Independent influence of gait speed and step length on stability and fall risk

Abstract

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).

Estabilidade da marcha de adultos em diferentes condições visuais: estudo piloto

“…However, the results suggest no alterations in spatiotemporal parameters or gait stability with changing visual condition. Unstable gait is associated with slower walking 7,18 . The lack of differences in walking stability may be explained by the maintenance of gait velocity.…”

“…This fact indicates that a partial reduction in lighting in subjects with good visual acuity may not be sufficient to reduce gait velocity. Slower gait usually causes a reduction in step length as an adaptation to prevent falls 7 . The lack of changes in step length may therefore be due to the maintenance of gait velocity.…”

“…Since gait velocity is strongly correlated with COM VEL 24 , the maintenance of velocity under the different light conditions maintained all stability parameters related to COM VEL . In the case of adaptation to slower walking speeds, step length should decrease to prevent the loss of stability and risk of falls 7 . Visual perturbations do not impose changes during walking, but rather cause motor adaptations characterized by relatively individual responses to permit gait control 15 .…”

“…The margin of stability and time-to-contact, respectively correspond to the distance and time when a new step needs to be performed to recover stability. Parameters such as walking speed, step length and cadence are also related to gait stability 7,8 . The visual system plays a key role in the control of this stability during walking, contributing to the orientation of locomotion and route planning 9 .…”

“…The same gait adaptations are observed in children walking in the dark 13 , in subjects walking in a virtual reality environment which induces conflicts to the visual system 14,15 , and in subjects with visual problems 12,16,17 . Apparently, these patterns are adopted as a strategy to keep the COM close to the BOS, maintaining a careful gait as seen when walking in situations with an increased risk of slipping 7 or in elderly populations with a history of falls 18,19 . However, the level of dependence of gait stability characteristics on vision is unclear.…”