Chimpanzee hind limb muscle electromyographic activity patterns during locomotion

Functional interpretation of fossils documenting our early locomotor evolution relies on biomechanical analyses of modern humans and comparative samples of nonhuman primates. Force plate studies have explored the forces that nonhuman primate limbs exchange with the ground while walking bipedally or quadrupedally, and kinematic studies have detailed limb and joint motion profiles during various forms of locomotion. Much less is known about patterns of hind limb muscle use as revealed through electromyography despite the fact that the interpretation of many features of fossils has been related to aspects of muscle use. To better understand how muscle function may relate to the interpretation of fossil material, the current study focuses on chimpanzees and presents electromyography-based activity profiles for the majority of their hind limb muscles during knuckle-walking, bipedalism, and vertical climbing. Taking advantage of the long history of the Stony Brook Primate Locomotion Lab, this study has compiled electromyographic data from eight chimpanzee subjects to both document hind limb muscle activity patterns and explore variability in those recruitment profiles. The collected data indicate that while there are many commonalities in patterns of muscle use, there is also a fair amount of intersubject variation. Overall, the locomotor adaptive strategy of chimpanzees appears to emphasize versatility and maneuverability rather than energy-efficient locomotion. It is hoped that these data will broaden perspectives on how patterns of muscle use may influence the interpretation of fossils.