Isokinetic predictors of gait speed increase following high-intensity resistance training of the ankle dorsiflexors in people with multiple sclerosis: A pilot study

Background: Maximal strength is a predictor of functional capacity for people with multiple sclerosis (PwMS), who frequently exhibit unilateral weakness of the ankle dorsiflexors. Aims of this study were to investigate the relationships between dorsiflexors' weakness and gait speed, the effects of high-intensity training of the affected dorsiflexors on gait performance and to identify isokinetic predictors of changes in gait speed in PwMs. Methods: Twenty patients aged 45 (10.3) years, illness duration 14.9 (8.5) years, median EDSS 3, underwent isokinetic dorsiflexors' strength testing at 10 degrees/s and 45 degrees/s angular velocities and gait analysis before and after a 6-week training of dorsiflexors. Pre-to-post differences in strength and gait parameters were analyzed by paired t-test; association between gait speed and isokinetic parameters was tested through correlation and regression analyses. Findings: Dorsifiexors' strength (peak moment at 10 degrees/s: +14.9%, p = 0.02; at 45 degrees/s: + 21.7%, p = 0.03) and gait parameters (speed: + 9.6%; p = 0.004; stride time: 5.7%; p = 0.01; cadence: +6.2%; p = 0.001; ankle power: +27.5%, p = 0.003) increased significantly. Of the thirteen isokinetic descriptors of strength, only peak moment, maximal and total work significantly correlated with gait speed increase. Regression analyses revealed high beta coefficients only for maximal work (10 degrees/s: B = 6.528; beta = 1.825; p = 0.008; 45 degrees/s: B = 1.466; beta = 1.364; p = 0.03). Interpretation: In PwMS, high-intensity training of weakened ankle dorsiflexors induced significant improvements in maximal strength and gait speed. The finding of maximal work as a significant predictor of training-induced changes in gait speed suggests that PwMS with reduced muscle work may benefit from strength training approaches aimed at increasing gait speed.