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Noah Rosenblatt and Mark D. Grabiner

The expected rise in the number of older adults in the coming decades may exacerbate the social, medical and economic problems posed by falls and fall-related injuries. In part, the growing urgency for effective solutions refects the apparently constant average annual rate of falls by older adults over the past 30 years. Exercise by older adults can significantly reduce fall risk. However, the extent to which it does so raises the question as to whether its effectiveness can be increased. Results from recent studies support the view that avoiding a fall following a large postural disturbance is a complex motor skill that can be significantly improved by practice and thereby reducing fall risk. This reduction in fall risk appears to exceed that achieved by previously reported interventions. The principles on which the associated training protocol is based fall clearly within the discipline of kinesiology.

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Noah J. Rosenblatt, Christopher P. Hurt, and Mark D. Grabiner

Recent experimental findings support theoretical predictions that across walking conditions the motor system chooses foot placement to achieve a constant minimum “margin of stability” (MOSmin)—distance between the extrapolated center of mass and base of support. For example, while step width varies, similar average MOSmin exists between overground and treadmill walking and between overground and compliant/irregular surface walking. However, predictions regarding the invariance of MOSmin to step-by-step changes in foot placement cannot be verified by average values. The purpose of this study was to determine average changes in, and the sensitivity of MOSmin to varying step widths during two walking tasks. Eight young subjects walked on a dual-belt treadmill before and after receiving information that stepping on the physical gap between the belts causes no adverse effects. Information decreased step width by 17% (p = .01), whereas MOSmin was unaffected (p = .12). Regardless of information, subject-specific regressions between step-by-step values of step width and MOSmin explained, on average, only 5% of the shared variance (β = 0.11 ± 0.05). Thus, MOSmin appears to be insensitive to changing step width. Accordingly, during treadmill walking, step width is chosen to maintain MOSmin. If MOSmin remains insensitive to step width across other dynamic tasks, then assessing an individual’s stability while performing theses tasks could help describe the health of the motor system.