Effect of Contralateral Strength Training on Muscle Weakness in People With Multiple Sclerosis: Proof-of-Concept Case Series

Background. The contralateral strength training (CST) effect is a transfer of muscle performance to the untrained limb following training of the contralateral side. Objective. The aim of this study was to explore, in individuals with multiple sclerosis (MS) presenting marked lower limb strength asymmetry, the effectiveness of CST on management of muscle weakness of the more-affected limb following training of the less-affected limb. Design. A single-subject research design was used. Methods. Eight individuals with MS underwent 16 to 18 high-intensity training sessions of the less-affected ankle dorsiflexor muscles. The primary outcome measure of this single-system case series was maximal strength expressed as peak moment and maximal work. Secondary outcome measures were: Six-Minute-Walk Test, Timed Up & Go Test, 10-Meter Timed Walk Test, and Multiple Sclerosis Quality of Life-54 questionnaire. Results. After the 6-week intervention, the contralateral more affected (untrained) limb showed a 22% to 24% increase in maximal strength. From pretest-posttest measurements, participants also performed significantly better on the clinical and functional secondary outcome measures. At the 12-week follow-up, the strength levels of the weaker untrained limb remained significantly superior to baseline levels in the majority (5 out of 8) of the outcome parameters. Limitations. Considering the design used, the absence of a control group, and the sample size, these findings should be cautiously generalized and will need confirmation in a properly planned randomized controlled trial. Conclusions. The present proof-of-concept study shows, for the first time, the occurrence of the CST effect on muscle performance of ankle dorsiflexor muscles in people with MS. These preliminary findings reveal new potential implications for CST as a promising rehabilitation approach to those conditions where unilateral muscle weakness does not allow or makes difficult performing conventional strength training of the weaker limb.