An Evaluation of Balance Perturbation Paradigms and the Effect of Age on the Perturbation Characteristics Relationship
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The ability to recover balance to avoid falling following a postural perturbation is a critical aspect of mobility. Our knowledge of human balance recovery emanates from studies that have intentionally disrupted balance control. These studies have utilized a number of different postural perturbation methods and a variety of perturbation intensities, which makes it difficult to compare between studies, and which may have resulted in inconsistencies and disagreement in the scientific literature. Previous work has suggested that different postural perturbations may induce fundamentally different responses, though the literature is sparse. It is important to understand these differences before a selection of methods could be made to investigate potential balance deficits among different special populations (e.g. older adults; neurological patients). The purpose of the current dissertation was: 1) to directly compare two different types of perturbation, platform-translation and shoulder-pull, on balance-correcting responses, 2) to describe kinematic and neuromuscular responses to different perturbation methods, to explore similarities and differences in the nature of the responses associated with different perturbation methods, and 3) to examine the effect of age on the relationships between perturbation characteristics in determining the balance-correcting response. Four studies were conducted. Firstly, the perturbation characteristics, force and displacement, common to platform-translation and shoulder-pull methods were determined to allow for a reasonable comparison between balance-correcting responses induced by both perturbation methods. These characteristics were used in the second and third study, which: 1) explored differences in dynamic postural stability resulting from two different perturbation methods, and 2) explored similarities and differences in the organization of balance-correcting responses induced with both methods. The fourth study investigated the effect of age on the relationship between perturbation characteristics, which determine the type of balance correcting response (i.e. feet-in-place or stepping) using a shoulder-pull method. These studies suggest that while there are similarities in the balance-correcting responses between perturbation methods, there are also critical differences that are unique to the modes of perturbation utilized. The current dissertation underscores that caution is required when interpreting results of studies utilizing different perturbation methods and that individual differences between participants, which can mask age-related differences, need to be recognized.