Effect of progressive horizontal resistive force on the comfortable walking speed of individuals post-stroke

Background: Individuals post-stroke select slow comfortable walking speeds (CWS) and the major factors used to select their CWS is unknown. Objective: To determine the extent to which slow CWS post-stroke is achieved through matching a relative force output or targeting a particular walking speed. Methods: Ten neurologically nonimpaired individuals and fourteen chronic stroke survivors with hemiplegia were recruited. Participants were instructed to "walk at the speed that feels most comfortable" on a treadmill against 12 progressively increasing horizontal resistive force levels applied at the pelvis using a robotic system that allowed participant to self-select their walking speed. We compared slope coefficients of the simple linear regressions between the observed normalized force vs. normalized speed relationship in each group to a slope of-1.0 (i.e. ideal slope for a constant relative force output) and 0.0 (i.e. ideal slope for a constant relative speed). We also compared slope coefficients between groups. Results: The slope coefficients were significantly greater than-1.0 (p < 0.001 for both) and significantly less than 0 (p < 0.001 for both). However, compared with nonimpaired individuals, people post-stroke were less able to maintain their walking speed (p = 0.003). Conclusions: The results of this study provide evidence for a complex interaction between the regulation of relative force output and intention to move at a particular speed in the selection of the CWS for individuals post-stroke. This would suggest that therapeutic interventions should not only focus on task specific lower-limb strengthening exercises (e.g. walking against resistance), but should also focus on increasing the range of speeds at which people can safely walk.