THE ROLE OF CONSCIOUSNESS IN BALANCE PERFORMANCE.

Background: Traditional centre of pressure (COP) measures do not account for the complex dynamics of postural control. Researchers have suggested that complexity-based COP measures not only describe the dynamic characteristics of sway but also inform about conscious control in balance. However, limited evidence is available for this claim. Aim: To examine the relationship between traditional and complexity-based COP measures and the propensity for conscious control of movements. Methods: Three groups, consisting of 53 young adults, 39 older adults with a history of falling, and 39 older adults without a history of falling, were asked to perform single- and dual-task quiet standing balance tasks. Four traditional COP measures were recorded: ellipsoidal area (85.35%), average velocity, standard deviation of medial-lateral and anterior-posterior axis. Additionally, four complexity-based measures were recorded: sample entropy and detrended fluctuation analysis for medial-lateral and anteriorposterior axis. Propensity for conscious control of movements was measured using the Movement Specific Reinvestment Scale. Results: The results showed that a higher propensity for conscious control of movements was associated with a more constrained (less complex) mode of balancing and more variable sway in the medial-lateral direction in young adults. The association was not apparent under dual-task conditions during which participants' attention was diverted away from the balancing task. Furthermore, no relationship was apparent between postural control and propensity for conscious control of movements in older adult fallers or nonfallers. Conclusions: It is of clinical importance to understand how consciousness affects postural control. Our findings show that complexity-based COP measures are indicative of conscious involvement in postural control in young adults. The absence of such relationships in the older adults raises questions about the underlying conscious and unconscious mechanisms of balance in older adults. ABSTRACT FROM AUTHOR