Analyzing pace frequencies in bipedal primates and primate "predecessors" reveals mechanisms that regulate foot inversion and thus ensure foot stability at touchdown

Abstract

In walking bipedally, various arboreal New World primate species use a “forefoot first” strategy, after which heel contact occurs. A similar walking scenario is seen in arboreal New World marsupials like the opossum, a quadrupedal primate “predecessor”. In opossum walking the swing phase ends with the foot in the inverted position to the next touchdown with the forefoot. We therefore hypothesized that those quadrupedal marsupials which are mainly or exclusively terrestrial like e.g., wombats, will also display a “forefoot first” strategy at touchdown. Our observations reveal that marsupials such as wombats, though being exclusively quadrupedal and non-arboreal, show basically the same strategies of foot eversion to ensure safe touchdown as bipedally walking arboreal New World primate species, with morphologically guided adjustments. Analyzing this hopefully helps to understand gait training problems in patients too, with emphasis on foot inversion and eversion.