The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Ontogeny of bipedalism: Changes in the location and direction of the ground reaction force in toddlers


Department of Anthropology, University of Texas at Austin

Saturday 4:15-4:30, Ballroom C Add to calendar

Paleoanthropologists rely on form-function relationships to reconstruct locomotion in fossils. But testing such relationships is challenging. Since juvenile trabeculae are highly responsive to functional loading, an ontogenetic study is an excellent natural experiment with which to test form-function relationships and detect functional loading signals within bones. A pattern of pedal loading from heel-strike to hallucal propulsion is a distinct feature of mature human bipedalism that develops gradually. This study tested the hypothesis that previously reported changes in trabecular architecture reflect changes in the location and direction of the ground reaction force resultant (GRFr) throughout early locomotor development. 3D kinematic and force data were collected on a mixed-longitudinal sample of 20 toddlers, representing the first three years of locomotor independence, and used to calculate the position and direction of the GRFr relative to bony landmarks of the foot.

At the onset of independent walking, the GRFr projects vertically through the distal calcaneus at touchdown. By the end of the first year of walking, the GRFr has shifted and projects posteriorly through the proximal calcaneus at heel-strike. In new walkers, the GRFr is located proximal to the second and third metatarsal heads at lift-off, projecting slightly anteriorly. Hallucal propulsion is present by the end of the first year of walking. Results are consistent with pedal trabecular architecture indicating that prior to two years, toddlers lack internal morphology associated with a powerful toe-off. These data elucidate relationships that can be used to interpret foot function and the development of bipedalism in early hominins.

This study was funded by the Leakey Foundation and NSF (BCS 1028958).

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