Functional adaptations of primate forearm and leg muscle fiber architecture

has been correlated with locomotion, posture and substrate use in primates, but less attention has been paid to myological adaptations. Previously we presented data on the functional correlates of primate forearm muscle fiber architecture variables: fascicle length (FL), physiological cross-sectional area (PCSA) and reduced PCSA (RPCSA). Here, we greatly expand thesample to include 9 strepsirrhine, 15 platyrrhine, and 20 catarrhine taxa spanning the entire size range of the order (Microcebus to Gorilla), and we also include fiber data from the leg. Forearm muscle mass scales with positive allometry across all primates. Catarrhines exhibit positive allometry in their PCSA and RPCSA indicating that larger catarrhines have relatively stronger forearm muscles. While PCSA and RPCSA scale with isometry for terrestrial species, they scale with positive allometry for arboreal ones – thus larger arboreal primates have relatively stronger forearms. Surprisingly, there are no differences in the forearm architecture of quadrupeds (QUAD) when compared to vertical clinging and leaping/suspensory species (VCL). All leg strength variables (mass, PCSA, RPCSA) scale with positive allometry, and speed/stretch measure (FL) scales with isometry across the sample. Thus, larger primates are relatively stronger though not more flexible/faster. There is no other phylogenetic signal in the leg muscles. Arboreal primates have greater leg RPCSA and QUAD have statistically heavier leg muscles than VCL, though they are not greater in cross-sectional area or reduced in FL.