Article

With aging, individuals' gaits become slower and their steps shorter; both are
thought to improve stability against balance threats. Recent studies have shown
that shorter step lengths, which bring the center of mass (COM) closer to the
leading foot, improve stability against slip-related falls. However, a slower
gait, hence lower COM velocity, does the opposite. Due to the inherent coupling
of step length and speed in spontaneous gait, the extent to which the benefit of
shorter steps can offset the slower speed is unknown. The purpose of this study
was to investigate, through decoupling, the independent effects of gait speed and
step length on gait stability and the likelihood of slip-induced falls.
Fifty-seven young adults walked at one of three target gait patterns, two of
equal speed and two of equal step length; at a later trial, they encountered an
unannounced slip. The results supported our hypotheses that faster gait as well
as shorter steps each ameliorates fall risk when a slip is encountered. This
appeared to be attributable to the maintenance of stability from slip initiation
to liftoff of the recovery foot during the slip. Successful decoupling of gait
speed from step length reveals for the first time that, although slow gait in
itself leads to instability and falls (a one-standard-deviation decrease in gait
speed increases the odds of fall by 4-fold), this effect is offset by the related
decrease in step length (the same one-standard-deviation decrease in step length
lowers fall risk by 6 times).
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