Wrapping the transverse foot arch improves running economy.

Humans have more curved transverse foot arches than extant apes. Through cross-axis coupling, greater transverse foot arch curvature stiffens the overall foot. Because of the functional implications of evolved human foot arch mechanics, we investigated whether tightly wrapping participant transverse foot arches, which accentuates evolved features of transverse and medial longitudinal foot arches, facilitates bipedal running. Overall, wrapping participant transverse arches accentuated the evolved characteristics of transverse arch height and curvature (both d≥1.04, P<0.001), as well as longitudinal arch height and stiffness (both d≥0.64, P≤0.022). Running with wrapped versus bare transverse arches reduced participant leg muscle activation (d=0.57, P=0.043) and whole-body metabolic power (d=0.66, P=0.018). Mechanistically, running with wrapped versus bare transverse foot arches increased peak ankle gear ratio (d=0.60, P=0.031), enabling the ankles to produce mechanical power (average and peak d≤0.07, P≥0.179) using slower angular velocities (d=0.57, P=0.038). Notably, stiffening the medial longitudinal foot arch did not increase its mechanical energy recycling during running (d=0.03, P=0.914). Therefore, wrapping the transverse foot arch facilitates running by enabling leg muscles to operate more economically. Our findings motivate the notion that the evolved curvature of human transverse foot arches may have been naturally selected to increase overall foot stiffness and facilitate bipedal running.