Foot-stiffening socks reduce the metabolic cost of walking.

Custom foot-stiffening socks applied more forefoot pressure than commercially available socks.

• The abstract reports greater pressure on the user's forefoot with the custom socks (p < 0.001).
• The socks were custom made to stiffen the foot, and commercial socks served as the control condition.

Foot-stiffening socks increased medial longitudinal arch stiffness through cross-axis coupling.

• The increase in arch stiffness was statistically significant (p = 0.034).
• The abstract attributes the effect to forefoot pressure acting on arch stiffness via cross-axis coupling.

Walking with foot-stiffening socks reduced whole-body metabolic rate by about 2% compared with commercial socks.

• The reported significance was p = 0.008.
• The comparison was between foot-stiffening socks and commercially available socks in human walking.

Stiffening the feet increased ankle gear ratio during walking.

• Peak ankle gear ratio increased (p = 0.017).
• Average ankle gear ratio increased (p = 0.045).

Stiffening the feet reduced the ankle's average angular velocity during stance phase.

• The reduction in average ankle angular velocity during stance was significant (p = 0.018).

Leg muscle fascicle shortening velocities decreased by 15-20% with foot-stiffening socks.

• Soleus fascicle shortening velocity decreased (p = 0.023).
• Medial gastrocnemius fascicle shortening velocity decreased (p = 0.005).

Estimated leg active muscle volume was reduced by 9-12%, significantly in one of two models.

• Model 1 showed a significant reduction (p = 0.015).
• Model 2 did not reach significance (p = 0.142).
• The reduced shortening velocities are described as contributing to the lower estimated active muscle volume.

The authors conclude that foot-stiffening socks make walking less effortful by eliciting more economical leg muscle contractions, supporting the theory that evolved foot stiffening aids bipedal locomotion.

• The study tested a theory that greater foot longitudinal bending stiffness reduces whole-body metabolic rate, for which empirical evidence had been elusive.
• The mechanism proposed is higher ankle gear ratio, lower ankle angular velocity, slower muscle shortening, and lower active muscle volume.