EFFECTS OF AGE AND AVAILABLE RESPONSE-TIME ON ABILITY TO STEP OVER AN OBSTACLE

Background. Falls during walking are often triggered when a foot contacts an obstacle in its path. Yet little is known about the ability of individuals of any age to successfully negotiate obstacles, especially under time-critical conditions. Methods. The gait Of 24 young and 24 old healthy adults (mean ages 23 and 73 years) was studied as they approached and tried to avoid stepping on a band of light, not knowing when or where it might appear on an 8 m-long walkway. This virtual obstacle was placed at the predicted location of the next footfall with available response times (ART) before heel strike that were varied randomly in 50 ms increments from 200 to 450 ms. In addition, their gait was observed as they stepped over a fixed virtual obstacle and over an obstacle that appeared with approximately a 1000 ms ART. Results. The old had an increased risk of obstacle contact while negotiating obstacles under time-critical conditions (p .082). Mean rates-of-success (RS) in obstacle avoidance for the young ranged from .205 at a 200 ms ART to .969 at a 450 ms ART. Corresponding mean RS for the old were .157 and .920. Lower extremity simple reaction time (SRT) tests made under static conditions showed that the mean SRT of the old were approximately 80 ms longer than those of the young. Regression analyses suggested that the old in fact would have needed only 30 ms additional ART to achieve RS equal to that of the young for obstacles appearing with ART from 300 to 450 ms. Conclusions. Reductions in ART significantly decreased RS. Delays as small as 50 or 100 ms in observing or reacting to obstacles in real-life situations may significantly lower the rate of success that subjects of any age have in avoiding them. Age differences in SRT do not always reliably indicate age differences in obstacle avoidance under time-critical situations.