Comparative analysis of muscle architecture in primate arm and forearm

A comparative study of myological morphology, i.e. muscle mass (MM), muscle fascicle length and muscle physiological cross-sectional area (an indicator of the force capacity of muscles), was conducted in nine primate species: human (Homo sapiens), chimpanzee (Pan troglodytes), gibbon (Hylobates spp.), papio (Papio hamadryas), lutong (Trachypithecus francoisi), green monkey (Chlorocebus aethiops), macaque monkey (Macaca spp.), capuchin monkey (Cebus albifrons) and squirrel monkey (Saimiri sciureus). The MM distributions and the percentages in terms of functional categories were calculated as the ratios of the muscle masses. Moreover, individual normalized data were compared directly amongst species, independent of size differences. The results show that the different ratios of forearm-rotation muscles between chimpanzee and gibbons may be related to the differences in their main positional behaviour, i.e. knuckle-walking in chimpanzees and brachiation in gibbons, and the different frequencies of arm-raising locomotion between these two species. Moreover, monkeys have larger normalized MM values for the elbow extensor muscles than apes, which may be attributed to the fact that almost all monkeys engage in quadrupedal locomotion. The characteristics of the muscle internal parameters of ape and human are discussed in comparison with those of monkey.