title: Comparison of human gastrocnemius forces predicted by Hill-type muscle models and estimated from ultrasound images.
abstract: Hill-type models are ubiquitous in the field of biomechanics, providing estimates of a muscle's force as a function of its activation state and its assumed force-length and force-velocity properties. However, despite their routine use, the accuracy with which Hill-type models predict the forces generated by muscles during submaximal, dynamic tasks remains largely unknown. This study compared human gastrocnemius forces predicted by Hill-type models with the forces estimated from ultrasound-based measures of tendon length changes and stiffness during cycling, over a range of loads and cadences. We tested both a traditional model, with one contractile element, and a differential model, with two contractile elements that accounted for independent contributions of slow and fast muscle fibres. Both models were driven by subject-specific, ultrasound-based measures of fascicle lengths, velocities and pennation angles and by activation patterns of slow and fast muscle fibres derived from surface electromyographic recordings. The models predicted, on average, 54% of the time-varying gastrocnemius forces estimated from the ultrasound-based methods. However, differences between predicted and estimated forces were smaller under low speed-high activation conditions, with models able to predict nearly 80% of the gastrocnemius force over a complete pedal cycle. Additionally, the predictions from the Hill-type muscle models tested here showed that a similar pattern of force production could be achieved for most conditions with and without accounting for the independent contributions of different muscle fibre types.
authors.affiliation: Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada V5A 1S6 taylor_dick@sfu.ca.
authors.forename: Taylor J M
authors.identifier: 0000-0001-8371-6247
authors.initials: TJM
authors.lastname: Dick
authors.affiliation: Concord Field Station, Harvard University, Bedford, MA 01730, USA.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Biewener
authors.affiliation: Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada V5A 1S6.
authors.forename: James M
authors.initials: JM
authors.lastname: Wakeling
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D014463:Ultrasonography
keywords: B-mode ultrasound; Electromyography; Motor unit recruitment; Musculoskeletal simulation