During human walking, step width is predicted by mediolateral motion of the pelvis, a relationship that can be attributed to a combination of passive body dynamics and active sensorimotor control. The purpose of the present study was to investigate whether humans modulate the active control of step width in response to a novel mechanical environment. Participants were repeatedly exposed to a force-field that either assisted or perturbed the normal relationship between pelvis motion and step width, separated by washout periods to detect the presence of potential after-effects. As intended, force-field assistance directly strengthened the relationship between pelvis displacement and step width. This relationship remained strengthened with repeated exposure to assistance, and returned to baseline afterward, providing minimal evidence for assistance-driven changes in active control. In contrast, force-field perturbations directly weakened the relationship between pelvis motion and step width. Repeated exposure to perturbations diminished this negative direct effect, and produced larger positive after-effects once the perturbations ceased. These results demonstrate that targeted perturbations can cause humans to adjust the active control that contributes to fluctuations in step width.

During human walking, step width is predicted by mediolateral motion of the pelvis, a relationship that can be attributed to a combination of passive body dynamics and active sensorimotor control. The purpose of the present study was to investigate whether humans modulate the active control of step width in response to a novel mechanical environment. Participants were repeatedly exposed to a force-field that either assisted or perturbed the normal relationship between pelvis motion and step width, separated by washout periods to detect the presence of potential after-effects. As intended, force-field assistance directly strengthened the relationship between pelvis displacement and step width. This relationship remained strengthened with repeated exposure to assistance, and returned to baseline afterward, providing minimal evidence for assistance-driven changes in active control. In contrast, force-field perturbations directly weakened the relationship between pelvis motion and step width. Repeated exposure to perturbations diminished this negative direct effect, and produced larger positive after-effects once the perturbations ceased. Both of these results provide evidence of gradual changes in active control in response to perturbations. In the longer term, these methods may be useful for improving deficits in the active control of step width often observed among clinical populations with poor walking balance.

No abstract

Background. People with chronic stroke (PwCS) often exhibit a weakened relationship between pelvis motion and paretic step width, a behavior important for gait stabilization.We have developed a force-field able to manipulate this relationship on a step-by-step basis.Objective. The objective of this study was to investigate the effects of a single exposure to our novel force-field on the step-by-step modulation of paretic step width among PwCS, quantified by the partial correlation between mediolateral pelvis displacement at the start of a step and paretic step width (step start paretic ρdisp).Methods. Following a 3-minute period of normal walking, participants were exposed to 5-minutes of either force-field assistance (n=10; pushing the swing leg toward a mechanically-appropriate step width) or perturbations (n=10; pushing the swing leg away from a mechanically-appropriate step width). This period of assistance or perturbations was followed by a 1-minute catch period to identify any after-effects, a sign of sensorimotor adaptation.Results. We found that assistance did not have a significant direct effect or after-effect on step start paretic ρdisp. In contrast, perturbations directly reduced step start paretic ρdisp (p=0.004), but were followed by an after-effect in which this metric was increased above the baseline level (p=0.02).Conclusions. These initial results suggest that PwCS have the ability to strengthen the link between pelvis motion and paretic foot placement if exposed to a novel mechanical and is also made available for use under a CC0 license.

BackgroundMany people with chronic stroke exhibit walking balance deficits, which are linked with increased fall risk and decreased balance confidence. One potential contributor to these deficits is a decreased ability to adjust where the paretic foot is placed based on pelvis motion, which is an important factor in mediolateral walking balance.ObjectiveThe objective of this study was to investigate altered stepping behavior for steps taken with the paretic leg, and to explore the relationship between this behavior and clinical measures of balance and balance confidence.Methods.93 individuals with chronic stroke walked on a treadmill and completed a series of common clinical tests. We used partial correlations to quantify the step-by-step relationship between mediolateral pelvis displacement and both step width (ρSW) and mediolateral foot placement relative to the pelvis (ρFP), a metric that focuses on swing leg repositioning.ResultsρSW was weaker for steps taken with the paretic leg, whereas ρFP did not differ between non-paretic and paretic steps. Participants who walked faster had larger ρSW and ρFP values, but instructing participants to walk faster did not consistently increase ρSW or ρFP for paretic steps. Significant, albeit weak, relationships were observed between paretic ρSW and Functional Gait Assessment score, as well as between paretic ρFP and Activities-Specific Balance Confidence score, fear of falling, and fall history.ConclusionsA reduced ability to adjust where the paretic foot lands when taking a step may discourage fast walking speeds after a stroke and contribute to clinical observations of decreased walking balance.