title: Human soleus sarcomere lengths measured using in vivo microendoscopy at two ankle flexion angles.
abstract: The forces generated by the soleus muscle play an important role in standing and locomotion. The lengths of the sarcomeres of the soleus affect its force-generating capacity, yet it is unknown how sarcomere lengths in the soleus change as a function of ankle flexion angle. In this study, we used microendoscopy to measure resting sarcomere lengths at 10° plantarflexion and 20° dorsiflexion in 7 healthy individuals. Mean sarcomere lengths at 10° plantarflexion were 2.84±0.09µm (mean±S.E.M.), near the optimal length for sarcomere force generation. Sarcomere lengths were 3.43±0.09µm at 20° dorsiflexion, indicating that they were longer than optimal length when the ankle was in dorsiflexion and the muscle was inactive. Our results indicate a smaller sarcomere length difference between two ankle flexion angles compared to estimates from musculoskeletal models and suggest why these models frequently underestimate the force-generating capacity of the soleus.
authors.affiliation: Department of Mechanical Engineering, Stanford University, United States.
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Mechanical Engineering, Stanford University, United States; Department of Bioengineering, Stanford University, United States. Electronic address: delp@stanford.edu.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Delp
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology; D004724:Endoscopy / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology / Q000648:ultrastructure*; D011187:Posture; D016059:Range of Motion, Articular; D012518:Sarcomeres / Q000502:physiology / Q000648:ultrastructure*; D055815:Young Adult
keywords: Ankle; In vivo imaging; Muscle; Sarcomere; Soleus