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Gearing Up the Human Ankle-Foot System to Reduce Energy Cost of Fast Walking

During locomotion, the human ankle-foot system dynamically alters its gearing, or leverage of the ankle joint on the ground. Shifting ankle-foot gearing regulates speed of plantarflexor (i.e., calf muscle) contraction, which influences economy of force production. Here, we tested the hypothesis that...

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Detalles Bibliográficos
Autores principales: Ray, Samuel F., Takahashi, Kota Z.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Nature Publishing Group UK 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7260196/
https://www.ncbi.nlm.nih.gov/pubmed/32472010
http://dx.doi.org/10.1038/s41598-020-65626-5
Descripción
Sumario:During locomotion, the human ankle-foot system dynamically alters its gearing, or leverage of the ankle joint on the ground. Shifting ankle-foot gearing regulates speed of plantarflexor (i.e., calf muscle) contraction, which influences economy of force production. Here, we tested the hypothesis that manipulating ankle-foot gearing via stiff-insoled shoes will change the force-velocity operation of plantarflexor muscles and influence whole-body energy cost differently across walking speeds. We used in vivo ultrasound imaging to analyze fascicle contraction mechanics and whole-body energy expenditure across three walking speeds (1.25, 1.75, and 2.0 m/s) and three levels of foot stiffness. Stiff insoles increased leverage of the foot upon the ground  (p < 0.001), and increased dorsiflexion range-of-motion (p < 0.001). Furthermore, stiff insoles resulted in a 15.9% increase in average force output (p < 0.001) and 19.3% slower fascicle contraction speed (p = 0.002) of the major plantarflexor (Soleus) muscle, indicating a shift in its force-velocity operating region. Metabolically, the stiffest insoles increased energy cost by 9.6% at a typical walking speed (1.25 m/s, p = 0.026), but reduced energy cost by 7.1% at a fast speed (2.0 m/s, p = 0.040). Stiff insoles appear to add an extra gear unavailable to the human foot, which can enhance muscular performance in a specific locomotion task.