint kinetics, and kinematics support a deep understanding of were discussed conceptually but not measured, representing an segmental compensation patterns in this clinical population. important avenue for future research with a biopsychosocial approach. Finally, biomechanical tools quantify parameters such as muscle LIMITATIONS activation, joint angles, and forces with high precision, but offer only a Despite its strengths, this work has several limitations. The sample sizes, partial view of functional capacity. Laboratory measurements cannot typical for the gait EMG studies, were large enough for within-subject fully capture the complexity, variability, and adaptability of movements in analyses but limit generalizability, particularly in terms of inter-individual natural environments. Thus, it is suggested that biomechanical analysis variability. In Study IV, the inclusion of both surgically and non-surgically should be interpreted as part of a broader framework integrating treated ATR participants introduced clinical heterogeneity that was not ecological, psychological, and functional perspectives. stratified in the analysis. The cross-sectional design of Studies III and IV precludes conclusions about the temporal progression of compensatory strategies following ATR. Longitudinal data are needed to determine whether observed adaptations persist, resolve, or evolve over time. Laboratory-based tasks, while controlled, may not fully reflect sport- specific or real-world movement demands. Foot posture manipulations in Study II, for example, although allowing individual adaptation, may not completely replicate natural pronation or supination of the foot. Methodologically, surface EMG, though widely accepted, remains vulnerable to signal attenuation, cross-talk, and skin movement artifacts, particularly for deep or small muscles. Likewise, skin-mounted optical markers, despite high spatial resolution, can be affected by soft tissue artifacts, especially in the frontal and transverse planes, which may reduce the precision of joint angle estimates. Although task execution was standardized with instructions and practice trials, individual movement strategies may still have influenced outcomes. Awareness of instrumentation (e.g., electrodes, markers) may also – at least slightly – have altered performance. Psychological factors such as fear of reinjury or reduced confidence 114 STRENGTHS AND LIMITATIONS KARI HUSETH 115 10. Conclusion From the integrated findings of the present thesis, several overarching insights emerge. The obtained data contribute to improve our understanding of how the biomechanical chain operates in both healthy and post-injury contexts, and they may provide a potential framework for both future research strategies and possibly improved understanding of given rehabilitation strategies: • Distal changes dominate but may propagate proximally Neuromechanical effects are strongest locally and in adjacent segments, with attenuation observed more proximally; their impact depends on task demands, individual variability, and compensatory capacity. • Neuromuscular variability is intrinsic and functional  High within- and between-individual variability reflects motor abundance, allowing exploration of alternative coordination strategies to maintain performance despite constraints. • Adaptations are context- and phase-specific  Distal–to-proximal effects are more evident in walking than running, shaped by stance duration, push-off demands, and the elastic energy use of the Achilles tendon. • Adaptive compensations after an ATR remain localized  Even one year post-injury, kinetic and EMG asymmetries are most apparent distally, with no consistent changes at the hip or trunk, suggesting that rehabilitation may be particularly relevant at the local level. • The biomechanical chain is dynamic, not rigid  One of the wonderful aspects of running is that there is no definition of a ‘runner’ that you must live up to. 👥👥 KARA GOUCHER 116 CONCLUSION KARI HUSETH 117 10. Conclusion From the integrated findings of the present thesis, several overarching insights emerge. The obtained data contribute to improve our understanding of how the biomechanical chain operates in both healthy and post-injury contexts, and they may provide a potential framework for both future research strategies and possibly improved understanding of given rehabilitation strategies: • Distal changes dominate but may propagate proximally Neuromechanical effects are strongest locally and in adjacent segments, with attenuation observed more proximally; their impact depends on task demands, individual variability, and compensatory capacity. • Neuromuscular variability is intrinsic and functional  High within- and between-individual variability reflects motor abundance, allowing exploration of alternative coordination strategies to maintain performance despite constraints. • Adaptations are context- and phase-specific  Distal–to-proximal effects are more evident in walking than running, shaped by stance duration, push-off demands, and the elastic energy use of the Achilles tendon. • Adaptive compensations after an ATR remain localized  Even one year post-injury, kinetic and EMG asymmetries are most apparent distally, with no consistent changes at the hip or trunk, suggesting that rehabilitation may be particularly relevant at the local level. • The biomechanical chain is dynamic, not rigid  One of the wonderful aspects of running is that there is no definition of a ‘runner’ that you must live up to. 👥👥 KARA GOUCHER 116 CONCLUSION KARI HUSETH 117 11. Clinical implication It is well established that rehabilitation is grounded in clinical reasoning, emphasizing individualized, task-specific loading, functional progression, and continuous outcome assessment guided by the specific and individualized patient goals (161-165).The clinical implications of this thesis build on this foundation and further, the aim to promote an even more individualized rehabilitation approach and potentially providing new insights for practice. As with all tendon repair, healing is a slow process, and this needs to be carefully respected when building a suitable and resilient tendon (166). In harmony with previously suggested rehabilitation progression in terms of an ATR (62, 72), post-injury rehabilitation is likely to benefit from being even more individually tailored, progressively loaded, and finally task-specific. The focus might therefore not only be related to restoring plantar flexor strength, but also on enhancing neuromuscular coordination, tendon stiffness, and resilience across the entire kinetic chain. Guided by the  proposed Absorptive Coupling Model, this process may recognize that mechanical effects of an Achilles tendon rupture are strongest locally and in adjacent segments, while they attenuate more proximally, with neural control maintaining overall coordination. Consequently, and in harmony with this model, the rehabilitation program would therefore need to address local tendon capacity and Han kunde tydligt se Snusmumrikens fotspår i den våta jorden. adjacent segment reconditioning, while ensuring effective reintegration De fnattade hit och dit och var ganska svåra att följa. Ibland of proximal structures for an efficient whole-chain function. gjorde de långa skutt och korsade sig själva. Han har varit glad, funderade Mumintrollet. Här har han gjort en kullerbytta, det är While structured programs provide valuable guidance, rehabilitation may klart och tydligt. also be enhanced by viewing it as a dynamic capacity-building process, He could see Snufkin’s footprints clearly in the damp earth. They with attentiveness to when individual deviations from the structure zigzagged this way and that, tricky to follow. Now and then they may become necessary. Loading can be systematically and gradually leapt far, sometimes even crossing themselves. He’s been in high progressed with the goal to stimulate collagen remodeling, optimize spirits, thought Moomintroll. Here he’s turned a somersault, no doubt about it. stiffness, and refine intersegmental coordination. This progression might then be  individually calibrated  according to the tendon healing 👥👥 TOVE JANSSON stage, structural integrity, neuromuscular control, and psychological 118 CLINICAL IMPLICATION KARI HUSETH 119 11. Clinical implication It is well established that rehabilitation is grounded in clinical reasoning, emphasizing individualized, task-specific loading, functional progression, and continuous outcome assessment guided by the specific and individualized patient goals (161-165).The clinical implications of this thesis build on this foundation and further, the aim to promote an even more individualized rehabilitation approach and potentially providing new insights for practice. As with all tendon repair, healing is a slow process, and this needs to be carefully respected when building a suitable and resilient tendon (166). In harmony with previously suggested rehabilitation progression in terms of an ATR (62, 72), post-injury rehabilitation is likely to benefit from being even more individually tailored, progressively loaded, and finally task-specific. The focus might therefore not only be related to restoring plantar flexor strength, but also on enhancing neuromuscular coordination, tendon stiffness, and resilience across the entire kinetic chain. Guided by the  proposed Absorptive Coupling Model, this process may recognize that mechanical effects of an Achilles tendon rupture are strongest locally and in adjacent segments, while they attenuate more proximally, with neural control maintaining overall coordination. Consequently, and in harmony with this model, the rehabilitation program would therefore need to address local tendon capacity and Han kunde tydligt se Snusmumrikens fotspår i den våta jorden. adjacent segment reconditioning, while ensuring effective reintegration De fnattade hit och dit och var ganska svåra att följa. Ibland of proximal structures for an efficient whole-chain function. gjorde de långa skutt och korsade sig själva. Han har varit glad, funderade Mumintrollet. Här har han gjort en kullerbytta, det är While structured programs provide valuable guidance, rehabilitation may klart och tydligt. also be enhanced by viewing it as a dynamic capacity-building process, He could see Snufkin’s footprints clearly in the damp earth. They with attentiveness to when individual deviations from the structure zigzagged this way and that, tricky to follow. Now and then they may become necessary. Loading can be systematically and gradually leapt far, sometimes even crossing themselves. He’s been in high progressed with the goal to stimulate collagen remodeling, optimize spirits, thought Moomintroll. Here he’s turned a somersault, no doubt about it. stiffness, and refine intersegmental coordination. This progression might then be  individually calibrated  according to the tendon healing 👥👥 TOVE JANSSON stage, structural integrity, neuromuscular control, and psychological 118 CLINICAL IMPLICATION KARI HUSETH 119 readiness. Variability in load magnitude, direction, and task-specific context will challenge both mechanical and neural systems, enhancing adaptability and resilience to the often unpredictable real-world demands. Based on the findings of the present thesis, together with previously established principles, the following are suggested as potential guiding principles. • Individually-tailored rehabilitation protocols: adjust the protocol- by taking into account the biological healing process to each patient’s biomechanics, goals, and recovery rate. • Progressive load: gradually increase the demands to promote tendon adaptation and structural resilience. • Task-specific  interventions: Use functional, context-rich activi- ties for daily life and sports activity. • Integrated kinetic chain focus: target plantar flexor strength, neuromuscular coordination, and multi-segment reintegration. • Normalized movement to the individual: guide toward efficient and sustainable strategies while respecting individual variability. • Shape motor variability: encourage adaptive flexibility, avoid maladaptive patterns. • Continuously adjustable: modify the response according to the evolving structural and coordination capacity. In terms of this integrated approach, successful rehabilitation may not be defined solely by restoring the symmetry or baseline gait, but by developing a  resilient and dynamic tendon–muscle–neural system  capable of sustaining high performance and adapting to the individually varying demands of sport, work, and daily life. 120 CLINICAL IMPLICATION KARI HUSETH 121 readiness. Variability in load magnitude, direction, and task-specific context will challenge both mechanical and neural systems, enhancing adaptability and resilience to the often unpredictable real-world demands. Based on the findings of the present thesis, together with previously established principles, the following are suggested as potential guiding principles. • Individually-tailored rehabilitation protocols: adjust the protocol- by taking into account the biological healing process to each patient’s biomechanics, goals, and recovery rate. • Progressive load: gradually increase the demands to promote tendon adaptation and structural resilience. • Task-specific  interventions: Use functional, context-rich activi- ties for daily life and sports activity. • Integrated kinetic chain focus: target plantar flexor strength, neuromuscular coordination, and multi-segment reintegration. • Normalized movement to the individual: guide toward efficient and sustainable strategies while respecting individual variability. • Shape motor variability: encourage adaptive flexibility, avoid maladaptive patterns. • Continuously adjustable: modify the response according to the evolving structural and coordination capacity. In terms of this integrated approach, successful rehabilitation may not be defined solely by restoring the symmetry or baseline gait, but by developing a  resilient and dynamic tendon–muscle–neural system  capable of sustaining high performance and adapting to the individually varying demands of sport, work, and daily life. 120 CLINICAL IMPLICATION KARI HUSETH 121 12. Future perspectives The findings of this thesis highlight several avenues for future investigation spanning methodological, experimental, and applied domains. Addressing these domains will deepen the understanding of the biomechanical chain and improve clinical outcomes for individuals with distal impairments such as an ATR. LONGITUDINAL TRACKING OF RECOVERY TRAJECTORIES Future studies are suggested to be able to follow ATR recovery from the acute phase through long-term outcomes, mapping changes in joint kinetics, kinematics, and EMG patterns. Such tracking would help identify critical intervention windows and determine whether observed compensations resolve, persist, or develop into maladaptive strategies that affect efficiency, load distribution, or secondary joint health. INTEGRATION OF PSYCHOLOGICAL FACTORS WITH BIOMECHANICS Fear of re-injury, reduced limb confidence, and perceived instability may likely shape post-ATR movement strategies. Combining validated psychological assessments (e.g., kinesiophobia scales) with biomechanical, EMG measures and functional scores could improve predictive models of adaptation. A biopsychosocial approach would support interventions that address both mechanical deficits and movement confidence. DYNAMIC EVALUATION OF ORTHOSES AND FOOTWEAR Many orthoses and footwear products claim to influence the kinetic chain beyond the foot, yet evidence under dynamic, real-world Most runners hope running will always be a part of their lives. conditions is scarce. Building on the present thesis, future research I’ll be happy if running and I can grow old together. efforts should implement and evaluate these intervention strategies 👥👥 HARUKI MURAKAMI in walking, running, and sport-specific tasks, quantifying local and 122 FUTURE PERSPECTIVES KARI HUSETH 123 12. Future perspectives The findings of this thesis highlight several avenues for future investigation spanning methodological, experimental, and applied domains. Addressing these domains will deepen the understanding of the biomechanical chain and improve clinical outcomes for individuals with distal impairments such as an ATR. LONGITUDINAL TRACKING OF RECOVERY TRAJECTORIES Future studies are suggested to be able to follow ATR recovery from the acute phase through long-term outcomes, mapping changes in joint kinetics, kinematics, and EMG patterns. Such tracking would help identify critical intervention windows and determine whether observed compensations resolve, persist, or develop into maladaptive strategies that affect efficiency, load distribution, or secondary joint health. INTEGRATION OF PSYCHOLOGICAL FACTORS WITH BIOMECHANICS Fear of re-injury, reduced limb confidence, and perceived instability may likely shape post-ATR movement strategies. Combining validated psychological assessments (e.g., kinesiophobia scales) with biomechanical, EMG measures and functional scores could improve predictive models of adaptation. A biopsychosocial approach would support interventions that address both mechanical deficits and movement confidence. DYNAMIC EVALUATION OF ORTHOSES AND FOOTWEAR Many orthoses and footwear products claim to influence the kinetic chain beyond the foot, yet evidence under dynamic, real-world Most runners hope running will always be a part of their lives. conditions is scarce. Building on the present thesis, future research I’ll be happy if running and I can grow old together. efforts should implement and evaluate these intervention strategies 👥👥 HARUKI MURAKAMI in walking, running, and sport-specific tasks, quantifying local and 122 FUTURE PERSPECTIVES KARI HUSETH 123 proximal adaptations and their impact on propulsion, stability, and load management. PERTURBATION-BASED ASSESSMENTS OF CHAIN ROBUSTNESS Steady-state gait may mask distal–proximal coupling. Introducing controlled perturbations such as surface changes, unexpected loads, or directional shifts could reveal latent mechanical and neural linkages. Such testing could identify individuals with reduced adaptability, who may be at higher risk of reinjury. DEVELOPMENT OF UPDATED NORMATIVE DATASETS Current gait and EMG reference datasets are often outdated or based on small, homogeneous samples. Thus, there is a need for establishing diverse normative datasets that include joint power, muscle activation, and variability metrics across walking, running, and other functional tasks to improve benchmarking and interpretation for post-injury assessments. 124 FUTURE PERSPECTIVES KARI HUSETH 125 proximal adaptations and their impact on propulsion, stability, and load management. PERTURBATION-BASED ASSESSMENTS OF CHAIN ROBUSTNESS Steady-state gait may mask distal–proximal coupling. Introducing controlled perturbations such as surface changes, unexpected loads, or directional shifts could reveal latent mechanical and neural linkages. Such testing could identify individuals with reduced adaptability, who may be at higher risk of reinjury. DEVELOPMENT OF UPDATED NORMATIVE DATASETS Current gait and EMG reference datasets are often outdated or based on small, homogeneous samples. Thus, there is a need for establishing diverse normative datasets that include joint power, muscle activation, and variability metrics across walking, running, and other functional tasks to improve benchmarking and interpretation for post-injury assessments. 124 FUTURE PERSPECTIVES KARI HUSETH 125 13. Acknowledgement This thesis has been a shared adventure. Many people contributed along the way. First and foremost, a heartfelt thank you to all the study participants. Your endless patience was exceptional. Your participation made this work possible. Annelie Gutke, my main supervisor. You stepped in during a time of great change. Your unwavering commitment and willingness to take on this role when life looked very different mean more to me than words can express-We shall not cease from exploration*! Your steady guidance, exceptional support, and keen eye for detail have anchored me throughout this journey. Your ability to return to the essentials, with clarity, logic, and care, has been a true source of strength. Your deep dedication to physical therapy, clinical methodology, and meaningful outcomes is truly inspiring. I am deeply and sincerely grateful for all you have contributed. I could not have come this far without you. Jón Karlsson, my co-supervisor. Your remarkable availability and rapid, thoughtful feedback, despite everything else on your agenda, have been truly extraordinary. Your constant encouragement and genuine kindness have most definitely propelled this thesis forward. Your ability to pinpoint what is essential, combined with your vast expertise in orthopedic research, has been an invaluable guide throughout this journey. Roy Tranberg, my co-supervisor. We’ve journeyed together through both joy and challenge as life unfolded around us for quite some time. Your commitment to biomechanics, gait analysis, and scientific inquiry has been instrumental throughout. From clinical application to methodological refinement, your expertise has shaped both the Nog finns det mål och mening i vår färd— content and direction of this work. With steady reminders to “not men det är vägen, som är mödan värd. overcomplicate it,” you’ve shown remarkable patience-with cryptic key commands, puzzling Excel sheets, mysterious EndNote libraries, Indeed, there may be aim and goal to our stride— and the quirks of Mac. Your deep respect for the gait laboratory, and but it is the road that makes the effort abide. for what our tools and analyses represent, has been a lasting source of 👥👥 KARIN BOYE guidance and inspiration. 126 ACKNOWLEDGEMENT KARI HUSETH 127 13. Acknowledgement This thesis has been a shared adventure. Many people contributed along the way. First and foremost, a heartfelt thank you to all the study participants. Your endless patience was exceptional. Your participation made this work possible. Annelie Gutke, my main supervisor. You stepped in during a time of great change. Your unwavering commitment and willingness to take on this role when life looked very different mean more to me than words can express-We shall not cease from exploration*! Your steady guidance, exceptional support, and keen eye for detail have anchored me throughout this journey. Your ability to return to the essentials, with clarity, logic, and care, has been a true source of strength. Your deep dedication to physical therapy, clinical methodology, and meaningful outcomes is truly inspiring. I am deeply and sincerely grateful for all you have contributed. I could not have come this far without you. Jón Karlsson, my co-supervisor. Your remarkable availability and rapid, thoughtful feedback, despite everything else on your agenda, have been truly extraordinary. Your constant encouragement and genuine kindness have most definitely propelled this thesis forward. Your ability to pinpoint what is essential, combined with your vast expertise in orthopedic research, has been an invaluable guide throughout this journey. Roy Tranberg, my co-supervisor. We’ve journeyed together through both joy and challenge as life unfolded around us for quite some time. Your commitment to biomechanics, gait analysis, and scientific inquiry has been instrumental throughout. From clinical application to methodological refinement, your expertise has shaped both the Nog finns det mål och mening i vår färd— content and direction of this work. With steady reminders to “not men det är vägen, som är mödan värd. overcomplicate it,” you’ve shown remarkable patience-with cryptic key commands, puzzling Excel sheets, mysterious EndNote libraries, Indeed, there may be aim and goal to our stride— and the quirks of Mac. Your deep respect for the gait laboratory, and but it is the road that makes the effort abide. for what our tools and analyses represent, has been a lasting source of 👥👥 KARIN BOYE guidance and inspiration. 126 ACKNOWLEDGEMENT KARI HUSETH 127 Per Aagaard, my co-supervisor. I dare say-nothing gets past you! Your Katarina Helander Nilsson and Elin Larsson, co-writers Studies III eye for details is truly remarkable. Your deep knowledge of biomechanics and IV. Thank you for including me in your research group and giving and research-and the generosity with which you’ve shared it-have had me the opportunity to apply my work to a clinically relevant cohort. I’m a tremendous impact on me. I’ve learned so much from you, particularly especially grateful for your initial support with study design and your in understanding EMG processing and its implications. Our supervisor contribution to collecting and integrating the PROMs. Your involvement meetings at café tables, laptops open in Copenhagen, remain especially made a significant difference. memorable and speak volumes about your humility, accessibility, and refreshing straight-forwardness. The road taken** would not have been Lotta Falkheden Henning, physical therapist. Thank you for your walked without you. invaluable assistance in recruiting participants from the ongoing DUSTAR project for study III and IV-without your efforts, there simply Roland Zûgner, my co-supervisor. I will remember you with deep joy would have been no cohort. And thank you for your collaboration, in my heart. I truly miss our whiteboard discussions, the reflections especially as we juggled the ever-faithful Bagheera Omega shoes that on clinical reasoning in physical therapy, and the way we explored the have stood the test of time in the lab. practical application of our biomechanical research. Somehow, you always found the time. I miss the laughter, your unwavering curiosity and Ulla Tang and Jacqueline Siegenthaler, orthopedic engineers. What dedication, and that unmistakable dry Gothenburg humor. This one is laughs we’ve shared over the marvelous MVIC apparatus! Working side for you: Normal is an illusion. What is normal for the spider is chaos for by side with you has been such fun. Your curiosity for feet, your genuinely the fly*** . Thank you-for everything. Your legacy will live on. grounded passion for people and for what truly matters in life, not to mention your professional enthusiasm, is an outstanding combination. Guðni Rafn Hardarson, fellow PhD-student and dear Icelandic lab partner and co-writer for Studies III and IV. Our days in the gait lab, To my colleagues at the Orthopedic Research Unit at Gröna stråket meticulously applying markers and sensors, performing MVICs- and and R huset. Where conversations can jump from p-values to food those never-ending adjustments along the way -even so, it’s been fun. recipes in the blink of an eye. It has been a privilege to share both the The work you put into the analysis, V3D, MATLAB, and SPM for these depths of sorrow and the heights of happiness with such a dynamic and studies has been extensive and thorough, carried out with care and warm group. A huge thanks for all the support, encouragement, and dedication that I truly appreciate. You are truly the most helpful person I laughs along the way! know. When the road got a bit rough, you were a rock, solid, steady, and Karin Larsson and Eva Runesson, research colleagues. At the old always there. Your insight and knowledge of the scientific world are vast, Lundberg’s lab, Gröna stråket, you were so welcoming and supportive. I and I have no doubt: I see a rising star! am truly grateful for your insight and enthusiasm, which gave me a solid Annelie Brorsson, co-writer Studies III and IV. It’s always a pleasure to foundation, and for our ‘science kitchen’ talks that set me on the right drop by your office-sometimes for a bit of lighthearted nonsense, but path. more often to get your clear, thoughtful answers to scientific questions, Lars Ekström, colleague at the Orthopedic Research Unit. Thank especially about the Achilles tendon. Your laughter echoes down the you for your valuable input and insightful discussions. Your clear hallway, carrying me a little closer to the finish line. 128 ACKNOWLEDGEMENT KARI HUSETH 129 Per Aagaard, my co-supervisor. I dare say-nothing gets past you! Your Katarina Helander Nilsson and Elin Larsson, co-writers Studies III eye for details is truly remarkable. Your deep knowledge of biomechanics and IV. Thank you for including me in your research group and giving and research-and the generosity with which you’ve shared it-have had me the opportunity to apply my work to a clinically relevant cohort. I’m a tremendous impact on me. I’ve learned so much from you, particularly especially grateful for your initial support with study design and your in understanding EMG processing and its implications. Our supervisor contribution to collecting and integrating the PROMs. Your involvement meetings at café tables, laptops open in Copenhagen, remain especially made a significant difference. memorable and speak volumes about your humility, accessibility, and refreshing straight-forwardness. The road taken** would not have been Lotta Falkheden Henning, physical therapist. Thank you for your walked without you. invaluable assistance in recruiting participants from the ongoing DUSTAR project for study III and IV-without your efforts, there simply Roland Zûgner, my co-supervisor. I will remember you with deep joy would have been no cohort. And thank you for your collaboration, in my heart. I truly miss our whiteboard discussions, the reflections especially as we juggled the ever-faithful Bagheera Omega shoes that on clinical reasoning in physical therapy, and the way we explored the have stood the test of time in the lab. practical application of our biomechanical research. Somehow, you always found the time. I miss the laughter, your unwavering curiosity and Ulla Tang and Jacqueline Siegenthaler, orthopedic engineers. What dedication, and that unmistakable dry Gothenburg humor. This one is laughs we’ve shared over the marvelous MVIC apparatus! Working side for you: Normal is an illusion. What is normal for the spider is chaos for by side with you has been such fun. Your curiosity for feet, your genuinely the fly*** . Thank you-for everything. Your legacy will live on. grounded passion for people and for what truly matters in life, not to mention your professional enthusiasm, is an outstanding combination. Guðni Rafn Hardarson, fellow PhD-student and dear Icelandic lab partner and co-writer for Studies III and IV. Our days in the gait lab, To my colleagues at the Orthopedic Research Unit at Gröna stråket meticulously applying markers and sensors, performing MVICs- and and R huset. Where conversations can jump from p-values to food those never-ending adjustments along the way -even so, it’s been fun. recipes in the blink of an eye. It has been a privilege to share both the The work you put into the analysis, V3D, MATLAB, and SPM for these depths of sorrow and the heights of happiness with such a dynamic and studies has been extensive and thorough, carried out with care and warm group. A huge thanks for all the support, encouragement, and dedication that I truly appreciate. You are truly the most helpful person I laughs along the way! know. When the road got a bit rough, you were a rock, solid, steady, and Karin Larsson and Eva Runesson, research colleagues. At the old always there. Your insight and knowledge of the scientific world are vast, Lundberg’s lab, Gröna stråket, you were so welcoming and supportive. I and I have no doubt: I see a rising star! am truly grateful for your insight and enthusiasm, which gave me a solid Annelie Brorsson, co-writer Studies III and IV. It’s always a pleasure to foundation, and for our ‘science kitchen’ talks that set me on the right drop by your office-sometimes for a bit of lighthearted nonsense, but path. more often to get your clear, thoughtful answers to scientific questions, Lars Ekström, colleague at the Orthopedic Research Unit. Thank especially about the Achilles tendon. Your laughter echoes down the you for your valuable input and insightful discussions. Your clear hallway, carrying me a little closer to the finish line. 128 ACKNOWLEDGEMENT KARI HUSETH 129 perspective, deep knowledge, and willingness to share have been Emelie Ahlstedt, administrator at the Orthopedic Research Unit. Thank invaluable. And thank you for being such a good sport in conceptualizing you for keeping the unit so well organized and for always being quick to the gait laboratory. answer questions with kindness and support. Inge Ringdal, physical therapist and Norwegian colleague. I am more Pontus Andersson, professional illustrator. Thank you for the outstand- than thankful for welcoming me into EMG discussions, for the time and ing illustrations and your patience through countless adjustments. Your encouragement you gave me at Staven Kysthospital, and for kindly ability to translate complex ideas into clear, compelling visuals has checking the Norwegian summary of this thesis. greatly enriched this thesis. Michael Miller, my mentor at University of Lund. You were there when Guðni Olafsson, graphic designer. I am so grateful for your work on the it started, the exploration of feet, trunk, and EMG, your encouragement, splendid layout of this thesis. Your sense of detail and design has made insight, and structure provided me with direction. Warm thanks also to it not only professional but also genuinely pleasing to the eye, turning you and Ann for your hospitality in Löberöd during my years in Lund. the text into a book that I am proud to present. Helena Brisby, former head of the Department of Orthopedics at the Koen Simons, statistician . You lured me into the world of Bayesian Institute of Clinical Sciences, Sahlgrenska Academy, University of statistics, something I was initially wary of but now truly grateful for. Gothenburg. Thank you for accepting my thesis proposal. I so appreciate all the effort you put into Study III, and your endless patience and wonderfully pedagogical way of guiding me through my Ola Rolfson, current head of the Department of Orthopedics at the many questions. Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg for granting me the opportunity to pursue my doctoral Fysio Forum, my workplace-a small physical therapy clinic with space studies within the Institute of Clinical Sciences. for the individual and time to care. Daily encounters with patients have grounded me in the realities of clinical practice while providing the Pernilla Eliasson, head of the Orthopedic Research Unit at the inspiration and support to pursue my academic journey. In the balance Department of Orthopedics, Sahlgrenska University Hospital. Thank between hands-on care and scientific curiosity, my work has found its you for making space for this research to happen and for your generous purpose. support in seeing it through. Anna Kimming, friend and fellow physical therapist. From the feet Linda Johansson, Cina Holmer, Anna Orosz and Maya Daneva, upward, your perspective has always been grounded, insightful, and administrators at the Institute of Clinical Sciences Sahlgrenska human. Thank you for your unwavering support, your keen interest, Academy, University of Gothenburg. Thank you for your invaluable and your deep-rooted commitment to the wellbeing of others. From guidance in navigating the winding administrative landscape behind the hands-on treatment to clinical reasoning and sharp observation, your academic requirements of this thesis, and for keeping me well on track enthusiasm and endurance have been a constant source of inspiration. throughout the process. We walked side by side through OMT 3 and the Master’s program in Lund-you always a step ahead, always generous with your notes and assignments. I’m deeply grateful for your companionship on this journey. 130 ACKNOWLEDGEMENT KARI HUSETH 131 perspective, deep knowledge, and willingness to share have been Emelie Ahlstedt, administrator at the Orthopedic Research Unit. Thank invaluable. And thank you for being such a good sport in conceptualizing you for keeping the unit so well organized and for always being quick to the gait laboratory. answer questions with kindness and support. Inge Ringdal, physical therapist and Norwegian colleague. I am more Pontus Andersson, professional illustrator. Thank you for the outstand- than thankful for welcoming me into EMG discussions, for the time and ing illustrations and your patience through countless adjustments. Your encouragement you gave me at Staven Kysthospital, and for kindly ability to translate complex ideas into clear, compelling visuals has checking the Norwegian summary of this thesis. greatly enriched this thesis. Michael Miller, my mentor at University of Lund. You were there when Guðni Olafsson, graphic designer. I am so grateful for your work on the it started, the exploration of feet, trunk, and EMG, your encouragement, splendid layout of this thesis. Your sense of detail and design has made insight, and structure provided me with direction. Warm thanks also to it not only professional but also genuinely pleasing to the eye, turning you and Ann for your hospitality in Löberöd during my years in Lund. the text into a book that I am proud to present. Helena Brisby, former head of the Department of Orthopedics at the Koen Simons, statistician . You lured me into the world of Bayesian Institute of Clinical Sciences, Sahlgrenska Academy, University of statistics, something I was initially wary of but now truly grateful for. Gothenburg. Thank you for accepting my thesis proposal. I so appreciate all the effort you put into Study III, and your endless patience and wonderfully pedagogical way of guiding me through my Ola Rolfson, current head of the Department of Orthopedics at the many questions. Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg for granting me the opportunity to pursue my doctoral Fysio Forum, my workplace-a small physical therapy clinic with space studies within the Institute of Clinical Sciences. for the individual and time to care. Daily encounters with patients have grounded me in the realities of clinical practice while providing the Pernilla Eliasson, head of the Orthopedic Research Unit at the inspiration and support to pursue my academic journey. In the balance Department of Orthopedics, Sahlgrenska University Hospital. Thank between hands-on care and scientific curiosity, my work has found its you for making space for this research to happen and for your generous purpose. support in seeing it through. Anna Kimming, friend and fellow physical therapist. From the feet Linda Johansson, Cina Holmer, Anna Orosz and Maya Daneva, upward, your perspective has always been grounded, insightful, and administrators at the Institute of Clinical Sciences Sahlgrenska human. Thank you for your unwavering support, your keen interest, Academy, University of Gothenburg. Thank you for your invaluable and your deep-rooted commitment to the wellbeing of others. From guidance in navigating the winding administrative landscape behind the hands-on treatment to clinical reasoning and sharp observation, your academic requirements of this thesis, and for keeping me well on track enthusiasm and endurance have been a constant source of inspiration. throughout the process. We walked side by side through OMT 3 and the Master’s program in Lund-you always a step ahead, always generous with your notes and assignments. I’m deeply grateful for your companionship on this journey. 130 ACKNOWLEDGEMENT KARI HUSETH 131 To all young athletes, and especially Onsala BK F04, with whom I had The studies presented is this thesis was supported by Felix Neubergh the privilege of being involved for many years. To Niklas Legnedal, for Foundation, IngaBritt and Arne Lundberg Research Foundation and shared attitude toward children’s sport, skill development, and the joy Hemborgs Minnesfond. This work was also supported by grants from of movement. To all sport collaborations in Halland; especially to the LUA/ALF (Local Research and Development Grants and the Swedish Nätverk för kvinnliga ledare and Anna Lundkvist for exchanging Government–Region Agreement on Medical Education and Clinical knowledge and perspectives, for good food, and for many guffaws-for Research). inspiration and restoration. A heartfelt thank you to you all. This is where science comes alive! Randi and Bjørn, dearest mother and father. My deepest gratitude for allowing me to be myself. Thank you for your love and steady support. You taught me to value the forest and the ocean, books and music and art-but most of all, to value people. You expected me to become something, not in any particular form, but with integrity. The foundation you gave me shaped a life view grounded in curiosity, joy, and kindness toward others-values that have quietly guided every step of this thesis. Ida and Anna, my daughters-my little penguins, now grown women. You keep me connected to real life and never hesitate to point out when I’m off track. Your humor, care and love are the heartbeat of my days. No matter where life’s paths take us, my love follows-to the moon and back. Ulrika, my wife and my anchor. This was definitely not your road taken, and let’s be honest: saying you’ve enjoyed every moment of my academic journey would be a bit of a stretch. But through it all, you’ve stayed. With patience, and just enough enthusiasm to keep me going- and a love that held me together when I was coming apart. Life without you wouldn’t be life at all. And yes, in the end-the greatest of these is love ****. * T.S. Eliot ** Robert Frost *** Morticia Addams, by Charles Addams  **** 1 Corinthians 13:13 132 ACKNOWLEDGEMENT KARI HUSETH 133 To all young athletes, and especially Onsala BK F04, with whom I had The studies presented is this thesis was supported by Felix Neubergh the privilege of being involved for many years. To Niklas Legnedal, for Foundation, IngaBritt and Arne Lundberg Research Foundation and shared attitude toward children’s sport, skill development, and the joy Hemborgs Minnesfond. This work was also supported by grants from of movement. To all sport collaborations in Halland; especially to the LUA/ALF (Local Research and Development Grants and the Swedish Nätverk för kvinnliga ledare and Anna Lundkvist for exchanging Government–Region Agreement on Medical Education and Clinical knowledge and perspectives, for good food, and for many guffaws-for Research). inspiration and restoration. A heartfelt thank you to you all. This is where science comes alive! Randi and Bjørn, dearest mother and father. My deepest gratitude for allowing me to be myself. Thank you for your love and steady support. You taught me to value the forest and the ocean, books and music and art-but most of all, to value people. You expected me to become something, not in any particular form, but with integrity. The foundation you gave me shaped a life view grounded in curiosity, joy, and kindness toward others-values that have quietly guided every step of this thesis. Ida and Anna, my daughters-my little penguins, now grown women. You keep me connected to real life and never hesitate to point out when I’m off track. Your humor, care and love are the heartbeat of my days. No matter where life’s paths take us, my love follows-to the moon and back. Ulrika, my wife and my anchor. This was definitely not your road taken, and let’s be honest: saying you’ve enjoyed every moment of my academic journey would be a bit of a stretch. But through it all, you’ve stayed. With patience, and just enough enthusiasm to keep me going- and a love that held me together when I was coming apart. Life without you wouldn’t be life at all. And yes, in the end-the greatest of these is love ****. * T.S. Eliot ** Robert Frost *** Morticia Addams, by Charles Addams  **** 1 Corinthians 13:13 132 ACKNOWLEDGEMENT KARI HUSETH 133 14. References 1. Winter DA. Biomechanics and Motor Control of Human Movement. 4th ed. New Jersey: John Wiely and Sons; 2009. 2. Alexander RM. Energy-saving mechanisms in walking and running. Journal of experimental biology. 1991;160(1):55-69. 3. Gardner GE. The Story of the Human Body: Evolution, Health, and Disease, by Daniel E. Lieberman. University of California Press USA; 2014. 4. Shumway-Cook A, Woollacott MH. Motor Control, Translanting Research into Clinical Practice. 3rd ed. Baltimore: Lippincott Williams and Wilikins; 2007. 5. Gray H, Carter HV, Ukray M. Gray’s Anatomy:(Illustrated With 1247 Coloured Well Drawing Engrawings). E-Kitap Projesi & Cheapest Books; 2023. 6. Latash ML. Fundamentals of motor control. Academic Press; 2012. 7. World Confederation for Physical Therapy. Policy statement: description of physical therapy. World Confederation for Physical Therapy, 2011. https://world.physio/policy/ps-descriptionPT 8. APTA. Standards of Practice for Physical Therapy. 2020. https://www.apta.org/ siteassets/pdfs/policies/standards-of-practice-pt.pdf 9. World Confederation for Physical Therapy. “Description of physical therapy: Policy statement.” (2019). https://world.physio/sites/default/files/2020-04/ PS-2019-Description-of-physical-therapy.pdf 10. Basmajian J, de Luca CJ. Muscles alive. Their Function Revealed by Electromyography. 5th ed. Baltimore, USA: Williams and Wilkins; 1985. 11. Everett T, Kell C. Human movement: an introductory text. 6th ed. Edinburgh: Churchill Livingstone; 2010. 12. Piscitelli D, Falaki A, Solnik S, Latash ML. Anticipatory postural adjustments and anticipatory synergy adjustments: preparing to a postural perturbation with predictable and unpredictable direction. Exp Brain Res. 2017;235(3):713-30. Say not, ‘I have found the truth,’ but rather, ‘I have found a truth.’ 13. Assaiante C, Mallau S, Viel S, Jover M, Schmitz C. Development of postural Say not, ‘I have found the path of the soul.’ Say rather, ‘I have control in healthy children: a functional approach. Neural Plast. 2005;12(2- met the soul walking upon my path. 3):109-18; discussion 263-72. 👥👥 KAHLIL GIBRAN 134 REFERENCES KARI HUSETH 135 14. References 1. Winter DA. Biomechanics and Motor Control of Human Movement. 4th ed. New Jersey: John Wiely and Sons; 2009. 2. Alexander RM. Energy-saving mechanisms in walking and running. Journal of experimental biology. 1991;160(1):55-69. 3. Gardner GE. The Story of the Human Body: Evolution, Health, and Disease, by Daniel E. Lieberman. University of California Press USA; 2014. 4. Shumway-Cook A, Woollacott MH. Motor Control, Translanting Research into Clinical Practice. 3rd ed. Baltimore: Lippincott Williams and Wilikins; 2007. 5. Gray H, Carter HV, Ukray M. Gray’s Anatomy:(Illustrated With 1247 Coloured Well Drawing Engrawings). E-Kitap Projesi & Cheapest Books; 2023. 6. Latash ML. Fundamentals of motor control. Academic Press; 2012. 7. World Confederation for Physical Therapy. Policy statement: description of physical therapy. World Confederation for Physical Therapy, 2011. https://world.physio/policy/ps-descriptionPT 8. APTA. Standards of Practice for Physical Therapy. 2020. https://www.apta.org/ siteassets/pdfs/policies/standards-of-practice-pt.pdf 9. World Confederation for Physical Therapy. “Description of physical therapy: Policy statement.” (2019). https://world.physio/sites/default/files/2020-04/ PS-2019-Description-of-physical-therapy.pdf 10. Basmajian J, de Luca CJ. Muscles alive. Their Function Revealed by Electromyography. 5th ed. Baltimore, USA: Williams and Wilkins; 1985. 11. Everett T, Kell C. Human movement: an introductory text. 6th ed. Edinburgh: Churchill Livingstone; 2010. 12. Piscitelli D, Falaki A, Solnik S, Latash ML. Anticipatory postural adjustments and anticipatory synergy adjustments: preparing to a postural perturbation with predictable and unpredictable direction. Exp Brain Res. 2017;235(3):713-30. Say not, ‘I have found the truth,’ but rather, ‘I have found a truth.’ 13. Assaiante C, Mallau S, Viel S, Jover M, Schmitz C. Development of postural Say not, ‘I have found the path of the soul.’ Say rather, ‘I have control in healthy children: a functional approach. Neural Plast. 2005;12(2- met the soul walking upon my path. 3):109-18; discussion 263-72. 👥👥 KAHLIL GIBRAN 134 REFERENCES KARI HUSETH 135 14. Müller H, Sternad D. Motor learning: changes in the structure of variability in a 27. Madeleine P, Farina D. Time to task failure in shoulder elevation is associated redundant task. Adv Exp Med Biol. 2009;629:439-56. to increase in amplitude and to spatial heterogeneity of upper trapezius mechanomyographic signals. Eur J Appl Physiol. 2008;102(3):325-33. 15. Fetters L. Perspective on variability in the development of human action. Phys Ther. 2010;90(12):1860-7. 28. Farina D, Merletti R, Enoka RM. The extraction of neural strategies from the surface EMG. J Appl Physiol (1985). 2004;96(4):1486-95. 16. Madeleine P, Voigt M, Mathiassen SE. The size of cycle-to-cycle variability in biomechanical exposure among butchers performing a standardised cutting 29. Jandacka D, Blaschova D, Amado A, van Emmerik R, Silvernail JF, Hamill task. Ergonomics. 2008;51(7):1078-95. J. Coordination variability in runners after surgical Achilles tendon repair. Translational Sports Medicine. 2021;4(2):204-13. 17. Komar J, Seifert L, Thouvarecq R. What variability tells us about motor expertise: measurements and perspectives from a complex system approach. Mov Sport 30. Levangie PK, Norkin CC. Joint structure and function: a comprehensive Sci Sci Motric. 2015;89(3):65-77. analysis. 5th ed. Philadelphia: F.A. Davis; 2011. 18. Srinivasan D, Rudolfsson T, Mathiassen SE. Between- and within-subject 31. Smith LK, Weiss EL, Lehmkuhl LD. Brunnstrom’s clinical kinesiology. 5th ed. variance of motor variability metrics in females performing repetitive upper- Philadelphia: F.A. Davis Company; 1996. extremity precision work. J Electromyogr Kinesiol. 2015;25(1):121-9. 32. Perry J, Burnfield J. Gait Analysis: Normal and Pathological Function. 2nd ed. 19. Hatze H. Motion variability-its definition, quantification, and origin. J Mot Behav. Boca Raton: CRC Press; 2024. 1986;18(1):5-16. 33. Saeterbakken AH, Fimland MS. Muscle activity of the core during bilateral, 20. Latash ML. The bliss (not the problem) of motor abundance (not redundancy). unilateral, seated and standing resistance exercise. European journal of applied Experimental brain research. 2012;217(1):1-5. physiology. 2012;112(5):1671-8. 21. Bongaardt R, Meijer OG. Bernstein’s theory of movement behavior: historical 34. Escamilla RF, Lewis C, Pecson A, Imamura R, Andrews JR. Muscle activation development and contemporary relevance. J Mot Behav. 2000;32(1):57-71. among supine, prone, and side position exercises with and without a Swiss ball. Sports Health. 2016;8(4):372-9. 22. Davids K, Bennett S, Newell KM. Movement system variability. Champaign (IL): Human Kinetics; 2006. 35. Clarke B, Al-Hammdany JK, Di Giulio I. Human muscle and spinal activation in response to body weight loading. J Anat. 2023;242(5):745-53. 23. Riley MA, Turvey MT. Variability and determinism in motor behavior. J Mot Behav. 2002;34(2):99-125. 36. Kapandji A, Owerko C, Anderson A. The physiology of the joints. 7th ed. London: Handspring Publishing Limited; 2019. 24. Bartlett R, Wheat J, Robins M. Is movement variability important for sports biomechanists? Sports Biomech. 2007;6(2):224-43. 37. Alexander RM. Simple models of human movement. London: Taylor & Francis; 1995. 25. Simonsen EB, Alkjær T. The variability problem of normal human walking. Med Eng Phys. 2012;34(2):219-24. 38. Kuo AD, Donelan JM, Ruina A. Energetic consequences of walking like an inverted pendulum: step-to-step transitions. Exercise and sport sciences 26. Abboud J, Nougarou F, Pagé I, Cantin V, Massicotte D, Descarreaux M. Trunk reviews. 2005;33(2):88-97. motor variability in patients with non-specific chronic low back pain. Eur J Appl Physiol. 2014;114(12):2645-54. 39. Novacheck TF. The biomechanics of running. Gait Posture. 1998;7(1):77-95. 136 REFERENCES KARI HUSETH 137 14. Müller H, Sternad D. Motor learning: changes in the structure of variability in a 27. Madeleine P, Farina D. Time to task failure in shoulder elevation is associated redundant task. Adv Exp Med Biol. 2009;629:439-56. to increase in amplitude and to spatial heterogeneity of upper trapezius mechanomyographic signals. Eur J Appl Physiol. 2008;102(3):325-33. 15. Fetters L. Perspective on variability in the development of human action. Phys Ther. 2010;90(12):1860-7. 28. Farina D, Merletti R, Enoka RM. The extraction of neural strategies from the surface EMG. J Appl Physiol (1985). 2004;96(4):1486-95. 16. Madeleine P, Voigt M, Mathiassen SE. The size of cycle-to-cycle variability in biomechanical exposure among butchers performing a standardised cutting 29. Jandacka D, Blaschova D, Amado A, van Emmerik R, Silvernail JF, Hamill task. Ergonomics. 2008;51(7):1078-95. J. Coordination variability in runners after surgical Achilles tendon repair. Translational Sports Medicine. 2021;4(2):204-13. 17. Komar J, Seifert L, Thouvarecq R. What variability tells us about motor expertise: measurements and perspectives from a complex system approach. Mov Sport 30. Levangie PK, Norkin CC. Joint structure and function: a comprehensive Sci Sci Motric. 2015;89(3):65-77. analysis. 5th ed. Philadelphia: F.A. Davis; 2011. 18. Srinivasan D, Rudolfsson T, Mathiassen SE. Between- and within-subject 31. Smith LK, Weiss EL, Lehmkuhl LD. Brunnstrom’s clinical kinesiology. 5th ed. variance of motor variability metrics in females performing repetitive upper- Philadelphia: F.A. Davis Company; 1996. extremity precision work. J Electromyogr Kinesiol. 2015;25(1):121-9. 32. Perry J, Burnfield J. Gait Analysis: Normal and Pathological Function. 2nd ed. 19. Hatze H. Motion variability-its definition, quantification, and origin. J Mot Behav. Boca Raton: CRC Press; 2024. 1986;18(1):5-16. 33. Saeterbakken AH, Fimland MS. Muscle activity of the core during bilateral, 20. Latash ML. The bliss (not the problem) of motor abundance (not redundancy). unilateral, seated and standing resistance exercise. European journal of applied Experimental brain research. 2012;217(1):1-5. physiology. 2012;112(5):1671-8. 21. Bongaardt R, Meijer OG. Bernstein’s theory of movement behavior: historical 34. Escamilla RF, Lewis C, Pecson A, Imamura R, Andrews JR. Muscle activation development and contemporary relevance. J Mot Behav. 2000;32(1):57-71. among supine, prone, and side position exercises with and without a Swiss ball. Sports Health. 2016;8(4):372-9. 22. Davids K, Bennett S, Newell KM. Movement system variability. Champaign (IL): Human Kinetics; 2006. 35. Clarke B, Al-Hammdany JK, Di Giulio I. Human muscle and spinal activation in response to body weight loading. J Anat. 2023;242(5):745-53. 23. Riley MA, Turvey MT. Variability and determinism in motor behavior. J Mot Behav. 2002;34(2):99-125. 36. Kapandji A, Owerko C, Anderson A. The physiology of the joints. 7th ed. London: Handspring Publishing Limited; 2019. 24. Bartlett R, Wheat J, Robins M. Is movement variability important for sports biomechanists? Sports Biomech. 2007;6(2):224-43. 37. Alexander RM. Simple models of human movement. London: Taylor & Francis; 1995. 25. Simonsen EB, Alkjær T. The variability problem of normal human walking. Med Eng Phys. 2012;34(2):219-24. 38. Kuo AD, Donelan JM, Ruina A. Energetic consequences of walking like an inverted pendulum: step-to-step transitions. Exercise and sport sciences 26. Abboud J, Nougarou F, Pagé I, Cantin V, Massicotte D, Descarreaux M. Trunk reviews. 2005;33(2):88-97. motor variability in patients with non-specific chronic low back pain. Eur J Appl Physiol. 2014;114(12):2645-54. 39. Novacheck TF. The biomechanics of running. Gait Posture. 1998;7(1):77-95. 136 REFERENCES KARI HUSETH 137 40. Cavagna GA, Saibene FP, Margaria R. Mechanical work in running. Journal of 52. Józsa L, Kannus P. Human tendons: anatomy, physiology, and pathology. applied physiology. 1964;19(2):249-56. Champaign (IL): Human Kinetics; 1997. 41. Hoitz F, von Tscharner V, Baltich J, Nigg BM. Individuality decoded by running 53. Malvankar S, Khan WS. Evolution of the Achilles tendon: the athlete’s Achilles patterns: movement characteristics that determine the uniqueness of human heel? Foot (Edinb). 2011;21(4):193-7. running. PLoS One. 2021;16(4):e0249657. 54. Fukunaga T, Kubo K, Kawakami Y, Fukashiro S, Kanehisa H, Maganaris CN. 42. Bramble DM, Lieberman DE. Endurance running and the evolution of Homo. In vivo behaviour of human muscle tendon during walking. Proc Biol Sci. Nature. 2004;432(7015):345-52. 2001;268(1464):229-33. 43. Ker R, Bennett M, Bibby S, Kester R, Alexander RM. The spring in the arch of the 55. Ishikawa M, Komi PV, Grey MJ, Lepola V, Brüggemann GP. Muscle–tendon human foot. Nature. 1987;325(6100):147-9. interaction and elastic energy usage in human walking. J Appl Physiol (1985). 2005;99(2):603-8. 44. Nigg BM, Herzog W. Biomechanics of the musculoskeletal system. 3rd ed. Chichester (UK): John Wiley & Sons Ltd; 2006. 56. Komi PV, Fukashiro S, Järvinen M. Biomechanical loading of Achilles tendon during normal locomotion. Clin Sports Med. 1992;11(3):521-31. 45. Standring S, Ellis H, Healy JC, Johnson D, Williams A, Collins P, et al. Gray’s anatomy: the anatomical basis of clinical practice. 39th ed. Edinburgh: Elsevier 57. Maffulli N, Almekinders LC. The Achilles tendon. London: Springer; 2007. Churchill Livingstone; 2005. 58. Edama M, Kubo M, Onishi H, Takabayashi T, Inai T, Yokoyama E, et al. The 46. Levine D, Whittle MW. The effects of pelvic movement on lumbar lordosis in the twisted structure of the human Achilles tendon. Scand J Med Sci Sports. standing position. J Orthop Sports Phys Ther. 1996;24(3):130-5. 2015;25(5):497-503. 47. Yoo HJ, Sim T, Choi A, Park HJ, Yang H, Heo HM, et al. Quantifying coordination 59. Pękala P, Henry B, Ochała A, Kopacz P, Tatoń G, Młyniec A, et al. The twisted between agonist and antagonist muscles during gait. J Mech Sci Technol. structure of the Achilles tendon unraveled: a detailed quantitative and qualitative 2016;30(11):5321-8. anatomical investigation. Scand J Med Sci Sports. 2017;27(12):1705-15. 48. Tengman T, Riad J. Three-dimensional gait analysis following Achilles tendon 60. Arndt A, Bengtsson AS, Peolsson M, Thorstensson A, Movin T. Non-uniform rupture with nonsurgical treatment reveals long-term deficiencies in muscle displacement within the Achilles tendon during passive ankle joint motion. strength and function. Orthop J Sports Med. 2013;1(4):2325967113504734. Knee Surg Sports Traumatol Arthrosc. 2012;20(9):1868-74. 49. Willy RW, Brorsson A, Powell HC, Willson JD, Tranberg R, Grävare Silbernagel 61. Magnusson SP, Narici MV, Maganaris CN, Kjaer M. Human tendon behaviour K. Elevated knee joint kinetics and reduced ankle kinetics are present during and adaptation, in vivo. J Physiol. 2008;586(1):71-81. jogging and hopping after Achilles tendon ruptures. Am J Sports Med. 2017;45(5):1124-33. 62. Tarantino D, Palermi S, Sirico F, Corrado B. Achilles tendon rupture: mechanisms of injury, principles of rehabilitation and return to play. J Funct Morphol Kinesiol. 50. Don R, Ranavolo A, Cacchio A, Serrao M, Costabile F, Iachelli M, et al. Relationship 2020;5(4):99. between recovery of calf muscle biomechanical properties and gait pattern following surgery for Achilles tendon rupture. Clin Biomech. 2007;22(2):211-20. 63. Campos PT, da Costa MQ, Lascano GCM. Achilles tendon rupture: discussion and updates [Ruptura do tendão de Aquiles: discussão e atualizações]. J Foot 51. Bojsen-Møller J, Magnusson SP. Heterogeneous loading of the human Achilles Ankle. 2024;18(3):308-14. tendon in vivo. Exerc Sport Sci Rev. 2015;43(4):190-7. 138 REFERENCES KARI HUSETH 139 40. Cavagna GA, Saibene FP, Margaria R. Mechanical work in running. Journal of 52. Józsa L, Kannus P. Human tendons: anatomy, physiology, and pathology. applied physiology. 1964;19(2):249-56. Champaign (IL): Human Kinetics; 1997. 41. Hoitz F, von Tscharner V, Baltich J, Nigg BM. Individuality decoded by running 53. Malvankar S, Khan WS. 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Comparison of selected 2010;25(7):745-8. muscular activity of trunk and lower extremities in young women’s walking on supinated, pronated and normal foot. Apunts Sports Med. 2016;51(189):13-9. 144 REFERENCES KARI HUSETH 145 131. Menz HB, Dufour AB, Riskowski JL, Hillstrom HJ, Hannan MT. Foot posture, 142. Frankewycz B, Penz A, Weber J, da Silva NP, Freimoser F, Bell R, et al. Achilles foot function and low back pain: the Framingham Foot Study. Rheumatology tendon elastic properties remain decreased in the long term after rupture. (Oxford). 2013;52(12):2275-82. Knee Surg Sports Traumatol Arthrosc. 2018;26(7):2080-7. 132. Powers CM, Chen PY, Reischl SF, Perry J. Comparison of foot pronation and 143. Heikkinen J, Lantto I, Flinkkilä T, Ohtonen P, Niinimäki J, Siira P, et al. Soleus lower extremity rotation in persons with and without patellofemoral pain. Foot atrophy is common after the nonsurgical treatment of acute Achilles tendon Ankle Int. 2002;23(7):634-40. ruptures: a randomized clinical trial comparing surgical and nonsurgical functional treatments. Am J Sports Med. 2017;45(6):1395-404. 133. Chuter V, Spink M, Searle A, Ho A. The effectiveness of shoe insoles for the prevention and treatment of low back pain: a systematic review and 144. Heikkinen J, Lantto I, Piilonen J, Flinkkilä T, Ohtonen P, Siira P, et al. Tendon meta-analysis of randomised controlled trials. BMC Musculoskelet Disord. length, calf muscle atrophy, and strength deficit after acute Achilles tendon 2014;15:140. rupture: long-term follow-up of patients in a previous study. J Bone Joint Surg Am. 2017;99(18):1509-15. 134. Sadler S, Spink M, Lanting S, Chuter V. A randomised controlled trial investigating the effect of foot orthoses for the treatment of chronic nonspecific low back 145. Winter DA. Biomechanics and motor control of human gait: normal, elderly and pain. Musculoskelet Care. 2023;21(3):856-64. pathological. 2nd ed. Waterloo (ON): University of Waterloo Press; 1991. 135. Bayıroğlu G, Pisirici P, Feyzioğlu Ö. The effect of different subtalar joint pronation 146. Carmont MR, Gunnarsson B, Brorsson A, Nilsson-Helander K. Musculotendinous amounts on postural stability, function and lower extremity alignment in healthy ruptures of the Achilles tendon have greater heel-rise height index compared individuals. Foot. 2024;60:102123. with mid-substance ruptures with nonoperative management: a retrospective cohort study. J ISAKOS. 2024;9(2):148-52. 136. Dananberg HJ, Guiliano M. Chronic low-back pain and its response to custom- made foot orthoses. J Am Podiatr Med Assoc. 1999;89(3):109-17. 147. Srinivasan D, Mathiassen SE. Motor variability in occupational health and performance. Clin Biomech. 2012;27(10):979-93. 137. Nigg BM, Nigg S, Hoitz F, Subramanium A, Vienneau J, Wannop JW, et al. Highlighting the present state of biomechanics in shoe research (2000–2023). 148. Davids K, Glazier P, Araújo D, Bartlett R. Movement systems as dynamical Footwear Sci. 2023;15(2):133-43. systems: the functional role of variability and its implications for sports medicine. Sports Med. 2003;33(4):245-60. 138. Nakajima T, Sakamoto M, Tazoe T, Endoh T, Komiyama T. Location specificity of plantar cutaneous reflexes involving lower limb muscles in humans. Exp Brain 149. De Luca CJ. The use of surface electromyography in biomechanics. J Appl Res. 2006;175(3):514-25. Biomech. 1997;13(2):135-63. 139. Henry SM, Fung J, Horak FB. EMG responses to maintain stance during 150. Dankaerts W, O’Sullivan PB, Burnett AF, Straker LM, Danneels LA. Reliability multidirectional surface translations. J Neurophysiol. 1998;80(4):1939-50. of EMG measurements for trunk muscles during maximal and submaximal voluntary isometric contractions in healthy controls and CLBP patients. J 140. Hoeffner R, Agergaard AS, Svensson RB, Cullum C, Mikkelsen RK, Konradsen Electromyogr Kinesiol. 2004;14(3):333-42. L, et al. Tendon elongation and function after delayed or standard loading of surgically repaired Achilles tendon ruptures: a randomized controlled trial. Am 151. Mitchell MD, Yarossi MB, Pierce DN, Garbarini EL, Forrest GF. Reliability of J Sports Med. 2024;52(4):1022-31. surface EMG as an assessment tool for trunk activity and potential to determine neurorecovery in SCI. Spinal Cord. 2015;53(5):368-74. 141. Agres AN, Arampatzis A, Gehlen T, Manegold S, Duda GN. Muscle fascicles exhibit limited passive elongation throughout the rehabilitation of Achilles 152. Bogey R, Cerny K, Mohammed O. Repeatability of wire and surface electrodes tendon rupture after percutaneous repair. Front Physiol. 2020;11:746. in gait. Am J Phys Med Rehabil. 2003;82(5):338-44. 146 REFERENCES KARI HUSETH 147 131. Menz HB, Dufour AB, Riskowski JL, Hillstrom HJ, Hannan MT. Foot posture, 142. Frankewycz B, Penz A, Weber J, da Silva NP, Freimoser F, Bell R, et al. Achilles foot function and low back pain: the Framingham Foot Study. Rheumatology tendon elastic properties remain decreased in the long term after rupture. (Oxford). 2013;52(12):2275-82. Knee Surg Sports Traumatol Arthrosc. 2018;26(7):2080-7. 132. Powers CM, Chen PY, Reischl SF, Perry J. Comparison of foot pronation and 143. Heikkinen J, Lantto I, Flinkkilä T, Ohtonen P, Niinimäki J, Siira P, et al. Soleus lower extremity rotation in persons with and without patellofemoral pain. Foot atrophy is common after the nonsurgical treatment of acute Achilles tendon Ankle Int. 2002;23(7):634-40. ruptures: a randomized clinical trial comparing surgical and nonsurgical functional treatments. Am J Sports Med. 2017;45(6):1395-404. 133. Chuter V, Spink M, Searle A, Ho A. The effectiveness of shoe insoles for the prevention and treatment of low back pain: a systematic review and 144. Heikkinen J, Lantto I, Piilonen J, Flinkkilä T, Ohtonen P, Siira P, et al. Tendon meta-analysis of randomised controlled trials. BMC Musculoskelet Disord. length, calf muscle atrophy, and strength deficit after acute Achilles tendon 2014;15:140. rupture: long-term follow-up of patients in a previous study. J Bone Joint Surg Am. 2017;99(18):1509-15. 134. Sadler S, Spink M, Lanting S, Chuter V. A randomised controlled trial investigating the effect of foot orthoses for the treatment of chronic nonspecific low back 145. Winter DA. Biomechanics and motor control of human gait: normal, elderly and pain. Musculoskelet Care. 2023;21(3):856-64. pathological. 2nd ed. Waterloo (ON): University of Waterloo Press; 1991. 135. Bayıroğlu G, Pisirici P, Feyzioğlu Ö. The effect of different subtalar joint pronation 146. Carmont MR, Gunnarsson B, Brorsson A, Nilsson-Helander K. Musculotendinous amounts on postural stability, function and lower extremity alignment in healthy ruptures of the Achilles tendon have greater heel-rise height index compared individuals. Foot. 2024;60:102123. with mid-substance ruptures with nonoperative management: a retrospective cohort study. J ISAKOS. 2024;9(2):148-52. 136. Dananberg HJ, Guiliano M. Chronic low-back pain and its response to custom- made foot orthoses. J Am Podiatr Med Assoc. 1999;89(3):109-17. 147. Srinivasan D, Mathiassen SE. Motor variability in occupational health and performance. Clin Biomech. 2012;27(10):979-93. 137. Nigg BM, Nigg S, Hoitz F, Subramanium A, Vienneau J, Wannop JW, et al. Highlighting the present state of biomechanics in shoe research (2000–2023). 148. Davids K, Glazier P, Araújo D, Bartlett R. Movement systems as dynamical Footwear Sci. 2023;15(2):133-43. systems: the functional role of variability and its implications for sports medicine. Sports Med. 2003;33(4):245-60. 138. Nakajima T, Sakamoto M, Tazoe T, Endoh T, Komiyama T. Location specificity of plantar cutaneous reflexes involving lower limb muscles in humans. Exp Brain 149. De Luca CJ. The use of surface electromyography in biomechanics. J Appl Res. 2006;175(3):514-25. Biomech. 1997;13(2):135-63. 139. Henry SM, Fung J, Horak FB. EMG responses to maintain stance during 150. Dankaerts W, O’Sullivan PB, Burnett AF, Straker LM, Danneels LA. Reliability multidirectional surface translations. J Neurophysiol. 1998;80(4):1939-50. of EMG measurements for trunk muscles during maximal and submaximal voluntary isometric contractions in healthy controls and CLBP patients. J 140. Hoeffner R, Agergaard AS, Svensson RB, Cullum C, Mikkelsen RK, Konradsen Electromyogr Kinesiol. 2004;14(3):333-42. L, et al. Tendon elongation and function after delayed or standard loading of surgically repaired Achilles tendon ruptures: a randomized controlled trial. Am 151. Mitchell MD, Yarossi MB, Pierce DN, Garbarini EL, Forrest GF. Reliability of J Sports Med. 2024;52(4):1022-31. surface EMG as an assessment tool for trunk activity and potential to determine neurorecovery in SCI. Spinal Cord. 2015;53(5):368-74. 141. Agres AN, Arampatzis A, Gehlen T, Manegold S, Duda GN. Muscle fascicles exhibit limited passive elongation throughout the rehabilitation of Achilles 152. Bogey R, Cerny K, Mohammed O. Repeatability of wire and surface electrodes tendon rupture after percutaneous repair. Front Physiol. 2020;11:746. in gait. Am J Phys Med Rehabil. 2003;82(5):338-44. 146 REFERENCES KARI HUSETH 147 153. Camomilla V, Donati M, Stagni R, Cappozzo A. Noninvasive assessment of 163. Tyni-Lenné R. To identify the physiotherapy paradigm: a challenge for the superficial soft tissue local displacements during movement: a feasibility future. In: Andersson GBJ, Hobart DJ, editors. International perspectives in study. J Biomech. 2009;42(7):931-7. physical therapy. London: Taylor & Francis; 1989. p. 169-70. 154. Zügner R, Tranberg R, Lisovskaja V, Shareghi B, Kärrholm J. Validation of gait 164. Rowe R, Tichenor C, Bell S, Boissonnault W, King P, Kulig K. Orthopaedic manual analysis with dynamic radiostereometric analysis (RSA) in patients operated physical therapy: description of advanced specialty practice. Tallahassee (FL): with total hip arthroplasty. J Orthop Res. 2017;35(7):1515-22. American Academy of Orthopaedic Manual Physical Therapists; 2008. 155. Zügner R, Tranberg R, Lisovskaja V, Kärrholm J. Different reliability of 165. Lin I, Wiles L, Waller R, Goucke R, Nagree Y, Gibberd M, et al. What does instrumented gait analysis between patients with unilateral hip osteoarthritis, best practice care for musculoskeletal pain look like? Eleven consistent unilateral hip prosthesis and healthy controls. BMC Musculoskelet Disord. recommendations from high-quality clinical practice guidelines: systematic 2018;19(1):224. review. Br J Sports Med. 2020;54(2):79-86. 156. Fändriks A, Zügner R, Shareghi B, Kärrholm J, Tranberg R. Skin and cluster 166. Sharma P, Maffulli N. Biology of tendon injury: healing, modeling and remodeling. markers underestimate knee flexion during controlled motions: evaluation of 12 J Musculoskelet Neuronal Interact. 2006;6(2):181-90. patients with knee arthroplasty using radiostereometric analysis as reference. J Biomech. 2025;182:112591. 157. World Medical Association. Human experimentation: code of ethics of the World Medical Association. Declaration of Helsinki. Br Med J. 1964;2(5402):177. 158. ALLEA – All European Academies. The European Code of Conduct for Research Integrity [Internet]. Revised edition. Berlin: ALLEA; 2017. https://allea.org/code- of-conduct/ 159. Larsson E, Brorsson A, Carling M, Johansson C, Carmont MR, Nilsson Helander K. Sex differences in patients’ recovery following an acute Achilles tendon rupture: a large cohort study. BMC Musculoskelet Disord. 2022;23(1):913. 160. Larsson E, Nilsson N, Walstern J, Brorsson A, Nilsson Helander K. Females present larger deficit in heel-rise height at 3 months following an Achilles tendon rupture compared with males. Knee Surg Sports Traumatol Arthrosc. 2024;32(10):2581-88. 161. Alshabrami QM, Almansour BI, Al Shammari RA, Hameyd AY, Alabdelqader WF, Alenizy NF, et al. The use of physical therapy in managing sports injuries. J Int Crisis Risk Commun Res. 2024;7(S1-1):538. 162. Kerry R, Young KJ, Evans DW, Lee E, Georgopoulos V, Meakins A, et al. A modern way to teach and practice manual therapy. Chiropr Man Therap. 2024;32(1):17. 148 REFERENCES KARI HUSETH 149 153. Camomilla V, Donati M, Stagni R, Cappozzo A. Noninvasive assessment of 163. Tyni-Lenné R. To identify the physiotherapy paradigm: a challenge for the superficial soft tissue local displacements during movement: a feasibility future. In: Andersson GBJ, Hobart DJ, editors. International perspectives in study. J Biomech. 2009;42(7):931-7. physical therapy. London: Taylor & Francis; 1989. p. 169-70. 154. Zügner R, Tranberg R, Lisovskaja V, Shareghi B, Kärrholm J. Validation of gait 164. Rowe R, Tichenor C, Bell S, Boissonnault W, King P, Kulig K. Orthopaedic manual analysis with dynamic radiostereometric analysis (RSA) in patients operated physical therapy: description of advanced specialty practice. Tallahassee (FL): with total hip arthroplasty. J Orthop Res. 2017;35(7):1515-22. American Academy of Orthopaedic Manual Physical Therapists; 2008. 155. Zügner R, Tranberg R, Lisovskaja V, Kärrholm J. Different reliability of 165. Lin I, Wiles L, Waller R, Goucke R, Nagree Y, Gibberd M, et al. What does instrumented gait analysis between patients with unilateral hip osteoarthritis, best practice care for musculoskeletal pain look like? Eleven consistent unilateral hip prosthesis and healthy controls. BMC Musculoskelet Disord. recommendations from high-quality clinical practice guidelines: systematic 2018;19(1):224. review. Br J Sports Med. 2020;54(2):79-86. 156. Fändriks A, Zügner R, Shareghi B, Kärrholm J, Tranberg R. Skin and cluster 166. Sharma P, Maffulli N. Biology of tendon injury: healing, modeling and remodeling. markers underestimate knee flexion during controlled motions: evaluation of 12 J Musculoskelet Neuronal Interact. 2006;6(2):181-90. patients with knee arthroplasty using radiostereometric analysis as reference. J Biomech. 2025;182:112591. 157. World Medical Association. Human experimentation: code of ethics of the World Medical Association. Declaration of Helsinki. Br Med J. 1964;2(5402):177. 158. ALLEA – All European Academies. The European Code of Conduct for Research Integrity [Internet]. Revised edition. Berlin: ALLEA; 2017. https://allea.org/code- of-conduct/ 159. Larsson E, Brorsson A, Carling M, Johansson C, Carmont MR, Nilsson Helander K. Sex differences in patients’ recovery following an acute Achilles tendon rupture: a large cohort study. BMC Musculoskelet Disord. 2022;23(1):913. 160. Larsson E, Nilsson N, Walstern J, Brorsson A, Nilsson Helander K. Females present larger deficit in heel-rise height at 3 months following an Achilles tendon rupture compared with males. Knee Surg Sports Traumatol Arthrosc. 2024;32(10):2581-88. 161. Alshabrami QM, Almansour BI, Al Shammari RA, Hameyd AY, Alabdelqader WF, Alenizy NF, et al. The use of physical therapy in managing sports injuries. J Int Crisis Risk Commun Res. 2024;7(S1-1):538. 162. Kerry R, Young KJ, Evans DW, Lee E, Georgopoulos V, Meakins A, et al. A modern way to teach and practice manual therapy. Chiropr Man Therap. 2024;32(1):17. 148 REFERENCES KARI HUSETH 149 15. Appendix Sahlgrenska University Hospital – Occupational Therapy and Physiotherapy Implementation / Physiotherapeutic Treatment Plan Following Acute Achilles Tendon Rupture Applicable to both surgical and non-surgical management Emergency Department (Initial Management): The affected foot is immobilized in a cast in plantarflexion. Provide the patient with the brochure “Information for Patients with Achilles Tendon Injury” and review the prescribed exercises. Advise the patient to avoid placing the foot on the floor whenever possible; the foot should be kept elevated in a horizontal position during rest to minimize swelling. When standing (e.g., for hygiene, dressing, or food preparation), the foot may rest lightly on the floor for balance. The patient should off-load the injured leg using two crutches. Gait should involve active hip and knee movement on the affected side without weight-bearing on the foot. Patients with impaired balance may require a walking aid (e.g., Beta crutch), and in some cases, a wheelchair. Toe-touching the ground with the injured foot may aid in balance. 2 Weeks Post-Injury: At the orthopedic outpatient follow-up, the cast is replaced with an orthosis, which must be worn at all times, including during showering. My coach said I run like a girl, and I said if he ran a little faster, he could too. Instruct in the home exercise program “Achilles Tendon Program I.” 👥👥 MIA HAMM 150 APPENDIX KARI HUSETH 151 15. Appendix Sahlgrenska University Hospital – Occupational Therapy and Physiotherapy Implementation / Physiotherapeutic Treatment Plan Following Acute Achilles Tendon Rupture Applicable to both surgical and non-surgical management Emergency Department (Initial Management): The affected foot is immobilized in a cast in plantarflexion. Provide the patient with the brochure “Information for Patients with Achilles Tendon Injury” and review the prescribed exercises. Advise the patient to avoid placing the foot on the floor whenever possible; the foot should be kept elevated in a horizontal position during rest to minimize swelling. When standing (e.g., for hygiene, dressing, or food preparation), the foot may rest lightly on the floor for balance. The patient should off-load the injured leg using two crutches. Gait should involve active hip and knee movement on the affected side without weight-bearing on the foot. Patients with impaired balance may require a walking aid (e.g., Beta crutch), and in some cases, a wheelchair. Toe-touching the ground with the injured foot may aid in balance. 2 Weeks Post-Injury: At the orthopedic outpatient follow-up, the cast is replaced with an orthosis, which must be worn at all times, including during showering. My coach said I run like a girl, and I said if he ran a little faster, he could too. Instruct in the home exercise program “Achilles Tendon Program I.” 👥👥 MIA HAMM 150 APPENDIX KARI HUSETH 151 Continue to encourage toe mobility. weeks post-injury. Educate the patient to routinely palpate the tendon to monitor for 4 Weeks Post-Injury: signs of overload (increased warmth, redness, swelling). Follow-up with treating physiotherapist. Teach how to remove and reapply the orthosis for hygiene and exercise purposes. Review “Achilles Tendon Program I.” Encourage regular ventilation of the lower leg and provide instructions Assess the tendon: continuity, width, consistency. on cleaning the foot and leg with a washcloth. Perform the Thompson test. Fit the orthosis with three wedges as appropriate (typically smaller Evaluate current tendon loading; if needed, reduce walking volume. wedges). Patients may add a personal insole or silicone heel cup for comfort. Remove the lowest wedge. If tension is felt in the tendon during gait with three wedges, a fourth Retrain gait on flat and stair surfaces. wedge may be added temporarily and removed by the patient after several days based on comfort. Wean off crutches indoors if gait is well-balanced and the tendon is not under excessive strain. Begin full weight-bearing gait training with two crutches. Assess footwear. Heel elevation should remain ≥1.5 cm. Shoes must Practice gait on flat surfaces and stairs if applicable, ensuring no have a heel counter. uncomfortable stretching of the tendon. Determine frequency and location of continued rehab. Recommend a cork wedge in the contralateral shoe to equalize leg length. For patients with special needs, refer to an orthopedic Surgical patients: orthosis can be removed at night and for seated technician for shoe modification. showering (non-weight-bearing). Begin planning for appropriate footwear for use post-orthosis. Indoor Non-surgical patients: orthosis must remain on 24/7. and outdoor shoes should have a heel height differential of at least 1.5 cm. Flat shoes (e.g., sneakers) are not appropriate; both pairs should For surgical cases: monitor wound healing and begin scar mobilization have a heel counter. Shoes can be assessed at the next visit. once healed. Plan for continued physiotherapy. If referred to primary care, ensure All patients may initiate stationary cycling with the orthosis on. Provide the receiving provider is aware of their role in early rehabilitation and training in safe mounting/dismounting. responsible for progressive wedge and orthosis weaning, starting at 8 Surgical patients should avoid excessive sweating in the orthosis until 152 APPENDIX KARI HUSETH 153 Continue to encourage toe mobility. weeks post-injury. Educate the patient to routinely palpate the tendon to monitor for 4 Weeks Post-Injury: signs of overload (increased warmth, redness, swelling). Follow-up with treating physiotherapist. Teach how to remove and reapply the orthosis for hygiene and exercise purposes. Review “Achilles Tendon Program I.” Encourage regular ventilation of the lower leg and provide instructions Assess the tendon: continuity, width, consistency. on cleaning the foot and leg with a washcloth. Perform the Thompson test. Fit the orthosis with three wedges as appropriate (typically smaller Evaluate current tendon loading; if needed, reduce walking volume. wedges). Patients may add a personal insole or silicone heel cup for comfort. Remove the lowest wedge. If tension is felt in the tendon during gait with three wedges, a fourth Retrain gait on flat and stair surfaces. wedge may be added temporarily and removed by the patient after several days based on comfort. Wean off crutches indoors if gait is well-balanced and the tendon is not under excessive strain. Begin full weight-bearing gait training with two crutches. Assess footwear. Heel elevation should remain ≥1.5 cm. Shoes must Practice gait on flat surfaces and stairs if applicable, ensuring no have a heel counter. uncomfortable stretching of the tendon. Determine frequency and location of continued rehab. Recommend a cork wedge in the contralateral shoe to equalize leg length. For patients with special needs, refer to an orthopedic Surgical patients: orthosis can be removed at night and for seated technician for shoe modification. showering (non-weight-bearing). Begin planning for appropriate footwear for use post-orthosis. Indoor Non-surgical patients: orthosis must remain on 24/7. and outdoor shoes should have a heel height differential of at least 1.5 cm. Flat shoes (e.g., sneakers) are not appropriate; both pairs should For surgical cases: monitor wound healing and begin scar mobilization have a heel counter. Shoes can be assessed at the next visit. once healed. Plan for continued physiotherapy. If referred to primary care, ensure All patients may initiate stationary cycling with the orthosis on. Provide the receiving provider is aware of their role in early rehabilitation and training in safe mounting/dismounting. responsible for progressive wedge and orthosis weaning, starting at 8 Surgical patients should avoid excessive sweating in the orthosis until 152 APPENDIX KARI HUSETH 153 the wound is fully healed. Restoration of normal gastrocnemius activation is key to reducing pain, swelling, and optimizing function. 6 Weeks Post-Injury: Each step should promote natural tendon loading and circulation. Follow-up with physiotherapist. Aim for symmetry in step length, stance phase, and muscle activation Repeat assessments: tendon palpation, Thompson test, and loading across joints. evaluation. Continue using one or two crutches until gait is normalized. Remove the next wedge (done by the patient or physiotherapist). Identify and discuss risk factors (e.g., stairs, curbs, inclines, uneven Continue gait training. If discomfort arises, resume use of two terrain). crutches. Advise against walking as exercise; cycling is preferred to stimulate The final wedge remains until orthosis discontinuation at 8 weeks circulation. Compression stockings may also be beneficial. post-injury. Driving should be avoided until coordination and strength are 8 Weeks Post-Injury: sufficient. Follow-up and orthosis weaning. 8–12 Weeks Post-Injury: Repeat tendon assessment, Thompson’s test, and evaluate loading. Ongoing rehabilitation with gradual progression of load and speed, based on individual assessment. Measure Achilles Tendon Resting Angle (ATRA). Focus on restoring automatic, normalized gait pattern. For surgical patients: continue scar evaluation and mobilization. Provide tape application guidance for scar maturation. Crutches should be used until gait mechanics are optimal. Begin “Achilles Tendon Program II.” Seated exercises are performed Balance protection of healing structures with appropriately timed barefoot. loading. During standing/walking, indoors and outdoors, supportive shoes must Many patients benefit from more frequent physiotherapy visits be worn for four weeks post-orthosis. following orthosis discontinuation. Distribute cork wedges for use in both shoes. At 12-week orthopedic follow-up, include completed ATRS (Achilles Tendon Total Rupture Score) and activity level (PAS, Grimby scale). Emphasize gait training with appropriate foot roll-off. 154 APPENDIX KARI HUSETH 155 the wound is fully healed. Restoration of normal gastrocnemius activation is key to reducing pain, swelling, and optimizing function. 6 Weeks Post-Injury: Each step should promote natural tendon loading and circulation. Follow-up with physiotherapist. Aim for symmetry in step length, stance phase, and muscle activation Repeat assessments: tendon palpation, Thompson test, and loading across joints. evaluation. Continue using one or two crutches until gait is normalized. Remove the next wedge (done by the patient or physiotherapist). Identify and discuss risk factors (e.g., stairs, curbs, inclines, uneven Continue gait training. If discomfort arises, resume use of two terrain). crutches. Advise against walking as exercise; cycling is preferred to stimulate The final wedge remains until orthosis discontinuation at 8 weeks circulation. Compression stockings may also be beneficial. post-injury. Driving should be avoided until coordination and strength are 8 Weeks Post-Injury: sufficient. Follow-up and orthosis weaning. 8–12 Weeks Post-Injury: Repeat tendon assessment, Thompson’s test, and evaluate loading. Ongoing rehabilitation with gradual progression of load and speed, based on individual assessment. Measure Achilles Tendon Resting Angle (ATRA). Focus on restoring automatic, normalized gait pattern. For surgical patients: continue scar evaluation and mobilization. Provide tape application guidance for scar maturation. Crutches should be used until gait mechanics are optimal. Begin “Achilles Tendon Program II.” Seated exercises are performed Balance protection of healing structures with appropriately timed barefoot. loading. During standing/walking, indoors and outdoors, supportive shoes must Many patients benefit from more frequent physiotherapy visits be worn for four weeks post-orthosis. following orthosis discontinuation. Distribute cork wedges for use in both shoes. At 12-week orthopedic follow-up, include completed ATRS (Achilles Tendon Total Rupture Score) and activity level (PAS, Grimby scale). Emphasize gait training with appropriate foot roll-off. 154 APPENDIX KARI HUSETH 155 12 Weeks and Beyond: There are two key risks that must be avoided: Continue individualized rehabilitation. Progressively increase load with Re-rupture of the tendon the goal of returning to pre-injury function. Tendon healing with excessive length, which leads to decreased Stretching of the gastrocnemius-soleus complex should be avoided strength before 16 weeks post-injury, as elongation is a major risk for compromised recovery. To minimize these risks: For patients with ankle stiffness, introduce range-of-motion exercises Avoid excessive stretching of the tendon in the early phase. in positions that minimize Achilles tendon stretch (e.g., knee flexed, Stretching occurs when the foot is dorsiflexed (bends upward). foot supported). For the tendon to heal optimally and regain elasticity, gentle and Outdoor cycling can typically begin after 12 weeks, starting cautiously. appropriate activation is essential. Total rehabilitation time ranges from 6–12 months. Example set-up: Orthosis on the left foot, with 3 wedges placed under Sport-specific training may begin at 4–6 months if progress is the grey insole. satisfactory. Return to high-impact sport typically requires 9–12 months. Exercise 1 Full tendon tensile strength is generally not regained until 12 months Ankle plantarflexion in prone or sitting post-injury. Position: Foot – Achilles Tendon Program I Home Exercise Program Lying face down with your feet hanging off the edge of a bed, or Sahlgrenska University Hospital – Occupational Therapy and Physiotherapy Sitting with the lower leg supported and knee straight Instructions: Action: During the first 6 weeks while wearing the orthosis, remove it 3–5 times daily to perform these exercises. Point the foot down (plantarflex), then slowly return to a relaxed position. Important Considerations During Rehabilitation Following Achilles Tendon Rupture: Dosage: 3 sets of 20 repetitions 156 APPENDIX KARI HUSETH 157 12 Weeks and Beyond: There are two key risks that must be avoided: Continue individualized rehabilitation. Progressively increase load with Re-rupture of the tendon the goal of returning to pre-injury function. Tendon healing with excessive length, which leads to decreased Stretching of the gastrocnemius-soleus complex should be avoided strength before 16 weeks post-injury, as elongation is a major risk for compromised recovery. To minimize these risks: For patients with ankle stiffness, introduce range-of-motion exercises Avoid excessive stretching of the tendon in the early phase. in positions that minimize Achilles tendon stretch (e.g., knee flexed, Stretching occurs when the foot is dorsiflexed (bends upward). foot supported). For the tendon to heal optimally and regain elasticity, gentle and Outdoor cycling can typically begin after 12 weeks, starting cautiously. appropriate activation is essential. Total rehabilitation time ranges from 6–12 months. Example set-up: Orthosis on the left foot, with 3 wedges placed under Sport-specific training may begin at 4–6 months if progress is the grey insole. satisfactory. Return to high-impact sport typically requires 9–12 months. Exercise 1 Full tendon tensile strength is generally not regained until 12 months Ankle plantarflexion in prone or sitting post-injury. Position: Foot – Achilles Tendon Program I Home Exercise Program Lying face down with your feet hanging off the edge of a bed, or Sahlgrenska University Hospital – Occupational Therapy and Physiotherapy Sitting with the lower leg supported and knee straight Instructions: Action: During the first 6 weeks while wearing the orthosis, remove it 3–5 times daily to perform these exercises. Point the foot down (plantarflex), then slowly return to a relaxed position. Important Considerations During Rehabilitation Following Achilles Tendon Rupture: Dosage: 3 sets of 20 repetitions 156 APPENDIX KARI HUSETH 157 This safely activates the calf muscle while the wedges protect the tendon from stretching. Exercise 2 Dosage: Side-to-side ankle movement 2 sets of 10 repetitions Position: Seated or lying face down as in Exercise 1 General Guidelines: Action: All exercises should be comfortable and pain-free - no stretching, tingling, or sharp pain. Gently move the foot from side to side in a small arc. Always wear the orthosis when standing or walking. Keep the knees still. It’s normal for the tendon and ankle area to be slightly warmer and Dosage: more swollen than the uninjured side during healing. 3 sets of 20 repetitions However, progressive swelling, redness, or increasing warmth may indicate overuse of the tendon and should be addressed. Exercise 3 Supported seated heel raise in orthosis Foot – Achilles Tendon Program II Position: Home Exercise Program Sahlgrenska University Hospital – Occupational Therapy and Seated, with orthosis on Physiotherapy Deflate the orthosis air cushions and open the front panel Instructions: Hold the top of the orthosis with both hands for support Perform the exercises 3–5 times per day. Action: Perform a small heel lift, keeping the forefoot in contact with the sole. Circulation Do not grip with the toes. 1) Gentle ankle pumps 158 APPENDIX KARI HUSETH 159 This safely activates the calf muscle while the wedges protect the tendon from stretching. Exercise 2 Dosage: Side-to-side ankle movement 2 sets of 10 repetitions Position: Seated or lying face down as in Exercise 1 General Guidelines: Action: All exercises should be comfortable and pain-free - no stretching, tingling, or sharp pain. Gently move the foot from side to side in a small arc. Always wear the orthosis when standing or walking. Keep the knees still. It’s normal for the tendon and ankle area to be slightly warmer and Dosage: more swollen than the uninjured side during healing. 3 sets of 20 repetitions However, progressive swelling, redness, or increasing warmth may indicate overuse of the tendon and should be addressed. Exercise 3 Supported seated heel raise in orthosis Foot – Achilles Tendon Program II Position: Home Exercise Program Sahlgrenska University Hospital – Occupational Therapy and Seated, with orthosis on Physiotherapy Deflate the orthosis air cushions and open the front panel Instructions: Hold the top of the orthosis with both hands for support Perform the exercises 3–5 times per day. Action: Perform a small heel lift, keeping the forefoot in contact with the sole. Circulation Do not grip with the toes. 1) Gentle ankle pumps 158 APPENDIX KARI HUSETH 159 Pump the foot up and down softly. Lift the heels to perform a heel raise. 20 repetitions You may place a roll under the knees for support. Seated foot jogging The movement should be pain-free and comfortable for the tendon. 20 repetitions Perform small alternating bouncing movements with the feet while seated. 20 repetitions Activation Heel raise 2) Foot cupping with relaxed toes Repeat the seated heel raise again. 20 repetitions Gently form a dome shape with the foot while keeping the toes relaxed. 10 repetitions Standing Exercises (with shoes) Mobility Instructions: Perform standing exercises with shoes on. 3) Forward-backward weight shift Keep the entire foot sole in contact with the floor. 5) Lateral weight shifting (side-to-side) Move the knee and body weight forward and backward over the foot. Transfer weight from one leg to the other. On the final repetition, hold the end position for a few seconds. Load the entire foot on the stance leg. 10 repetitions Feel muscle activation, especially in the gluteal region. 10 repetitions Strength 4) Seated heel raise 6) Gait preparation exercise Sit with the entire forefoot on the floor. Stand with a book or rolled towel under both heels and lean against a wall. You may rest your hands on your knees. 160 APPENDIX KARI HUSETH 161 Pump the foot up and down softly. Lift the heels to perform a heel raise. 20 repetitions You may place a roll under the knees for support. Seated foot jogging The movement should be pain-free and comfortable for the tendon. 20 repetitions Perform small alternating bouncing movements with the feet while seated. 20 repetitions Activation Heel raise 2) Foot cupping with relaxed toes Repeat the seated heel raise again. 20 repetitions Gently form a dome shape with the foot while keeping the toes relaxed. 10 repetitions Standing Exercises (with shoes) Mobility Instructions: Perform standing exercises with shoes on. 3) Forward-backward weight shift Keep the entire foot sole in contact with the floor. 5) Lateral weight shifting (side-to-side) Move the knee and body weight forward and backward over the foot. Transfer weight from one leg to the other. On the final repetition, hold the end position for a few seconds. Load the entire foot on the stance leg. 10 repetitions Feel muscle activation, especially in the gluteal region. 10 repetitions Strength 4) Seated heel raise 6) Gait preparation exercise Sit with the entire forefoot on the floor. Stand with a book or rolled towel under both heels and lean against a wall. You may rest your hands on your knees. 160 APPENDIX KARI HUSETH 161 Alternate lifting and lowering each heel gently. Elevate the foot while sitting. Focus on stable hips, relaxed toes, and fluid knees. Perform seated ankle pumps and toe spreading and gripping. 20 repetitions If needed, consider using a compression sock. 7) Gait training Walk in a straight line, placing one foot directly in front of the other. Imagine walking on a tightrope. Walk 10 steps forward, then 10 steps backward. Use crutches until you feel stable without them. Walking Guidelines: Aim to walk with a normal gait pattern: heel strike, roll through, and even step length. Short steps are often better in the early phase. Use crutches as long as needed. Walk as much as necessary in daily life, but do not walk for exercise at this stage. Many post-injury issues are caused by  over-walking  during early recovery. To Reduce or Prevent Swelling: 162 APPENDIX KARI HUSETH 163 Alternate lifting and lowering each heel gently. Elevate the foot while sitting. Focus on stable hips, relaxed toes, and fluid knees. Perform seated ankle pumps and toe spreading and gripping. 20 repetitions If needed, consider using a compression sock. 7) Gait training Walk in a straight line, placing one foot directly in front of the other. Imagine walking on a tightrope. Walk 10 steps forward, then 10 steps backward. Use crutches until you feel stable without them. Walking Guidelines: Aim to walk with a normal gait pattern: heel strike, roll through, and even step length. Short steps are often better in the early phase. Use crutches as long as needed. Walk as much as necessary in daily life, but do not walk for exercise at this stage. Many post-injury issues are caused by  over-walking  during early recovery. To Reduce or Prevent Swelling: 162 APPENDIX KARI HUSETH 163