Abstract
During walking in neurologically-intact controls, larger mediolateral pelvis displacements or velocities away from the stance foot are accompanied by wider steps. This relationship contributes to gait stabilization, as modulating step width based on pelvis motion (hereby termed a “mechanically-appropriate” step width) reduces the risk of lateral losses of balance. The relationship between pelvis displacement and step width is often weakened among people with chronic stroke (PwCS) for steps with the paretic leg. Our objective was to investigate the effects of a single exposure to a novel force-field on the modulation of paretic step width. This modulation was quantified as the partial correlation between paretic step width and pelvis displacement at the step’s start (step start paretic ρdisp). Following 3-minutes of normal walking, participants were exposed to 5-minutes of either force-field assistance (n = 10; pushing the swing leg toward mechanically-appropriate step widths) or perturbations (n = 10: pushing the swing leg away from mechanically-appropriatestep widths). This period of assistance or perturbations was followed by a 1-minute catch period to identify after-effects, a sign of altered sensorimotor control. The effects of assistance were equivocal, without 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 a positive after-effect (p = 0.02). These results suggest that PwCS can strengthen the link between pelvis motion and paretic step width if exposed to a novel mechanical environment. Future work is needed to determine whether this effect is extended with repeated perturbation exposure.
Highlights
C OMMUNITY-DWELLING people with chronic stroke (PwCS) have an elevated fall-risk, with falls most commonly occurring during walking [1]
We investigated whether a single exposure to assistive or perturbing forces influenced the relationship between pelvis motion and step width in PwCS, with results partially supporting our hypotheses
Perturbation cessation was followed by a period of after-effects in which the relationship between pelvis displacement at the start of a step and paretic step width was strengthened relative to baseline, indicative of altered sensorimotor control
Summary
C OMMUNITY-DWELLING people with chronic stroke (PwCS) have an elevated fall-risk, with falls most commonly occurring during walking [1]. Balance deficits have been assessed using metrics of varying complexity, generally finding that relative to age-matched controls, PwCS tend to walk with: shorter and wider steps; more variable step lengths, times, and widths; more variable mediolateral and anteroposterior margins of stability; and larger mediolateral and vertical local divergence exponents (measuring the response to small perturbations) [3]–[5] Several of these metrics can prospectively predict falls among PwCS (i.e. decreased step length, increased step time and length variability, increased local divergence exponent for mediolateral sacrum motion) [6]. In PwCS, the relationship between pelvis motion and step width is weaker for paretic steps, quantified using the partial correlation between mediolateral pelvis displacement and step width (ρdisp) [12] This paretic side deficit is likely due in part to altered active control, as the normal link between pelvis motion and paretic swing phase gluteus medius activity is disrupted in PwCS with poor balance [13]
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