Postural Control Strategies for Sensorimotor Training Based on Efficient Sensory Reweighting
Madi Dewan, Birendra
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To devise an optimized intervention for patients with balance problems due to sensory integration deficits, it is necessary to understand the adaptation in postural control strategy that is associated with the best use of sensory information; in other words, the efficient sensory reweighting for maintaining balance. Yet, the optimal postural control strategies adapted during efficient adaptation in sensory reweighting have not been investigated in both young and older adults. The purpose of this study was to identify and differentiate the optimal postural control strategies associated with efficient sensory reweighting adapted by healthy young adults during the specific sensory integration tasks (study 1), and to compare these adaptations to those of healthy older adults to determine the effect of age-related changes (study 2). Study 1 incorporated a multivariate design, and study 2 incorporated a mixed-factorial design. Thirty-six young healthy subjects (19 males and 17 females, age: 23.5 ± 2.3 years, height: 171.8 ± 10 cm, mass: 74.3 ± 14.8 kg) and fourteen older healthy subjects (6 males and 8 females, age: 66.96 ± 4.96 years, height: 166.6 ± 10 cm, mass: 74.4 ± 16.5 kg) participated in the study. Participants performed standing balance tasks in three conditions with progressively increasing amplitudes of visual (VIS), somatosensory (PLAT) and both (VISPLAT) systems perturbation. Adaptation in the postural control strategy was measured as changes in motor variables; muscle activities and joint angles. Contribution of the perturbed sensory input in maintaining postural stability was calculated to determine efficient sensory reweighting. In study 1, linear discriminant analysis was performed to discriminate the optimal postural control strategies adapted during the sensory integration tasks. In study 2, a 2 age-group × 3 condition mixed-factor ANOVA was performed for each motor variable. Hochberg alpha adjustment for multiple ANOVAs was performed separately for the family of EMG and joint angle variables. In study 1, there was a significant progressive decrease in postural sway per unit amplitude of sensory perturbation in each condition (p<.001), indicating an efficient sensory reweighting. Out of the two canonical discriminant functions produced, only the first function (LD1) was statistically significant in discriminating the conditions (p<.05) with a moderate canonical correlation coefficient of .44. LD1 separated VIS condition from PLAT and VIPLAT conditions the most. The optimal motor adaptation in the postural control revealed by LD1 during the VIS condition was increased muscle and joint adaptation activity around the neck, increased stability around the pelvis and decreased adaptation activity around the ankle. Similarly, during the PLAT and VISPLAT conditions, the optimal motor adaptation in postural control was decreased adaptation activity around the neck, increased mobility around the pelvis and increased adaptation activity around the ankle. The discriminant model produced an overall good prediction, 50% correct classification with prior probabilities of 33.33%, for the postural control tasks. In study 2, there was an efficient adaptation in sensory reweighting in the older adults comparable to the young adults. There was no significant group by condition interaction effect for any of the motor adaptation dependent variables (p > αadjusted). There was no significant main effect of the group and condition for any of the dependent variables (p > αadjusted). This indicates that there were similar postural control strategies for young and older adults in the three conditions. The motor strategies adapted during VIS was more pronounced in older adults compared to young adults due to relatively increased adaptation activity of the neck muscles and trunk muscles, and relatively decreased adaptation activity of the hip joint angle. The dissertation identified and discriminated the optimal postural control strategies associated with efficient sensory reweighting adapted by healthy young adults during the specific sensory integration tasks. The dissertation found that the adaptations of motor responses in older adults that are associated with efficient sensory reweighting are similar to those of the young adults. The age-related changes did not affect the relative pattern of optimal motor strategies in older adults compared to young adults but made them more pronounced, especially when the visual system was perturbed. Understanding the optimal postural control strategies associated with efficient sensory reweighting in healthy young and older adults can provide a clinician with a frame of reference from which to guide intervention and target the optimized goal of rehabilitation to minimize fall risk in older adults and patients with specific sensory integration impairments. Future research should develop and evaluate the efficacy of the intervention approach based on optimal postural control strategies in these populations.