Adding Stiffness to the Foot Modulates Soleus Force-Velocity Behaviour during Human Walking

Area of Science:

• Biomechanics
• Human Locomotion
• Musculoskeletal System

Background:

• Foot and ankle structures exhibit complex interactions influencing human locomotion.
• Foot structure dictates lever arms, affecting ankle plantar flexor force generation during push-off.
• Foot deformation can dissipate mechanical energy, impacting locomotion efficiency.

Purpose of the Study:

• To investigate the interplay between foot and ankle mechanics during walking.
• To quantify the effects of increased foot stiffness on soleus muscle-tendon dynamics.
• To determine the impact of altered foot mechanics on whole-body metabolic cost.

Main Methods:

• Investigated foot-ankle interplay by increasing foot stiffness using shoes and insoles.
• Utilized in vivo ultrasonography to measure soleus muscle-tendon mechanics during walking.
• Analyzed changes in energy dissipation, gear ratio, muscle force, and fascicle shortening speed.

Main Results:

• Increased foot stiffness significantly decreased energy dissipation (p < 0.001) and increased the gear ratio (p < 0.001).
• Soleus muscle exhibited greater peak force (p < 0.001) and reduced fascicle shortening speed (p < 0.001) with added stiffness.
• Whole-body metabolic cost of walking increased significantly with added foot stiffness (p < 0.001).

Conclusions:

• Added foot stiffness alters muscle-tendon mechanics, shifting towards higher force and slower shortening.
• Increased metabolic cost of walking with added foot stiffness is likely due to compromised plantar flexor mechanical advantage.
• Findings highlight the trade-offs between foot compliance and energetic cost in human locomotion.