Coordination of upper and lower body during balance recovery following a support translation

Strategies for recovery of posture were studied after lateral mechanical perturbations. 11 participants standing in tandem stance were unexpectedly submitted to lateral support translations with the eyes open or closed at two translation amplitudes. The trajectories of the center of mass of the upper and lower body and muscle activities allowed identification of three strategies, involving either the ankle or the hip only, or both. Hip use increased with vision and with amplitude of perturbation. Short-to-medium latency electromyographic activities were observed in leg and trunk muscles, and long-latency responses in the back leg muscles. Vision increased the activity of both leg and trunk muscles but did not influence the onset of the muscular responses. These data suggest a hierarchy in the selection of these different strategies: the hip is mobilized when the perturbation is more destabilizing but this strategy has a cost and needs specific sensory information supplied by vision.