2010/01/01 by Matthew C. O’Neill, Brian R. Umberger, Nicholas B. Holowka +5 · 1 citation
Earth and Planetary Sciences · Materials Science · Psychology · #Children's Physical and Motor Development #Evolution and Paleontology Studies #Multiferroics and related materials #Primate Behavior and Ecology
paper · pdf · doi:10.1073/pnas.1619071114
openalex publication_date 2010/01/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/06/11
Since at least the 1920s, it has been reported that common chimpanzees (<i>Pan troglodytes</i>) differ from humans in being capable of exceptional feats of "super strength," both in the wild and in captive environments. A mix of anecdotal and more controlled studies provides some support for this view; however, a critical review of available data suggests that chimpanzee mass-specific muscular performance is a more modest 1.5 times greater than humans on average. Hypotheses for the muscular basis of this performance differential have included greater isometric force-generating capabilities, faster maximum shortening velocities, and/or a difference in myosin heavy chain (MHC) isoform content in chimpanzee relative to human skeletal muscle. Here, we show that chimpanzee muscle is similar to human muscle in its single-fiber contractile properties, but exhibits a much higher fraction of MHC II isoforms. Unlike humans, chimpanzee muscle is composed of ∼67% fast-twitch fibers (MHC IIa+IId). Computer simulations of species-specific whole-muscle models indicate that maximum dynamic force and power output is 1.35 times higher in a chimpanzee muscle than a human muscle of similar size. Thus, the superior mass-specific muscular performance of chimpanzees does not stem from differences in isometric force-generating capabilities or maximum shortening velocities-as has long been suggested-but rather is due in part to differences in MHC isoform content and fiber length. We propose that the hominin lineage experienced a decline in maximum dynamic force and power output during the past 7-8 million years in response to selection for repetitive, low-cost contractile behavior.