The Role of Predictability of Perturbation Magnitudes in Control of Posture

People frequently experience perturbations while standing in crowded areas or when interacting with external objects. Balance impairment is common in older adults with mild cognitive impairment (MCI). Balance maintenance in response to a perturbation is affected by predictability of magnitude of body disturbance. The purpose of the dissertation was to investigate postural control associated with exposures to perturbations of different magnitudes. In study 1, twenty young adults received pendulum perturbations of small or large magnitudes induced in sagittal plane. In study 2, twenty young adults received external perturbations induced in vertical plane by catching objects of small or large magnitudes. In study 3, ten young adults performed self-initiated perturbations induced by lifting either light or heavy objects. In study 4, twelve healthy older adults and twelve young adults received pendulum perturbations of small or large magnitudes and in study 5, fifteen individuals with MCI and fourteen age-matched control participants received pendulum perturbations of small or large magnitudes. All participants were not told about perturbation magnitudes, so they were exposed to a perturbation of either known magnitude (as such, predictable) in condition of repetitive magnitude or unknown magnitude (unpredictable) in condition of the unpredictable change of perturbation magnitude. Electromyographic activity of leg and trunk muscles and center of pressure (COP) displacements were recorded and analyzed during anticipatory (APAs) and compensatory (CPAs) phases of postural control. The outcomes of studies 1, 2 and 3 involving body perturbations induced by three different tasks showed similar trend revealing that when the perturbation magnitude suddenly changed, the participants tended to rely on prior experiences in dealing with perturbations and required less than six trials to adjust APAs and CPAs to new perturbation magnitude. The results of study 4 showed that smaller APAs in older adults were observed as compared to young adults in predictable conditions. Older adults also required more trials to optimize postural adjustments, as compared to young adults. The results of study 5 showed that individuals with MCI demonstrated smaller APAs in unpredictable conditions and required more trials to optimize postural adjustments, as compared to healthy older adults. The findings suggest that aging and cognitive decline adversely affect abilities to predict perturbation magnitude.