Age difference in using a rapid step to regain balance during a forward fall

Background. Earlier studies showed that healthy old adults have substantially reduced abilities to develop joint torques rapidly. We hypothesized that this age decline would reduce abilities to regain balance once a forward fall is underway. The present study examined whether aging in fact reduces ability to regain balance by taking a single, rapid step upon release from a forward lean. Methods. Ten young (mean age 24.3 yr) and ten old (72.8 yr) healthy males were released from a forward-leaning position and instructed to regain standing balance by taking a single step forward. Lean angle was successively increased until a subject failed to regain balances as instructed. Lower extremity motions and foot-floor reactions were measured during the responses. Total response time was divided into reaction, weight transfer, and step times. Results. At small lean angles, responses of old subjects were similar 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 group, maximum lean angle correlated strongly with weight transfer time step velocity. Conclusion. Substantial age-related declines in the ability to regain balance by taking a rapid step exist among healthy adults when the time available for recovery is short. The source of the decline seems largely to lie in the decrease with age of maximum response execution speed rather than in the sensory or motor programming processes involved in response initiation.