The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

Balancing the body: frontal plane dynamics during locomotion


1Human Evolutionary Biology, Harvard University, 2Alliance Health Project, University of California, San Francisco

March 26, 2015 2:00, Grand Ballroom E/F/G Add to calendar

Hominin bipedalism creates a unique challenge for balancing the body in the frontal plane during locomotion. Because of the high energetic cost of significant mediolateral displacements of the center of mass and their potential effects on lower extremity injuries, selection to reduce forces in the frontal plane should be high. The shape of the hominin ilia and femoral bicondylar angle are important adaptations for minimizing these forces, yet little is known about the interaction of hip and knee joint mechanics for providing frontal plane stability. Increased thigh adduction angle during stance is predicted to decrease body center of mass displacement and mediolateral ground reaction forces, thus reducing hip and knee abduction moments. To test this model we collected full body kinematics and kinetic data on twenty-three subjects walking and running at preferred, narrow, and wide step widths. As predicted, increased thigh adduction angle decreased mediolateral ground reaction forces and body center of mass displacement in both gaits. However, mediolateral ground reaction force magnitude was weakly correlated with knee and hip moments during locomotion. Instead, knee moments during walking decreased with greater knee valgus, while hip moments were positively correlated with knee abduction moments. During running, both hip and knee moments correlated strongly but independently with shank and thigh adduction angles respectively. These data indicate that mediolateral ground reaction force is less influential then lower-limb kinematics on knee and hip moments during walking and running and the dynamics of each gait have different effects on joint stress.