The initiation of a walking step with a heel strike is a defining characteristic of humans and great apes but is rarely found in other mammals. Despite the considerable importance of heel strike to an understanding of human locomotor evolution, no one has explicitly tested the fundamental mechanical question of why great apes use a heel strike. In this report, we test two hypotheses (1) that heel strike is a function of hip protraction and/or knee extension and (2) that short-legged apes with a midfoot that dorsiflexes at heel lift and long digits for whom digitigrady is not an option use heel-strike plantigrady. This strategy increases hip translation while potentially moderating the cost of redirecting the center of mass (‘collisional costs’) during stance via rollover along the full foot from the heel to toes. We quantified hind limb kinematics and relative hip translation in ten species of primates, including lemurs, terrestrial and arboreal monkeys, chimpanzees, and gorillas. Chimpanzees and gorillas walked with relatively extended knees but only with moderately protracted hips or hind limbs, partially rejecting the first hypothesis. Nonetheless, chimpanzees attained relative hip translations comparable with those of digitigrade primates. Heel-strike plantigrady may be a natural result of a need for increased hip translations when forelimbs are relatively long and digitigrady is morphologically restricted. In addition, foot rollover from the heel to toe in large, short-legged apes may reduce energetic costs of redirecting the center of mass at the step-to-step transition as it appears to do in humans. Heel strike appears to have been an important mechanism for increasing hip translation, and possibly reducing energetic costs, in early hominins and was fundamental to the evolution of the modern human foot and human bipedalism.

脚后跟走路开始步行是人类和大猿的定义特征，但在其他哺乳动物中很少见。尽管脚跟撞击对于理解人类运动进化具有相当重要的意义，但没有人明确测试过为什么大猿类会使用脚跟撞击的基本机械问题。在本报告中，我们检验了两个假设（1）脚跟前移是髋关节前伸和/或膝盖伸展的函数，（2）短脚猿人的中足在脚后跟抬起时背屈，而长指没有这个数字一种选择是使用后跟打击植物。这种策略增加了髋关节的平移度，同时有可能减轻姿态期间通过沿着整个脚从脚跟到脚趾的翻转而改变重心的成本（“碰撞成本”）。我们对十种灵长类动物的后肢运动学和相对髋翻译进行了量化，包括狐猴，陆地和树栖猴子，黑猩猩和大猩猩。黑猩猩和大猩猩的膝盖相对伸展，但臀部或后肢的伸展程度适中，部分拒绝了第一种假设。尽管如此，黑猩猩的相对髋部翻译水平可与数位灵长类灵长类动物相比。当前肢相对较长且在形态上受数字指限时，足跟下垂可能是需要增加髋关节平移的自然结果。另外，在大型短腿猿中，脚跟从脚跟到脚趾的翻滚可能会减少步步过渡时重心转移的精力，这在人体中似乎很常见。