What it is
Using three-dimensional marker-based kinematics and ground reaction force data from humans and chimpanzees walking bipedally and quadrupedally, the authors quantified how the two species strike the ground. Chimpanzees used 2.4 to 8.6 times greater ranges of foot-strike angles than humans and often did not heel-strike, and in both species heel-striking was associated with high impact peak forces and loading rates. Humans expended 26 to 41% more metabolic energy when contacting the ground with the distal foot before the heel, pointing to a trade-off in which heel-striking lowers walking cost but raises potentially damaging impact loading rates.
Why it matters
Qualitative similarities between human and African ape heel-strikes have been used to argue about the origins of hominin bipedalism, but the mechanical data were too sparse to characterize the differences or their consequences. By measuring the forces and energy costs directly, this work reframes heel-striking as an adaptive trade-off, suggesting early hominins with primitive lower-limb anatomy faced a choice between high impacts and uneconomical walking that likely constrained their terrestrial mobility.
Underlined numbers link to their source. Every metric and quoted figure is listed under Sources and data below.
Filed underPrimate Behavior and Ecology, Pleistocene-Era Hominins and Archaeology, Robotic Locomotion and Control