Collaborative Research: The Effects of Musculoskeletal Design on Bipedal Walking and Running Performance in Humans, Chimpanzees and Early Hominims

This research examines how musculoskeletal design influences bipedal walking mechanics and energetic requirements in humans and bipedal chimpanzees, with implications for understanding early hominin locomotion. The study directly compares three-dimensional ground reaction forces and lower/hindlimb joint mechanics over a full stride in humans and chimpanzees walking bipedally, assessed at matched dimensionless and dimensional velocities. The investigators tested explicit hypotheses addressing whether humans exhibit lower limb joint work and power during stance—particularly the single-support period—lower work and power for limb swing, and lower total mechanical power when accounting for storage and release of passive elastic strain energy.

Using detailed biomechanical measurements, the team quantified joint work and power across gait phases: first double-support, single-support, and second double-support (push-off), and also evaluated limb-swing mechanics. The results reveal a complex, phase-specific pattern of interspecific differences. Humans produce significantly less work and power during the first double-support and the single-support periods of stance than bipedal chimpanzees, indicating that much of the mechanical burden of supporting and redirecting the body during mid-stance is reduced in humans. In contrast, humans markedly exceed chimpanzees in work and power during the second double-support period, emphasizing a distinct and powerful push-off phase in human walking. Limb swing in humans requires less work and power than in chimpanzees, although this difference did not reach statistical significance in the present sample.

A central finding is the substantial reduction in estimated total positive 'muscle fiber' work and power in humans relative to bipedal chimpanzees: muscle fiber work and power were estimated to be 46.9% and 35.8% lower, respectively, at matched dimensionless speeds. The authors attribute a portion of these reductions to mechanisms for storing and releasing elastic energy at the human ankle and hip. Such elastic energy return reduces the active muscular work required during walking and contributes to the energetic economy that characterizes human bipedalism.

Beyond energetic differences, the study documents qualitative distinctions in foot strike and balance mechanics: humans display distinct heel-strike mechanics and lateral balance strategies compared to bipedal chimpanzees, and humans appear to dissipate more mechanical energy through soft tissue deformations. Together, these contrasts provide a more comprehensive view of the mechanics and energetics of chimpanzee bipedalism and highlight features of human musculoskeletal design that likely contributed to the evolution of efficient habitual bipedal walking in hominins.

By combining three-dimensional force and joint mechanics data across a full stride, the work clarifies where and how human anatomy and passive elastic mechanisms reduce muscular demands during walking, and how these adaptations differ from the compromises observed in bipedal chimpanzees. The findings inform functional interpretations of fossil morphology and strengthen mechanistic links between musculoskeletal design, locomotor mechanics, and the energetic foundations of hominin evolution.