Review Muscle strength, muscle endurance, voluntary activation, and perception of effort in ME/CFS: an overview, 2025, Nuzzo et al

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

Nuzzo, James L.; Taylor, Janet L.; Latella, Christopher

Abstract
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.

Web | Fatigue: Biomedicine, Health & Behavior
https://doi.org/10.1080/21641846.2025.2556941

 

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Another common symptom in ME/CFS is perceived muscle weakness. In one study, 45-75% of individuals with ME/CFS reported muscle weakness as a symptom. Yet, the extent to which muscle strength and endurance are objectively reduced in ME/CFS is unclear. Moreover, the extent to which muscle weakness in ME/CFS might be caused by muscle atrophy or reduced descending neural drive from the cortex and spinal motoneurons to the muscle (i.e. voluntary activation) is also unknown.

They seem a bit hung-up on the perceived nature, despite data showing an a tual reduction. I’m not sure how often this level of questioning of patients happens with other conditions

Most studies included individuals who met diagnostic criteria for ME/CFS based on one or more of the following sets of guidelines: Centers for Disease Control and Prevention (CDC) – Holmes et al], Oxford – Sharpe et al], CDC – Fukada et al. 1994, and Canadian Consensus Criteria (CCC) – Carruthers et al. (see Table 1). Some studies in the late 1980s and early 1990s used study-specific criteria for diagnosing ME/CFS or related syndromes. Two studies also included individuals who had chronic fatigue but did not meet criteria for ME/CFS. In these two studies, only muscle strength in individuals with chronic fatigue was compared to healthy controls and/or individuals diagnosed with ME/CFS. Disease duration was not consistently reported across papers

The huge range of different criteria for inclusion raises questions of course.

However when we get to the discussion there’s some good points raised

A reduction of 18.4% in muscle strength was found across various muscle groups and strength tests in individuals with ME/CFS compared to healthy controls. However, this reduction in strength is likely an underestimate of the true magnitude of strength loss from ME/CFS. The reason for this speculation is because condition severity appears to correlate with the magnitude of strength loss, and most individuals with ME/CFS who have been tested in laboratory studies have probably not been in a severe state when completing the strength tests

There’s lots of discussion of the differing results, the gist is covered in the abstract. Then this in the section on future research

The current overview reveals areas of research that could benefit from future exploration. First, relatively few individuals with ME/CFS have had their maximal muscle strength or endurance tested in research studies over the past 40 years. Thus, future testing of muscle strength and endurance in more individuals with ME/CFS will help clarify the extent to which these capacities are worsened by the condition. Also, individuals with severe or very severe ME/CFS (i.e. individuals who are bedbound or housebound) are probably not well represented in the literature on muscle strength and endurance. One way to reduce this sampling bias is for researchers to perform home-based testing

This just seemed weird. Getting people to do maximal endurance given PEM seems questionable IMHO. And while it’s good to look at including severely affected people in research I don’t see how doing endurance tests on with them is possible let alone ethical.

Overall it seems like a mixed bag. It’s a review which doesn’t really tell us a great deal I think given the huge range of criteria and methods.

Interesting to see this at the end

This research was supported by a grant awarded by ME Research UK

 

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They seem a bit hung-up on the perceived nature, despite data showing an a tual reduction.

I keep suggesting testing muscle performance with electrical stimulation, bypassing neural factors.