Does disability level impact the relationship of muscle strength to walking performance in people with multiple sclerosis? a cross-sectional analysis

Background and Purpose: Strength training can improve muscle weakness in people with multiple sclerosis (MS), but does not consistently improve walking. Disability level may impact the relationship of muscle weakness and walking performance in people with MS, but few studies have investigated the impact of disability on the re- lationship of strength and walking. The purpose of this study was to compare the relationships of strength in lower body and trunk muscles to walking performance between mild and moderate disability groups in people with MS. Methods: Data from 36 participants with MS who had mild disability (Expanded Disability Status Scale - EDSS 0 to 3.5) and 36 participants who had moderate disability (EDSS 4.0 to 5.5) were analyzed. Hand-held dyna- mometry measured strength in eight muscle groups from the ankle, knee, hip, and trunk. Timed 25 -Foot Walk (T25FW) and 6 -Minute Walk Test (6MWT) measured walking speed and endurance, respectively. Pearson cor- relations and beta coefficients (Delta beta) were reported for each bivariate relationship of muscle strength to T25FW and 6MWT from both mild and moderate disability groups. Linear regression was then used to compare differences in beta coefficients (Delta beta) between disability groups for the relationship of each muscle variable to T25FW and 6MWT. A positive Delta beta indicated a stronger relationship of strength to walking performance in the mild disability group, while a negative Delta beta favored the moderate disability group. Results: Overall, there were stronger Pearson correlations between muscle strength variables to T25FW and 6MWT in the mild ( r = 0.57 to 0.77) compared to moderate disability group ( r = 0.10 to 0.54). The mild disability group had significantly greater beta coefficients for T25FW with ankle dorsiflexion (Delta beta = 0.67, 95%CI: 0.27-1.07), knee extension (Delta beta = 0.68, 95%CI: 0.28-1.08), and hip abduction (Delta beta = 0.77, 95%CI: 0.01-1.52); and for 6MWT with knee extension (Delta beta = 0.47, 95%CI: 0.06 to 0.88). Discussion and Conclusion: For people with MS, muscle strength in the lower extremity and trunk may be a more important contributor to T25FW in mild versus moderate disability, but not for 6MWT. While more studies are needed, these results may help to inform rehabilitation intervention when prioritizing strength training to im- prove walking.