Fig. 3. Illustration of the walking postures (at heel-strike, midstance and toe-off) and vertical ground reaction forces (expressed as % body weight) in a human (A) and a chimpanzee (B). The chimpanzee uses a more flexed hip and knee posture throughout stance phase, has lower oscillations of the center of mass, and generates a flatter, lower vertical peak force curve. Human and chimpanzee redrawn from Elftman (1944); force traces re-drawn from Kimura et al. (1979).