Functional Differences in Muscle Architecture Across the Pelvis and Hind Limb of Primates.

OBJECTIVES: Understanding the architectural diversity of primate musculature is essential for interpreting locomotor function and reconstructing evolutionary adaptations. This study examines whether interspecific differences in pelvic and hind limb muscle architecture reflect functional differentiation among major muscle groups.

MATERIALS AND METHODS: We present detailed dissection data from six primate species, alongside a large sample of additional specimens collected from previous studies. We quantify fascicle length, pennation angle, muscle mass, and physiological cross-sectional area across the hind limb and pelvis in each species. We assessed whether differences in muscle architecture were consistent across functional groups and taxa. Differences in muscle architecture were analyzed across functional groups, muscles, and species, with architectural specialization interpreted in functional terms, e.g., reflecting relative emphasis on force, power, displacement, or generalist/stabilizing roles.

RESULTS: Our results reveal conserved configurations in load-bearing muscles, but marked divergence in others, particularly in knee and hip musculature. Notably, muscle specialization was more conserved between species with similarity in their ecology/locomotor mode than between those who are closely related, indicating that muscle architecture is closely linked to habitual hind limb function.

DISCUSSION: These findings suggest that patterns of pelvic and hind limb muscle specialization across primates are driven primarily by ecological and locomotor function, rather than evolutionary relatedness. The dataset provides a detailed, anatomically grounded resource for future comparative and biomechanical studies of primate hind limb function.