The influence of stimulus cue on the initiation of stepping in young and older adults

Objectives: To investigate the influence of different reaction stimulus cue s on the characteristics of ground reaction forces during the initiation of rapid forward stepping, and to determine whether age-related differences i n step initiation are influenced by the type of stimulus cue used to trigge r stepping. Design: Case-control study. Setting: University-based research laboratory. Participants: Fifteen healthy younger adults and 35 community-dwelling olde r adult volunteers. Main Outcome Measures: Subjects performed forward step initiation in respon se to 3 different reaction stimulus cues (light, sound, electrocutaneous) d uring simple reaction-time conditions. Ground reaction force data were coll ected and used to characterize the timing and magnitude features of the pos tural (weight-transfer) and step components. Results: In comparison with the light and sound stimuli, the nonnoxious ele ctrocutaneous trigger cue was associated with an increase in the magnitude of the initial displacement of the center of pressure (COP) in the mediolat eral direction. Overall, older subjects were slower to initiate the postura l and step components, and displayed a reduction in the initial posterior d isplacement of the COP. Conclusions: The postural component for lateral weight transfer was augment ed by the electrocutaneous trigger cue, suggesting its potential to enhance step initiation among clinical populations. Age-related changes in steppin g were unaffected by the type of stimulus cue, but the older group had a sl ower response initiation time and less forward propulsion. The abilities of many older persons may be compromised in situations where rapid adjustment s in the base of support through stepping are triggered by environmental st imuli.