Adaptive changes in anticipatory postural adjustments with novel and familiar postural supports.

Anticipatory postural adjustments (APAs) serve to stabilize posture prior to initiation of voluntary movement. This study examined the effects of changes in postural support on APAs using novel and familiar support paradigms. We also investigated whether postural strategies were refined with practice and how the CNS responded when multiple supports were available. Twelve healthy subjects stood on dual force platforms and performed 20 randomized left and right rapid leg-lift tasks in response to a visual cue under four conditions: unsupported, bilateral handgrip, bite plate, and a combined handgrip and bite plate condition. Vertical ground reaction forces, electromyography of limb, trunk and jaw muscles, and forces exerted on the support apparatus were recorded. Shift in center-of-pressure amplitude and duration were reduced with increased support. Muscles were recruited in advance of the focal movement when able to contribute to stability, and activity was modulated based on the amount of support available. The CNS adapted anticipatory postural strategies immediately with changes in condition regardless of familiarity with the support; however, adaptation was only complete at the first repetition in conditions that involved familiar support strategies. Tasks that involved a novel bite strategy continued to adapt with practice. In the multiple support condition, both hand and bite strategies were immediately incorporated; however, the contribution of each was not identical to conditions where supports were provided individually. This study emphasizes the flexibility of the CNS to organize postural strategies to meet the demands of postural stability in both familiar and novel situations.