1/26/2024 0 Comments Human and chimpanzee feet jointsThe presence of a high medial arch in fossil hominins has been argued to represent an adaptation for both the foot’s levering ability in push-off ( Elftman and Manter, 1935a Susman, 1983 Sarrafian, 1987) and its mobility-enabled spring-like function ( Hicks, 1955 Holowka and Lieberman, 2018 McNutt et al., 2018). Features unique to the human foot, such as a pronounced medial arch, have been proposed to play a key role in the evolution of habitual bipedalism ( Elftman and Manter, 1935b). The foot experienced strong selective pressures during human evolution. Our work further suggests that enabling medial arch recoil in footwear and surgical interventions may be critical for maintaining the ankle’s natural propulsive ability. Future morphological investigations of the navicular-medial cuneiform joint will likely provide new interpretations of the fossil record. The mechanism through which arch recoil enables an upright ankle posture may have helped drive the evolution of the longitudinal arch after our last common ancestor with chimpanzees, who lack arch plantarflexion mobility during push-off. The generally overlooked navicular-medial cuneiform joint is primarily responsible for arch recoil in human arches. We show 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. We use high-speed biplanar x-ray measurements of foot bone motion on seven participants while walking and running and compare their motion to a subject-specific model without arch recoil. However, it is unclear whether or how the plantarflexion mobility and height of the medial arch support its propulsive lever function. 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. Many musculoskeletal adaptations enabled bipedal locomotion, including dramatic structural changes to the foot and, in particular, the evolution of an elevated medial arch.
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