Abstract
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.