Older adult balance and ankle control during a dual task
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Falls in older adults are a major public health concern. While both cognitive and physical changes in older adults have been studied, there has not been a clear connection made between the two. It has been suggested that there may be neural “competition” between cognitive and muscular tasks within the central nervous system, leading to balance problems in older adults. In the recent literature, joint stiffness has been identified as the balance mechanism competing with the cognitive task. This study compared balance during quiet stance to balance with a cognitive task, or dual task. It was hypothesized that older adults performing a dual task will have decreased joint stiffness at the ankle and decreased muscle activation in the ankle plantarflexion and dorsiflexion muscles. Joint stiffness was modelled as an inverted pendulum with rotational stiffness around the ankle. Eight active women between the ages of 65 and 84 participated in the study. Subjects performed four separate tasks: cognitive practice, cognitive task, static balance posturography, and dual cognitive and balance task. Results indicate that ankle stiffness (p<0.001), bilateral tibialis anterior muscle activity (p<0.025, p<0.011), and right lateral gastrocnemius muscle activity (p=0.025) increase during the dual task when compared to the balance or cognitive baselines. Significant changes were not observed for other lower leg muscle activations. The results do not fully support the hypothesis; however, the data suggests a relationship between the cognitive and muscular demands of the dual task.