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. 2017 Jul 11;114(28):7343-7348.
doi: 10.1073/pnas.1619071114. Epub 2017 Jun 26.

Chimpanzee super strength and human skeletal muscle evolution

Matthew C O'Neill  1 , Brian R Umberger  2 , Nicholas B Holowka  3 , Susan G Larson  4 , Peter J Reiser  5
Affiliations

Chimpanzee super strength and human skeletal muscle evolution

Matthew C O'Neill et al. Proc Natl Acad Sci U S A. .

Abstract

Since at least the 1920s, it has been reported that common chimpanzees (Pan troglodytes) 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.

Keywords: chimpanzee; human; muscle; muscle modeling; myosin heavy chain.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Muscle contractile properties. (A) Chimpanzee single fibers were sampled from m. vastus lateralis (VL) and m. gastrocnemius lateralis (GL). Insets show a chimpanzee single muscle fiber as well as the identification of the fiber MHC isoform content using gel electrophoresis after Po and Vo measurements. (B) The main effect of MHC isoform content on single-fiber Po; n = 55; error bars, SD; P value is the result of an ANOVA; F(2,52) = 21.20. Paired comparisons indicate that the MHC I (n = 31), IIa (n = 15), and IId (n = 9) Po samples all differ significantly from each other (P < 0.05, Tukey’s honest significant difference tests). (C) The main effect of MHC isoform content on single-fiber Vo; n = 22; error bars, SD; P value is the result of an ANOVA; F(2,19) = 97.16. Paired comparisons indicated that the MHC I (n = 14), IIa (n = 7), and IId (n = 1 estimate, SI Appendix, SI Methods) Vo samples all differed significantly from each other (P < 0.05, one-sample t tests). (D and E) The mean Po and Vo of chimpanzee (stars) muscle compared with human (circles) muscle; P values are the results of one-sample t tests. (F and G) The size scaling of Po and Vo across mammals ranging in mass from 0.01 kg (mouse) to 2,500 kg (rhino) for MHC I, IIa, and IId. Dashed lines are pGLS regression lines of Po and Vo against body mass by MHC isoform.
Fig. 2.
Fig. 2.
MHC isoform distributions and average fiber length of chimpanzee and human skeletal muscles. (A) Chimpanzees exhibit a balanced distribution of the three MHC isoforms across 35 skeletal muscles (SI Appendix, Table S3). P value is the result of an ANOVA [F(2,111) = 1.339, P = 0.197]. (B) For the same muscles, humans exhibit a significant bias toward slow-twitch fibers in their skeletal muscle with measurements ranging from (i) 69.2 ± 11.7% (14) [t(72) = 14.04, P < 0.0001, t test] to (ii) 52.6 ± 7.9% (15) [t(73) = 9.29, P < 0.0001, t test]. This is in contrast to 31.5 ± 11.4% in chimpanzees. (C) Chimpanzee muscle fibers also constitute a greater percentage of their total muscle–tendon unit length than do human muscle fibers (i.e., [Lo/(Lo + Ls)]⋅100, C: 59.0 ± 0.21; H: 44.0 ± 0.25) (23, 24) [t(84) = 2.87, P = 0.0052, t test].
Fig. 3.
Fig. 3.
Muscle model simulations. Single-burst maximal accelerations of an inertial load (first column) and controlled cyclical contractions (second and third columns) were simulated with our chimpanzee muscle and human muscle models. The design of each simulation apparatus is shown at the column top in schematic form with a muscle model affixed in situ. Dashed line is optimal fiber length (Lo). The chimpanzee muscle model generated higher maximum dynamic force and power outputs than the human muscle model under matched simulation conditions.
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References

    1. Doran DM. Comparative locomotor behavior of chimpanzees and bonobos: The influence of morphology on locomotion. Am J Phys Anthropol. 1993;91:83–98. - PubMed
    1. Susman RL, Stern JT., Jr Functional morphology of Homo habilis. Science. 1982;217:931–934. - PubMed
    1. Ruff CB, Trinkaus E, Holliday TW. Body mass and encephalization in Pleistocene Homo. Nature. 1997;387:173–176. - PubMed
    1. Shea JJ. The origins of lithic projectile point technology: Evidence from Africa, the Levant, and Europe. J Archaeol Sci. 2006;33:823–846.
    1. Marlowe FW. Hunter-gatherers and human evolution. Evol Anthropol. 2005;14:54–67. - PubMed

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