A Comparison of the Force-Velocity Relationship of Bonobo and Human Muscle Fibers

It has been reported that the muscles of chimpanzees and bonobos have "super strength" and it has been suggested that this is attributable to a larger specific tension and specific power of their muscles. To investigate this we compared the force-velocity relationship in 85 human and 49 bonobo (Pan paniscus) skinned fibers at 15°C. Fibers were classified as type I or II with gel electrophoresis. Type II fibers had a higher maximal shortening velocity (Vmax) and lower curvature of the force-velocity relationship (higher a/Po) than type I fibers in both species (p < 0.001). Although bonobo fibers of both types were larger and produced more force than human fibers, their specific tension and Vmax were lower (p < 0.001). The a/Po was higher in bonobo fibers (p < 0.001). Combined these differences in the parameters of the force-velocity relationship resulted in a similar specific power in bonobo and human fibers. The lesser curvature of the force-velocity relationship offsets the negative effects of a lower specific tension and Vmax on specific power of bonobo muscle fibers. The "super strength" of bonobos cannot be explained by differences in muscle fiber contractile properties but may reflect a higher proportion of type II fibers than in human muscle.