Abstract
Community dwelling stroke survivors most often fall while walking. Understanding how post-stroke individuals control mediolateral footpath during walking may help elucidate the mechanisms that contribute to walking instability. By applying the Uncontrolled Manifold (UCM) approach, we investigated (1) how post-stroke individuals coordinate lower-extremity joint motions to stabilize mediolateral footpath of the swing leg, and (2) how the inter-joint coordination in footpath stabilization correlates to their walking stability. Nine stroke subjects and nine healthy controls walked on a treadmill at four different speeds. UCM analysis partitions the variance of kinematic configurations across gait cycles into “good variance” (i.e., the variance component leading to a consistent footpath) or “bad variance” (i.e., the variance component leading to an inconsistent footpath). We found that both groups had a significantly greater “good” than “bad” variance (p<0.05) for most of the swing phase, suggesting that mediolateral footpath is an important variable stabilized by the central nervous system during walking. Stroke subjects had significantly greater relative variance difference (ΔV) (i.e. normalized difference between “good” and “bad” variance) (p<0.05), indicating a stronger kinematic synergy in footpath stabilization, than the controls. In addition, the kinematic synergy in mediolateral footpath stabilization is strongest during mid-swing but weakest during late swing in healthy gait. However, this phase-dependent strategy is preserved for mid-swing but not for late swing in stroke gait. Moreover, stroke and healthy subjects demonstrated different relationships between UCM and walking stability measures. A stronger kinematic synergy in healthy gait is associated with better walking stability whereas having more “good variance” or stronger kinematic synergy in stroke gait is associated with less walking stability. The current findings suggest that walking with too much “good variance” in people following stroke, despite no effect on the footpath, may adversely affect their walking stability to some extent.
Highlights
Falls and fall-related injuries cause extremely costly health problems in stroke population [1]
There were significant main effects for group (F(1,112) = 15.74, η2 = 0.12, p
Inter-joint coordination to stabilize footpath following stroke good variance compared to the bad variance in the mediolateral footpath stabilization, indicating that mediolateral footpath during swing is an important task variable stabilized by the central nervous system (CNS)
Summary
Falls and fall-related injuries cause extremely costly health problems in stroke population [1]. Community-dwelling post-stroke individuals most often fall while walking [1, 2]. Inter-joint coordination to stabilize footpath following stroke shown that post-stroke individuals were more unstable especially in the frontal plane during walking such as having greater dynamic instability, increased trunk sways, and asymmetric foot placement in the mediolateral direction [3,4,5]. Post-stroke individuals had greater variability in spatiotemporal gait measures than neurologically intact controls [4, 6]. Stroke-related impairments such as reduced sensorimotor function, insufficient muscle strength and elevated reflex responses [7] may all contribute to the unstable walking patterns. The underlying mechanisms of increased walking instability and gait variability following stroke are not fully understood
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