Leveraging Sensorimotor Adaptive Generalizability to Minimize Dynamic Fall Risk
Madansingh, Stefan Ishan
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Post-flight balance control disturbances have long been a focus for the human spaceflight program and recently an effort to identify predictors of sensorimotor adaptation to microgravity has been proposed to customize and enhance the efficacy of space flight countermeasures. Balance related changes due to sensorimotor adaptation in the microgravity environment are of particular interest due to increased locomotor dysfunction and risk of falls – real risks for astronauts returning home or embarking on discovery missions. Unfortunately, there is no single technique or countermeasure to address these issues, and their severity is highly individualized. This dissertation explored within-individual sensorimotor adaptation performance during manual and locomotor control tasks, as well as recovery responses to whole-body gait perturbations, such as slips and trips. It was hypothesized that individuals adept at achieving motor adaptation during manual control would show improved adaptation performance during a locomotor adaptation task, as a result of effective forward model updating in the cerebellum. By better understanding motor adaptation performance within individuals, it was further hypothesized that whole-body postural recovery to locomotor challenges would be related to this performance, predicting trip and slip recovery step reaction time, recovery step force and time to recover to normal gait. Finally, this dissertation assessed the effectiveness of a novel split-belt treadmill slip and trip perturbation system to produce challenging and unpredictable locomotor stressors, for which practice and training of opposing tasks would show minimal transfer effects. A population of 58 healthy, college-aged participants (30 female) performed two sensorimotor adaptation tasks: a rotated-input joystick matching task and a 3:1 split-belt walking protocol, and navigated a block-randomized set of 10 trip and 10 slip perturbations to characterize postural recovery during locomotion. A pair of exponential curve fits were used to estimate adaptation performance in the two sensorimotor tasks. Whole-body motion capture and treadmill force-plates captured postural recovery kinematics and kinetics. The results of this dissertation identified a strong relationship among manual and locomotor adaptation performance (r = 0.799), suggesting adaptation performance may be centrally mediated by a common mechanism, likely located within the cerebellum. Individual split-belt adaptation performance was also observed to be predictive of slip recovery time after a bout of training (r = 0.338), as well as trip (r = 0.427) and slip (r = 0.312) recovery time improvement (% change) after a bout of 10 perturbations. This suggests a level of strategic motor adaptation related to plastic adaptation performance, within-individuals, in a set of very challenging discrete motor tasks. Finally, all participants were observed to improve significantly in recovery step force and time to recover after repeated slip or trip perturbations, but there were no meaningful transfer effects of a bout of trip training (10 perturbations) upon a novel slip, nor a bout of slip training (10 perturbations) upon a novel trip. Taken together, these results are the first to show a strong individualized link among manual and locomotor adaptation tasks, and significant correlations between adaptation performance and whole-body postural recovery during slips and trips. It is suggested that these relationships represent a deeper, generalizable connection among short-term strategic adaptation and traditional plastic adaptation observed during a simple motor adaptation task, bridging a previously unobserved gap between discrete and continuous motor control tasks.