Relationship Between Muscle Strength Parameters and Functional Capacity in Persons with Mild to Moderate Degree Multiple Sclerosis

Background: Maximal muscle strength has been shown to be an important predictor of functional capacity for persons with multiple sclerosis (PwMS). Another muscle strength parameter known to be important for functional capacity in other patient groups is rate of force development (RFD) in knee extensors and flexors. This has not been investigated for PwMS. Thus, the purpose of this study was to investigate the relationship between RFD and maximal muscle strength of knee extensors and flexors and measures of functional capacity in PwMS.

Methods: 35 PwMS (Expanded Disability Status Scale 2-4) underwent isokinetic dynamometry to determine RFD and maximal isometric and isokinetic muscle strength for both legs. Furthermore all participants performed timed 25 foot walk tests (T25FWT), two minute walk tests (2MWT), stairclimb tests and 5-time sit-to-stand (5STS) tests to determine functional capacity. Multiple linear regressions were performed to determine which muscle strength parameter would serve as a stronger predictor of walking performance.

Results: Both RFD and maximal muscle strength correlated with functional capacity. Correlations were strongest for knee extensors and flexors of the weaker leg, while no clear ranking of the influence of the knee extensors vs. flexors on walking was evident. Multiple linear regressions showed that maximal isokinetic strength of the weaker leg is a better predictor for T25FWT and 2MWT performance than RFD.

Conclusions: Maximal muscle strength of the weaker leg is the better predictor of walking performance in persons with mild to moderate multiple sclerosis. RFD, although also important for functional capacity, is a less strong predictor. Maximal strength of the knee extensors, rather than the knee flexors, predicted performance in the stairclimb and 5STS tests.