AGE DIFFERENCE IN USING A RAPID STEP TO REGAIN BALANCE DURING A FORWARD FALL

Background. Earlier studies showed that healthy old adults have substa ntially reduced abilities to develop joint torques rapidly. We hypothe sized that this age decline would reduce abilities to regain balance o nce a forward fall is underway. The present study examined whether agi ng in fact reduces ability to regain balance by taking a single, rapid step upon release from a forward lean. Methods. Ten young (mean age 2 4.3 yr) and ten old (72.8 yr) healthy males were released from a forwa rd-leaning position and instructed to regain standing balance by takin g a single step forward. Lean angle was successively increased until a subject failed to regain balances as instructed. Lower extremity moti ons and foot-floor reactions were measured during the responses. Total response time was divided into reaction, weight transfer, and step ti mes. Results. At small lean angles, responses of old subjects were sim ilar to those of the young. However, the mean maximum lean angel from which old could regain balance as instructed was significantly smaller than that for young (23.9 vs. 32.5 deg, p < .0005). Within each age g roup, maximum lean angle correlated strongly with weight transfer time step velocity. Conclusion. Substantial age-related declines in the ab ility to regain balance by taking a rapid step exist among healthy adu lts when the time available for recovery is short. The source of the d ecline seems largely to lie in the decrease with age of maximum respon se execution speed rather than in the sensory or motor programming pro cesses involved in response initiation.