Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 53, Issue 6 M471-M480, Copyright © 1998 by The Gerontological Society of America
Inefficient postural responses to unexpected slips during walking in older adults
PF Tang and MH Woollacott
Department of Exercise and Movement Science and Institute of Neuroscience, University of Oregon, USA. [email protected]
BACKGROUND: Slips account for a high percentage of falls and subsequent
injuries in community-dwelling older adults but not in young adults. This
phenomenon suggests that although active and healthy older adults preserve
a mobility level comparable to that of young adults, these older adults may
have difficulty generating efficient reactive postural responses when they
slip. This study tested the hypothesis that active and healthy older adults
use a less effective reactive balance strategy than young adults when
experiencing an unexpected forward slip occurring at heel strike during
walking. This less effective balance strategy would be manifested by slower
and smaller postural responses, altered temporal and spatial organization
of the postural responses, and greater upper trunk instability after the
slip. METHODS: Thirty- three young adults (age range=19-34 yrs, mean=25+/-4
yrs) and 32 community-dwelling older adults (age range=70-87 yrs,
mean=74+/-14 yrs) participated. Subjects walked across a movable forceplate
which simulated a forward slip at heel strike. Surface electromyography was
recorded from bilateral leg, thigh, hip, and trunk muscles. Kinematic data
were collected from the right (perturbed) side of the body. RESULTS:
Although the predominant postural muscles and the activation sequence of
these muscles were similar between the two age groups, the postural
responses of older adults were of longer onset latencies, smaller
magnitudes, and longer burst durations compared to young adults. Older
adults also showed a longer coactivation duration for the ankle, knee, and
trunk agonist/antagonist pairs on the perturbed side and for the knee
agonist/antagonist pair on the nonperturbed side. Behaviorally, older
adults became less stable after the slips. This was manifested by a higher
incidence of being tripped (21 trials in older vs 5 trials in young adults)
and a greater trunk hyperextension with respect to young adults. Large arm
elevation was frequently used by older adults to assist in maintaining
trunk stability. In an attempt to quickly reestablish the base of support
after the slips, older adults had an earlier contralateral foot strike and
shortened stride length. CONCLUSION: The combination of slower onset and
smaller magnitude of postural responses to slips in older adults resulted
in an inefficient balance strategy. Older adults needed secondary
compensatory adjustments, including a lengthened response duration and the
use of the arms, to fully regain balance and prevent a fall. The shorter
stride length and earlier contralateral foot strike following the slip
indicate use of a more conservative balance strategy in older adults.
