Duke University, Durham, NC, 27708-0383, USA.
Duke University, Durham, NC, 27708-0383, USA.
J Hum Evol. 2020 Aug;145:102840. doi: 10.1016/j.jhevol.2020.102840. Epub 2020 Jul 8.
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.
跟踺先着地的行走起始方式是人类和大猿类的特征，但在其他哺乳动物中很少见。尽管跟踺着地对理解人类运动进化具有重要意义，但没有人明确测试过大猿类使用跟踺着地的基本机械问题。在本报告中，我们测试了两个假设：（1）跟踺着地是髋关节前伸和/或膝关节伸展的功能；（2）中足背屈、跗跖关节跖屈、长趾且不能趾行的短肢猿类，使用跟踺着地的跖行方式。这种策略增加了髋关节的平移，同时通过整个足部从跟部到趾部的滚动，潜在地降低了在站立阶段重新引导质心的成本（“碰撞成本”）。我们在 10 种灵长类动物（包括狐猴、地栖和树栖猴、黑猩猩和大猩猩）中定量了后肢运动学和相对髋关节平移。黑猩猩和大猩猩行走时膝关节相对伸展，但髋关节或后肢只有适度前伸，部分否定了第一个假设。尽管如此，黑猩猩的相对髋关节平移与趾行灵长类动物相当。跟踺着地跖行可能是当前肢相对较长且趾行在形态上受到限制时，需要增加髋关节平移的自然结果。此外，在大型短肢猿类中，足部从跟部到趾部的滚动可能会降低在步幅转换过程中重新引导质心的能量成本，这似乎在人类中也是如此。跟踺着地似乎是增加髋关节平移并可能降低能量成本的重要机制，它是人类祖先进化和现代人足和人类双足行走的基础。
