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ABSTRACT
Background: Postural control improvements in external focus and cognitive task conditions are thought to occur because directing attention away from postural control allows greater automaticity. We aimed to support this theory by using three dynamic measures of postural control that may reveal changes in the structure or composition of sway: the discrete wavelet transform, sample entropy, and rambling trembling analyses.
Methods: We analyzed the center of pressure data from twenty-two healthy young adults (20.8 ± 2.82 years) and twenty healthy older adults (69.02 ± 3.47 years). Participants stood with feet together in five conditions: baseline standing, internal focus, external focus, easy cognitive task, and difficult cognitive task. Analyses of variance were used to examine the effect of condition and age on the three dynamic measures.
Results: The wavelet transform revealed a shift toward greater contributions from higher frequency bands in cognitive task conditions, suggesting greater automaticity. Sample entropy was higher in cognitive task conditions, suggesting more complex sway and automatic control. The external focus and difficult cognitive tasks increased trembling in young adults, suggesting increased contributions from spinal reflex components.
Conclusion: Results support the theory that stability improvements in cognitive task conditions were due to automaticity in young and older adults. They also suggest that tasks that are more difficult are better at promoting automaticity than tasks requiring less cognitive involvement.