title: Adding Stiffness to the Foot Modulates Soleus Force-Velocity Behaviour during Human Walking.
abstract: Previous studies of human locomotion indicate that foot and ankle structures can interact in complex ways. The structure of the foot defines the input and output lever arms that influences the force-generating capacity of the ankle plantar flexors during push-off. At the same time, deformation of the foot may dissipate some of the mechanical energy generated by the plantar flexors during push-off. We investigated this foot-ankle interplay during walking by adding stiffness to the foot through shoes and insoles, and characterized the resulting changes in in vivo soleus muscle-tendon mechanics using ultrasonography. Added stiffness decreased energy dissipation at the foot (p < 0.001) and increased the gear ratio (i.e., ratio of ground reaction force and plantar flexor muscle lever arms) (p < 0.001). Added foot stiffness also altered soleus muscle behaviour, leading to greater peak force (p < 0.001) and reduced fascicle shortening speed (p < 0.001). Despite this shift in force-velocity behaviour, the whole-body metabolic cost during walking increased with added foot stiffness (p < 0.001). This increased metabolic cost is likely due to the added force demand on the plantar flexors, as walking on a more rigid foot/shoe surface compromises the plantar flexors' mechanical advantage.
authors.affiliation: Department of Biomechanics, University of Nebraska at Omaha, USA.
authors.forename: Kota Z
authors.initials: KZ
authors.lastname: Takahashi
authors.affiliation: Division of Physical Therapy, University of North Carolina at Chapel Hill, USA.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Gross
authors.affiliation: Department of Health and Exercise Science, Appalachian State University, USA.
authors.forename: Herman
authors.initials: H
authors.lastname: van Werkhoven
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, USA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Piazza
authors.affiliation: Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University, USA.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Sawicki
mesh_terms: D000842:Ankle / Q000502:physiology; D001696:Biomechanical Phenomena / Q000502:physiology*; D005528:Foot / Q000502:physiology*; D005684:Gait / Q000502:physiology; D006801:Humans; D018482:Muscle, Skeletal / Q000502:physiology*; D016138:Walking / Q000502:physiology*