School of Anthropology, University of Arizona
Thursday All day, Clinch Concourse
Human bipedal walking is characterized by a habitual “heel-strike plantigrade” gait. However, the significance of foot posture during walking is not as well understood. Studies suggest employing a heel-strike when running may lead to injury due to the magnitude of impact transient forces upon initial contact and running with a mid-foot strike reduces these forces without significantly increasing the cost of transport. This work leaves open the questions of 1) do mid-foot strikes produce similar kinetic advantages during walking, and if so, 2) why should humans’ heel-strike at any speed? In this study, we use kinematic and kinetic data to examine the energetic advantages a plantigrade gait confers during bipedal walking. Subjects (n=11) walked at self-selected speeds using both a heel-strike and mid-foot gait, and we compared walking speed, walk-to-run transition speed, the estimated costs of locomotion (lower limb muscle volume activated during walking), and impact transient forces. Compared to normal heel-strike gaits, mid-foot gaits decreased impact transient (p<0.001), but increased active muscle volume (p=0.0099), decreased walking speed (p=0.0478), and reduced walk-to-run transition speed (p=0.016). Thus, in walking, as opposed to running, mid-foot strikes offer the advantage of a reduced impact transient but compromise with an increased energy cost and a slower walk-to-run transition speed. These trade-offs may be a key to understanding the functional benefits of heel-strike during walking. Given debates over the locomotor mechanics of early hominins, this study contributes new data to our understanding of the adaptive advantages of a striding bipedal gait during human evolution.