External-lateral perturbations affect the center of pressure displacement in the medial-lateral direction prior to step initiation

Controllability of posture in the medial-lateral direction is determined as a critical capacity for balance maintenance in step initiation. Eleven young healthy participants stood on the force platform and instructed to take a step while experiencing a pendulum perturbation from the lateral side of the right shoulder. The COP displacements and body movements were recorded and analyzed. The postero-lateral COP points on the swing and stance sides were marked and the two distances were calculated. The temporal events of COP and body movements were not significantly different between the experimental conditions. The COP distance on the stance side in the medial-lateral direction was significantly affected by the perturbation. The sequence of how the CNS initiated a step was not affected by the step side and perturbation. Changes in the medial-lateral COP distance from the swing to stance side were affected in response to the lateral perturbation.