Leg Muscle Architecture in Primates and Its Correlation with Locomotion Patterns

Area of Science:

• Primate anatomy and biomechanics
• Paleoanthropology
• Functional morphology

Background:

• Leg bone structure in primates correlates with locomotion.
• Understanding muscle architecture complements skeletal analysis for inferring primate behavior.
• Extinct primate locomotion is often reconstructed using osteological correlates.

Purpose of the Study:

• To investigate if leg muscle architecture patterns mirror those found in primate leg bone structure.
• To analyze muscle mass, fascicle lengths (FL), physiological cross-sectional area (PCSA), reduced PCSA (RPCSA), and tendon-to-muscle belly ratio across diverse primate species.
• To identify phylogenetic and functional signals within primate leg muscle architecture.

Main Methods:

• Studied muscle variables in 33 primate species (strepsirrhines, platyrrhines, catarrhines).
• Grouped muscles into toe and ankle flexors and extensors.
• Analyzed scaling relationships with body mass and compared muscle-tendon unit ratios between leaping and non-leaping primates.

Main Results:

• All studied muscle variables strongly correlate with body mass; strength variables (mass, PCSA, RPCSA) show positive allometry.
• Speed/stretch measure (FL) trends toward negative allometry, indicating relatively shorter muscle fibers in larger primates.
• Leaping primates have a significantly smaller plantarflexor belly-muscle tendon unit (MTU) length ratio.

Conclusions:

• Primate leg muscle architecture is complex and related to body mass and specific locomotor behaviors like leaping.
• While no significant correlations were found between muscle architecture and substrate/locomotor groups overall, trends suggest potential for future research with larger samples.
• Further studies are needed to fully elucidate the relationship between leg bone biomechanics and muscle architecture in primates.