Data for: Mobility of the human foot's medial arch helps enables upright bipedal locomotion

Developing the ability to habitually walk and run upright on two feet is
one of the most significant transformations to have occurred in human
evolution. Many musculoskeletal adaptations enabled bipedal locomotion,
including dramatic structural changes to the foot and, in particular, the
evolution of an elevated medial arch. The foot’s arched structure has
previously been assumed to play a central role in directly propelling the
center of mass forward and upward through leverage about the toes and a
spring-like energy recoil. However, it is unclear whether or how the
plantarflexion mobility and height of the medial arch support its
propulsive lever function. Here we show, using high-speed biplanar x-ray,
that regardless of intraspecific differences in medial arch height, arch
recoil enables a longer contact time and favorable propulsive conditions
at the ankle for walking upright on an extended leg. This mechanism may
have helped drive the evolution of the longitudinal arch after our last
common ancestor with chimpanzees, who lack this plantarflexion mobility
during push-off. We discovered that the generally overlooked
navicular-medial cuneiform joint is primarily responsible for arch recoil
in human arches, suggesting that future morphological investigations of
this joint will provide new interpretations of the fossil record. Our work
further suggests that enabling longitudinal arch recoil in footwear and
surgical interventions may be critical for maintaining the ankle’s natural
propulsive ability.