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.