A rapid upward step challenges medio-lateral postural stability

A rapid step up was compared with a rapid step forward to assess the challe nge they posed to postural stability in the medio-lateral (ML) direction. T he center of pressure (COP) motion, and hip abductor muscle activity were c ompared between the two tasks in nine young healthy subjects. Analysis reve aled that in the step up task there was a greater range and velocity of med io-lateral COP motion, an earlier gluteus medius onset time and a larger ma gnitude of gluteus medius activity than in the step forward task. The step up task appears to provide a greater challenge to ML postural stability tha n a step forward and thus may be an appropriate paradigm for the investigat ion of medio-lateral postural instability. (C) 2000 Elsevier Science B.V. A ll rights reserved.