Chimpanzee super strength and human skeletal muscle evolution

Significance Chimpanzee “super strength” has been widely reported since the 1920s although a critical review of the available data suggests that the chimpanzee–human muscular performance differential is only ∼1.5 times. Some hypothesize that this differential reflects underlying differences in muscle mechanics. Here, we present direct measurements of chimpanzee skeletal muscle properties in comparison with those of humans and other terrestrial mammals. Our results show that chimpanzee muscle exceeds human muscle in maximum dynamic force and power output by ∼1.35 times. This is primarily due to the chimpanzee’s higher fast-twitch fiber content, rather than exceptional maximum isometric force or maximum shortening velocities. We suggest that muscular performance capabilities declined during hominin evolution in response to selection for repetitive, low-cost contractile behavior.