The Influence of Age on Compensatory Stepping Thresholds
Crenshaw, Jeremy R.
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The effects of increasing age on anterior and posterior compensatory stepping thresholds were studied. Young (18-35 years of age), middle-aged (55-64 years), and older (65 years and older) adults responded to anterior and posterior disturbances from surface translations. Stepping thresholds were defined as the disturbance displacements beyond which a single or second compensatory step was elicited. It was hypothesized that stepping thresholds would be reduced with increasing age. As an exception, it was hypothesized that posterior, single-stepping thresholds would not be reduced with increasing age. When disturbances were delivered as subjects were standing, and subjects were instructed to “try not to step," our hypotheses were supported. Young adults demonstrated larger anterior single-stepping thresholds than that of middle-aged and older adults. No influence of age on posterior single-stepping thresholds was observed. When, disturbances were delivered as subjects were standing, and subjects were instructed to “try to take only one step," our hypotheses were partially supported. Young adults demonstrated larger anterior multiple-stepping thresholds than middle-aged and older adults. Young adults demonstrated larger posterior multiple-stepping thresholds than older adults, but not middle-aged adults. When disturbances were delivered as subjects walked, and subjects were instructed to “try to take only one step”, our hypotheses were partially supported. A significant, yet weakly correlated decline in anterior, multiple-stepping thresholds was observed with increasing age. Young adults demonstrated larger posterior multiple-stepping thresholds than older adults and middle-aged adults at the lowest peak treadmill belt velocity. Regardless of initial condition, no significant differences were observed between the thresholds of middle-aged and older adults. The observed, age-related effects on the compensatory stepping response, manifested at an age as early as 55 years, are novel findings of clinical importance. Collectively, the results of this work identify potential targets for fall-prevention interventions. These targets include enhancing the muscular response of the lower extremities so that a disturbance imparts less dynamic instability and trunk rotation, as well as lengthening of the compensatory step. Interventions that are designed to focus on these targets and that consider the principle of specificity have potential for successful fall prevention.