Muscle strength and power in persons with multiple sclerosis - A systematic review and meta-analysis

Multiple sclerosis (MS) is a chronic disease in the central nervous system which causes a number of physical symptoms including impairments of muscle mechanical function (muscle strength, muscle power and explosive muscle strength (~rate of force development, RFD)). However, a full overview of the existing knowledge regarding muscle mechanical function in persons with MS (PwMS) is still pending.

To systematically review 1) the psychometric properties of isokinetic dynamometry testing in PwMS, and 2) studies comparing muscle mechanical function in PwMS to matched healthy controls (HC). In addition, a meta-analysis will evaluate 3) the effects of progressive resistance training on muscle mechanical function in PwMS.

A systematic literature search was performed in eight databases. To be included in the review, the study had to 1) enroll participants with a confirmed diagnosis of MS; 2) assess muscle mechanical function 3) had undergone peer-review. The psychometric properties of isokinetic dynamometry were reviewed with respect to validity, reliability, and responsiveness. Comparison of muscle strength between PwMS and HC was performed across contraction velocities, contraction modes and muscle groups, as were the rate of force development. The effects of progressive resistance training on muscle mechanical function were evaluated in a meta-analysis using a random effects model and standardized mean difference (SMD).

A total of four, twenty-four, and ten studies were identified for aim 1, 2, and 3, respectively. High Intraclass correlations coefficients (range: 0.87-0.99) for isokinetic dynamometry was reported when assessing knee extensor and knee flexor muscle strength independent of contraction velocity. Compared to match HC, PwMS display impaired muscle strength, power and explosive muscle strength. Muscle strength impairments were most pronounced during maximal moderate to fast dynamic muscle contractions of the lower extremities. Progressive resistance training has a small but significant effect on muscle mechanical function in PwMS (SMD=0.45, 95% CI: 0.18-0.72, p=0.001).

The present review showed that 1) isokinetic dynamometry has a high reliability in PwMS; 2) muscle strength, power and rate of force development is impaired in PwMS compared to HC, and muscle strength impairments are most pronounced during maximal moderate to fast dynamic muscle contractions of the lower extremities; and 3) progressive resistance training can improve muscle mechanical function in PwMS. Future studies should evaluate progressive resistance training designed to optimize maximal moderate to fast dynamic muscle contractions of the lower extremities.