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Age Influences the Outcome of a Slipping Perturbation During Initial But Not Repeated Exposures

^a Department of Physical Therapy, University of Illinois at Chicago
^b Departments of Physical Therapy and Human Movement Sciences, Northwestern University Medical School, Chicago, Illinois
^c Departments of Medicine, Northwestern University Medical School, Chicago, Illinois

Yi-Chung Pai, Department of Physical Therapy (MC 898), University of Illinois at Chicago, 1919 W. Taylor Street, Fourth Floor, Chicago, IL 60612 E-mail: cpai{at}uic.edu.

Background. Fall incidence in older adults might be reduced through learning to better recover from or adjust to perturbations. Extents of age-related declines and limitations in the ability to recover are not well established, however.

Methods. Slips were induced, using bilateral low-friction platforms, during a sit-to-stand task in 60 young and 41 older, healthy, safety-harnessed adults. Subjects underwent five slips, a block of nonslipping trials, then two reexposures to the slip. The first slip was novel and unexpected. Age-group and trial effects on fall incidence (evidenced by excessive hip descent) and on the direction of the initial protective step were examined.

Results. More older than young adults fell upon the first slip (73% vs 28%; p < .001). With repeated exposure, fall incidence decreased at similar exponential rates in both age groups. All but one subject eventually learned to slip without falling, and two-thirds of fallers fell only once. Repeat fallers fell without stepping in 63% of falls. Upon later slip reexposure, more older than young adults fell (20% vs 2%), but fewer falls occurred than did originally (p = .001). Likelihoods of forward and backward stepping during successful recovery changed with repeated slip exposure and upon reexposure, but did not differ between age groups.

Conclusions. Older adults are more likely to fall upon initial, unexpected perturbation exposure, but, upon repeated exposure, healthy young and older adults rapidly learn to avoid falling at a similar rate. Healthy older adults appear fully capable of learning to better recover from or adjust to a perturbation through repeated exposure.

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