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

OBJECTIVES: To investigate the influence of different reaction stimulus cues on the characteristics of ground reaction forces during the initiation of rapid forward stepping, and to determine whether age-related differences in step initiation are influenced by the type of stimulus cue used to trigger stepping. DESIGN: Case-control study. SETTING: University-based research laboratory. PARTICIPANTS: Fifteen healthy younger adults and 35 community-dwelling older adult volunteers. MAIN OUTCOME MEASURES: Subjects performed forward step initiation in response to 3 different reaction stimulus cues (light, sound, electrocutaneous) during simple reaction-time conditions. Ground reaction force data were collected and used to characterize the timing and magnitude features of the postural (weight-transfer) and step components. RESULTS: In comparison with the light and sound stimuli, the nonnoxious electrocutaneous trigger cue was associated with an increase in the magnitude of the initial displacement of the center of pressure (COP) in the mediolateral direction. Overall, older subjects were slower to initiate the postural and step components, and displayed a reduction in the initial posterior displacement of the COP. CONCLUSIONS: The postural component for lateral weight transfer was augmented by the electrocutaneous trigger cue, suggesting its potential to enhance step initiation among clinical populations. Age-related changes in stepping were unaffected by the type of stimulus cue, but the older group had a slower response initiation time and less forward propulsion. The abilities of many older persons may be compromised in situations where rapid adjustments in the base of support through stepping are triggered by environmental stimuli.