File:HumanChimpBiomechanics.jpg

A diagram comparing the anatomy that controls locomotion between humans and a chimpanzees.

Original caption: Three semicircular canals (top view), the primary organs for maintaining balance, are situated in the inner ear of mammals. In humans, two of the three (pink) help stabilize the runner’s head.

Differences in human and chimpanzee anatomy highlight the human adaptations for long-distance running. There are fewer muscle connections between the head and the shoulders in the human than in the chimpanzee. The weaker connection enables the head to move independently of the shoulder, which rotates while running. In contrast, humans have more connections between the gluteus maximus muscle in the butt and the hip than chimpanzees do, which keeps the trunk and leg moving together. Both the Achilles tendon of the heel and the tendon of the arch of the foot are much smaller in chimpanzees than they are in humans; in a running person they act like springs, absorbing and releasing energy.

Adapted from: Creator uncredited, found at: UCI Biomechanics, no copyright given.