Meeting Abstract
Humans and great apes are the only primates known to make initial substrate contact with the heel of the foot during walking. This ‘heel strike’ foot posture causes high impact peak forces in humans, and some argue that hominins evolved a calcaneus that is more robust than that of great apes to help resist the shock of impact during bipedal walking. However, these forces have not been thoroughly investigated in great apes. We measured impact peak forces at foot strike in three subadult male chimpanzees (avg: 6.1 yrs., 30.9 kg) during bipedal and quadrupedal walking on a flat runway. We found that unlike humans, chimpanzees often make initial contact with the forefoot and midfoot regions instead of the heel during walking, but that foot strike posture does not influence impact peak magnitude (P=0.1). The impact peaks produced by chimpanzees during bipedal walking (0.61±0.11 BW [body weights]) were similar to those previously reported for humans (0.69±0.1 BW; Lafortune and Hennig, 1992). However, chimpanzees incurred much lower impact peaks when walking quadrupedally (0.37±0.17 BW), and produced no impact peak in 23% of the quadrupedal steps we measured. These results suggest that in adopting habitual bipedalism, early hominins would have had to adjust to high impact forces. Although modern humans are capable of avoiding impact peaks during running by switching from heel to forefoot striking, our results suggest that adjusting foot strike posture may not have helped early hominins reduce impact forces during walking. Therefore, hominins may have needed to evolve anatomical specializations to withstand the shock associated with foot strike. Supported by NSF 0935321.
