Muscle strength, muscle endurance, voluntary activation, and perception of effort in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS): an overview

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating condition characterized by fatigue, post-exertional malaise, perceived muscle weakness and other symptoms. Whether muscle strength is objectively reduced in ME/CFS is unclear. Objective and methods: Our aim was to determine if muscle strength, muscle endurance, voluntary activation, and perceived effort during muscle endurance tasks are altered in ME/CFS by reviewing the relevant literature. Results: We identified 27 studies that compared muscle strength or endurance between individuals with ME/CFS (n = 1,023) and healthy controls (n = 672). Tests typically involved handgrip, elbow flexion, or knee extension tasks. Across studies, muscle strength and muscle endurance were 18.4 ± 12.9% and 10.9 ± 26.7% lower, respectively, in individuals with ME/CFS compared to healthy controls. Results from six studies did not clearly indicate if poorer strength was due to reduced voluntary activation, and no comparative studies related these outcomes to whole muscle atrophy. Three studies indicated that individuals with ME/CFS report greater perceived effort during muscle endurance tests than healthy controls. Conclusions: Individuals with ME/CFS exhibit reduced muscle strength, reduced muscle endurance, and heightened perceptions of effort during muscle endurance tasks than healthy controls.