Step width and frontal plane trunk motion in bipedal chimpanzee and human walking

Area of Science:

• Anthropology
• Biomechanics
• Paleoanthropology

Background:

• Human bipedalism involves mediolateral oscillations of the center of mass (CoM) between the feet.
• Understanding frontal plane control strategies in human bipedalism is limited by data from ape facultative bipedalism.

Purpose of the Study:

• To investigate the relationship between step width, mediolateral CoM motion, trunk kinematics, and CoM power during bipedalism in humans and chimpanzees.
• To determine if human frontal plane control strategies are unique.

Main Methods:

• Collected three-dimensional kinematic and kinetic data in humans and chimpanzees during bipedalism.
• Analyzed step width, mediolateral CoM motion, frontal plane trunk kinematics, and CoM power.
• Developed a method to estimate mediolateral CoM motion from trackway step width.

Main Results:

• Chimpanzee bipedalism involves wider steps and larger mediolateral CoM oscillations compared to humans.
• Chimpanzees exhibit significant trunk motion, listing over the stance leg, while humans show minimal trunk angular motion.
• Narrow mediolateral CoM motions are unique to humans, attributed to adducted hips and valgus knees.

Conclusions:

• Human frontal plane control, characterized by narrow CoM motions, is distinct from that of chimpanzees and other primates.
• Valgus knees, present early in the human fossil record, likely contribute to human bipedal gait efficiency.
• Early hominins like Ardipithecus ramidus may have exhibited wider steps and larger CoM/trunk motions, preceding the evolution of significant knee valgus.