The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

GRF moment arms about the knee in A.L. 288-1


1Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, 2Department of Biology, University of Antwerp, 3Departments of Anthropology and Orthopaedics and Sports Medicine, University of Washington

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Although it is generally agreed that australopiths were bipeds, some researchers project bipedal modernity into the early hominin fossil record, while others argue that australopiths utilized a ‘bent-hip, bent-knee’ form of bipedalism. Here we model potential midstance positions using human and chimpanzee kinematics as boundary conditions and combine those with human and chimpanzee body segment parameters to calculate the ground reaction force (GRF) moment arms about the knee for A.L.288-1 and an average modern human female.

Midstance lower limb joint angles and body segment parameters for chimpanzees and modern humans were derived from the literature. 248,216 potential midstance positions were created using combinations of joint angles (one degree increments between boundary conditions) and segment parameters then were used to calculate total center of mass. Midstance positions were eliminated if they did not meet two criteria: 1. Total center of mass located above the foot. 2. Angle of trunk within the range of human and chimpanzee (bipedal) walking. The moment arm of the GRF about the knee was then calculated.

We found that a small percentage (~6%) of all potential midstance positions met our retention conditions. Joint angles that produced viable midstance positions were tightly clustered within the total range of kinematic possibilities and these positions were similar for the modern human female and A.L. 288-1. The total range of GRF moment arms about the knee was absolutely larger for the human (28 cm) than for A.L. 288-1 (20 cm), but were a similar percentage of lower limb length in both.

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