Biomechanics of balance and posture

Considerable complexity underlies even the simplest human movements. For example, to walk across a room, muscles must simultaneously support the weight of the body, maintain balance, and move the limb segments. To improve our understanding of how the motor system controls these tasks, we conduct innovative experiments in our state-of-the-art motion capture studios, and apply engineering tools to analyze the resulting data. A specific focus is on the reflex or "triggered" responses (e.g., stepping and grasping) that are used to recover balance in the event of an impending fall, and how these are influenced by disease and aging.

"Tether release" experiments allow us to tease out the importance of strength versus reaction to balance recovery after being suddenly "perturbed" (as when standing on an accelerating bus, or being nudged in a crowd). In the video at left, the maximum lean angle is measured when the tether is not released, and performance depends only on strength. In the video at right, the maximum initial lean angle is measured when the tether is suddenly released, and performance depends on reaction time as well as strength. In the latter case, the maximum recovery angle is reduced by 60% on average, indicating the crucual role of reaction time and rate of torque generation.

 

Sample publications:

Hsiao-Wecksler, E.T., Robinovitch, S.N.: The effect of step length on young and elderly women's ability to recover balance. Clinical Biomechanics, 22: 574–80, 2007.

Mackey, D.C., and Robinovitch, S.N.: Mechanisms underlying age-related differences in ability to recover balance with the ankle strategy, Gait and Posture, 23(1): 59-68, 2006.

Robinovitch, S.N., Heller, B., Liu, A., and Cortez, J.: Effect of strength and speed of torque development on balance recovery with the ankle strategy. Journal of Neurophysiology, 88: 613-620, 2002.