The role of muscle strength and voluntary activation on symptomatic fatigue in multiple sclerosis

This study investigated the role of muscle strength and voluntary activation (VA) on symptomatic fatigue in individuals with multiple sclerosis (MS). Nine women with relapsing- remitting or secondary-progressive MS (mean age, 43yrs) were compared to nine healthy women (mean age, 37yrs). Symptomatic fatigue was assessed using the Modified Fatigue Impact Scale (MFIS), Fatigue Severity Scale, and Visual Analogue Fatigue Scale. Functional capacity was assessed with a 6-Minute Walk Test (6-MWT). Muscle strength and VA were determined using twitch interpolation applied to the right dorsiflexor muscles during maximal voluntary isometric contractions (MVIC). Muscle fatigue was assessed during a sustained submaximal contraction. Distance during the 6-MWT, muscle strength and VA were significantly lower in the MS group. MFIS scores were negatively associated with muscle strength and VA. The MS group was more easily fatigued, as measured by MVIC. In conclusion, symptomatic fatigue is associated with muscle fatigue and weakness in individuals with MS