Different Biomechanical Variables Explain Within-Subjects Versus Between-Subjects Variance in Step Length Asymmetry Post-Stroke.

Natalia Sanchez,James M Finley,Nicolas Schweighofer

doi:10.1109/tnsre.2021.3090324

Abstract

Step length asymmetry (SLA) is common in most stroke survivors. Several studies have shown that factors such as paretic propulsion can explain between-subjects differences in SLA. However, whether the factors that account for between-subjects variance in SLA are consistent with those that account for within-subjects, stride-by-stride variance in SLA has not been determined. SLA direction is heterogeneous, and different impairments likely contribute to differences in SLA direction. Here, we identified common predictors between-subjects that explain within-subjects variance in SLA using sparse partial least squares regression (sPLSR). We determined whether the SLA predictors differ based on SLA direction and whether predictors obtained from within-subjects analyses were the same as those obtained from between-subjects analyses. We found that for participants who walked with longer paretic steps paretic double support time, braking impulse, peak vertical ground reaction force, and peak plantarflexion moment explained 59% of the within-subjects variance in SLA. However the within-subjects variance accounted for by each individual predictor was less than 10%. Peak paretic plantarflexion moment accounted for 4% of the within-subjects variance and 42% of the between-subjects variance in SLA. In participants who walked with shorter paretic steps, paretic and non-paretic braking impulse explained 18% of the within-subjects variance in SLA. Conversely, paretic braking impulse explained 68% of the between-subjects variance in SLA, but the association between SLA and paretic braking impulse was in the opposite direction for within-subjects vs. between-subjects analyses. Thus, the relationships that explain between-subjects variance might not account for within-subjects stride-by-stride variance in SLA.

Highlights

G AIT impairment is common in the majority of survivors of stroke
We accumulated a total of 371 strides, and |step length asymmetry (SLA)| was normally distributed with an average magnitude of 71 ± 40 mm
We found that the factors that account for within-subjects variance in |SLA| depend on the direction of asymmetry

Summary

Introduction

G AIT impairment is common in the majority of survivors of stroke. A common measure of gait impairment post-stroke is step length asymmetry (SLA). Studies assessing factors associated with SLA post-stroke rely on average measures obtained over multiple strides for each participant, and use techniques such as univariate correlation [8]–[10], analysis of variance [9], [11], [12], or linear regression [8], [13], [14] to understand factors that explain between-subjects differences in SLA These studies have identified factors related to forward propulsion, such as paretic propulsion [10], [15], [16], plantarflexion moments [9], and trailing limb extension [17], as primary correlates of SLA. Whether these between-subjects relationships hold at a within-subjects level remains to be determined

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