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Abstract:
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Falling during walking leads to millions of emergency room visits every year for all age groups and is a significant medical concern . While gait training has shown some promise for fall prevention , we know relatively little about how humans maintain stability , how we can quantify it and how we can use this knowledge to increase the success of fall prevention training . In this dissertation , I studied how human stability responds to continuous , small magnitude perturbations and to voluntary changes in gait characteristics by examining movement variability and long -term and instantaneous dynamic stability . In the first set of experiments , participants were exposed to continuous , pseudo -random external perturbations of the visual field and support surface in a Computer Assisted Rehabilitation ENvironment (CAREN ) . Participants exhibited increased step widths , shorter step lengths and increased step variability , orbital and short -term local instability . Despite this , mean instantaneous lateral stability remained approximately constant . In the second set of experiments , participants voluntarily adopted changes in their step widths and step lengths . Wider steps were associated with increased step width variability , decreased nonlinear stability , decreased anterior -posterior margins of stability and increased instantaneous lateral stability . Shorter steps were associated with decreased short -term and orbital stability but did not affect mean instantaneous stability . When instantaneous stability was examined between steps , as opposed to as an average over many steps , results from both studies indicated a relationship between each step’s stability and the stability of the immediately preceding step . From these studies , we now know that unpredictable , continuous perturbations during human walking applied in a given direction can be used to elicit predictable responses in motion variability and stability in that same direction . We know that the type of stability examined can influence the conclusions drawn about an individual’s stability during perturbed walking . For example , an individual’s variability may indicate increased risk of falling while he or she simultaneously demonstrates increased orbital stability and instantaneous lateral stability . A challenge faced in this area of research will be to understand how quantitative measures of stability relate to how we perceive our stability . |