Sudden turns and stops while walking: kinematic sources of age and gender differences

Background: Significant age and gender differences were found among healthy young and older adult subjects in their abilities to quickly turn or stop in order to avoid obstacles that suddenly appear in the gait path (Cao C, Ashton-Miller JA, Schultz AB, Alexander NB. Abilities to turn suddenly: effects of age, gender and available response time. J Gerontol Med Sci 1997;52A:M88–M93; Cao C, Ashton-Miller JA, Schultz AB, Alexander NB. Abilities to stop suddenly: effects of age, gender, gait phase, and available response time. Submitted for publication, 1997 (also available as a chapter in Cao C. Biomechanics of forward momentum arrest when walking: age and gender differences. PhD Dissertation, University of Michigan, 1996). The present study quantified the extent to which age and gender differences in those subjectsʹ response kinematics affected the total time they needed to suddenly arrest their forward momentum. Methods: Age- and gender-group means of four measures of forward movement of the anterior surface of the abdomen were obtained: the duration of the first post-cue response phase, from the visual cue that initiated the arrest response to reaching peak velocity (T1); acceleration (A1) during this phase; and decelerations (D2 and D3) during two subsequent post-cue response phases. A three-line-segment representation of this forward velocity history was constructed. This representation was used to predict the differences in response time needed (NRT) to suddenly arrest momentum that resulted from measured age and gender differences in each of the four response kinematics measures. Results: The largest contributor to the age group difference found in NRT was the increase in T1 among the older adults. Among the older males, the next largest contributor was their larger value of A1, and among the older females, their substantially smaller value of D2. Among the young adults in sudden turns, no single kinematic parameter seemed primarily responsible for the gender difference found in the NRT. Among the older adults, the gender difference in D2 was almost fully responsible for the gender difference in NRT, in both sudden stops and turns. Conclusions: Much of the older adultsʹ need for longer response times than those of the young was attributable to the lengthened first phase of their responses. Older females, in addition, needed longer response times than young adults or older males because, during the second phase of their responses, their decelerations were substantially smaller. These age and gender differences may have arisen in part from known age and gender differences in abilities to develop lower extremity joint torque strengths rapidly.