The effect of a cognitive task on voluntary step execution in healthy elderly and young individuals.

OBJECTIVES To investigate voluntary step behavior of healthy elderly individuals during single- and dual-task conditions and to compare it with those of young subjects. DESIGN Laboratory-based study. SETTING Tests of healthy elderly and young individuals from senior community centers and from the university population in Boston, Massachusetts. PARTICIPANTS Sixty-six elderly and 12 young subjects. MEASUREMENTS Forward, sideways, and backward rapid voluntary stepping performed as a reaction time task while standing on a force platform and (1) awaiting a cutaneous cue (single task) and (2) awaiting a cutaneous cue while performing an attention-demanding Stroop task (dual task). Step initiation phase, foot-off time, foot contact time, and preparatory and swing phases were extracted from center-of-pressure and ground reaction force data. RESULTS Elderly subjects were significantly slower than young in all step parameters under both conditions. For dual compared with single task, the initiation phase increased 108% in the elderly group and 34% in the young. There was a short-term learning effect during the dual task in elderly subjects but not in the young. CONCLUSION The disproportional increase in step initiation time during the dual task in the elderly group suggests that they lacked neural processing resources required for swift multitasking during a voluntary postural task. This may be a factor contributing to balance loss and the large number of falls in elderly persons. Training may improve this skill. Clinical tests of postural function should incorporate multitask conditions to capture a more complete assessment of an individual's ability.