Visual-Vestibular Interaction For Maintaining Stability While Standing Up From A Sitting Position: Effects Of Aging
Lui, Kai Yan
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Background: Sit-to-stand is a challenging task as it requires the transition from a large 3-point base of support to a small 2-point base of support while simultaneously controlling anteroposterior and vertical body acceleration. Age-related morphological changes in both the visual and vestibular system could impair the ability to extract and interpret sensory information necessary for motor control in older adults, which can increase instability and the risk of falls. The purpose of this study is to understand the effects of aging on visual-vestibular interaction for maintaining stability during sit-to-stand. Methods: Fifteen younger (age=22.5±1.1) and fifteen older (age=73.9±5.3) healthy adults were asked to stand from a sitting position as quickly as possible. Vestibular input was manipulated using percutaneous bipolar galvanic vestibular stimulation where threshold intensity was individually calculated for each participant during quiet stance with eyes closed. Galvanic vestibular stimulation was applied at both threshold (1xGVS) and 2-times the participant’s threshold intensity (2xGVS). Visual conditions included eyes opened, wearing custom-made vision blurring goggles, or eyes closed. Outcome measures included a global measure of performance (transition phase duration), mediolateral stability (peak-to-peak trunk roll angle, mediolateral center of mass displacement, mediolateral center of pressure displacement) and anteroposterior stability (peak braking force, peak-to-peak trunk pitch angle, and peak anteroposterior center of mass velocity). Results: When vision was suboptimal (blurring goggles), older adults had significantly longer transition phase duration than younger adults (p<0.05). Older adults demonstrated greater mediolateral instability than younger adults. When vision was absent, trunk roll angle was significantly greater with 1xGVS than 2xGVS (p<0.05). Mediolateral center of mass displacement was greater when vision was absent than when vision was available, irrespective of age (p<0.05). No effects of age, vision or galvanic vestibular stimulation were seen in peak braking force, trunk pitch angle, and peak anteroposterior center of mass velocity (p>0.05). Conclusion: Regardless of age, visual inputs were more critical to maintain stability during sit-to-stand than vestibular inputs. Differences between younger adults and older adults were only seen in the mediolateral direction. Despite having greater mediolateral instability, older adults utilized similar strategies as younger adults to overcome sensory perturbations during sit-to-stand.