Relationship between step length asymmetry and walking performance in subjects with chronic hemiparesis

Objective: To understand the relationship between step length asymmetry and hemiparetic walking performance. Design: Descriptive. Setting: Gait analysis laboratory. Participants: Convenience sample of 49 subjects with chronic hemiparesis. Interventions: Not applicable. Main Outcome Measures: Subjects walked at their self-selected walking speed over both an instrumented mat and forceplates to collect spatiotemporal parameters and ground reaction forces, respectively. Step length asymmetry was quantified by using a step length ratio (SLR) defined as paretic step length divided by nonparetic step length. Paretic leg propulsion, self-selected walking speed, hemiparetic severity (assessed by Brunnstrom stages of motor recovery), and some spatiotemporal walking parameters quantified the hermparetic walking performance. Paretic leg propulsion was quantified by the paretic propulsion (P-p) ratio, calculated as the percentage contribution of paretic leg to the total propulsive impulse. Results: Significant negative correlation (r=-.78) was revealed between SLR and P-p, indicating that subjects generating less propulsive force with the paretic leg walked asymmetrically with longer paretic steps than nonparetic steps. SLR and self-selected walking speed revealed a weaker correlation (r=-.35), whereas hemiparetic severity correlated strongly with SLR (rho=-.53). Conclusions: Step length asymmetry is related to propulsive force generation during hemiparetic walking. Subjects generating least paretic propulsion walk with relatively longer paretic steps. This suggests that one of the mechanisms for the longer paretic step may be the relatively greater compensatory nonparetic leg propulsion. Further, those with more severe hemiparesis (those dependent on abnormal flexor and extensor synergies) walk with the longest paretic steps relative to nonparetic. Finally, our results indicated that asymmetrical step lengths may not necessarily limit the self-selected walking speed, likely due to other compensatory mechanisms.