A comparison between young and old adults in their ability to rapidly side-step during gait when attention is divided
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Dividing attention between a cognitive and a movement task has been shown to affect balance. The purpose of this study was to investigate the effects of divided attention, age and prior knowledge of movement, on ground reaction forces and the position of the center of mass (COM) relative to the center of pressure (COP) when individuals perform a rapid side-step while walking. Thirty-two young and 32 old adults participated in this study. Subjects walked and took a side-step without interrupting forward progression. An arithmetic task was performed during half of the walking trials with the sidestep direction preplanned or unknown. A three-way repeated measure ANOVA was used for data analysis. Side-step direction and dual or single task were the repeated measures. Adding a cognitive task did not significantly affect kinetic measures but did significantly affect the COM to COP distance. The COM to COP distance was greater in the single task trials than in the dual task trials for the young adults. The data suggest a willingness for the younger adults to accept more risk to balance. Prior knowledge of the side-step direction significantly affected some of the kinetic measures. The COM to COP distance was also affected but the differences were age-dependent. For the young adults, there was an increase in peak lateral force, and in distance between the COM and COP, when side-step direction was known. Keeping the COM closer to COP is a conservative dynamic balance strategy suggesting that the old adults did not, or could not optimize their movement pattern even when they knew the direction of the sidestep in advance. Overall, age-related differences were found for most of the dependent measures. Many daily activities require rapid response times at a relatively high speed of movement. The fact that older adults in the current study did not perform similarly to younger adults suggests that they are at increased risk for negative consequences when response time to a complex motor task must be performed simultaneously with a secondary cognitive task.