Postural motor learning and the effects of age on practice-related improvements in compensatory posture control
Van Ooteghem, Karen
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The purpose of this thesis was to examine the capacity for acquisition and retention of practice-related improvements in compensatory posture control and the nature of postural motor learning among healthy young and older adults repeatedly exposed to continuous surface motion via a translating platform. Although much research has been conducted to examine the strategies adopted by the central nervous system to control posture in response to external perturbations, the learning capabilities of this system have remained relatively unexplored. Many of the studies that have explored practice-related changes in balance performance have focused on short-term adaptations to highly predictable stimuli. Borrowing from implicit sequence learning paradigms, we developed two experimental protocols to examine postural motor learning for a compensatory balance task in an environment with limited predictability. Applying key principles of motor learning to our experimental design including retention intervals and a transfer task enabled us to draw conclusions about the permanency and specificity of the observed changes. Our investigations revealed practice-related changes in the motor organization of posture control. In young adults, a shift in the complexity of the control strategy occurred which lead to improvements in spatial and temporal control of the COM. In contrast, a majority of older adults persisted with a simplified control strategy which restricted improvements in COM control. Importantly, despite control strategy differences, the two groups showed comparable rates of improvement in almost all outcome measures including measures of trunk stability and temporal COM control. Longer-term retention of behavioural changes provided evidence for learning in young adults. Similar maintenance of improvements was observed for some outcome measures in older adults. Where significant losses in performance occurred in this group, retention was evident in the rapid reacquisition of performance to the level of proficiency achieved in original practice. Based on these results, we concluded that age affected the adapted control strategy but not the capacity for postural motor learning. Further, regardless of age or protocol, the pattern of postural perturbations did not influence acquisition of a strategy of stability and thus, we concluded that postural motor learning under the current conditions was non-specific, that is, it did not involve sequence-specific learning. These results provide important insight into the generalized nature of compensatory postural motor learning and subsequently, into the potential for positive transfer of balance skill to other balance tasks.