Lloyd, A R, Gandevia, S C, Hales, J P · Brain : a journal of neurology · 1991
Researchers tested whether ME/CFS patients have weak muscles or lack motivation during exercise compared to healthy people. They measured muscle strength and effort in both groups while performing repetitive arm exercises for 45 minutes. Both groups showed similar muscle performance and reported similar levels of effort, suggesting that muscle weakness or poor motivation are not the primary causes of fatigue in ME/CFS.
This study directly challenges common misconceptions that ME/CFS fatigue results from weak muscles or lack of effort—a stigmatizing assumption that has affected patient treatment and recognition. By demonstrating that muscle performance is normal during controlled exercise, it redirects attention toward central nervous system and metabolic mechanisms as the source of post-exertional malaise.
This study does not prove that central nervous system dysfunction causes ME/CFS fatigue, nor does it examine post-exertional malaise (delayed worsening after exercise). The single 45-minute exercise bout may not capture the mechanisms underlying delayed symptoms, and the findings apply specifically to isometric arm contractions in male subjects only.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Lloyd, A R, Gandevia, S C, & Hales, J P (1991). Muscle performance, voluntary activation, twitch properties and perceived effort in normal subjects and patients with the chronic fatigue syndrome.. Brain : a journal of neurology. https://pubmed.ncbi.nlm.nih.gov/1998892/
BibTeX
@article{mecfsatlas-lloyd-1991-muscle-performance,
author = {Lloyd, A R and Gandevia, S C and Hales, J P},
title = {Muscle performance, voluntary activation, twitch properties and perceived effort in normal subjects and patients with the chronic fatigue syndrome.},
journal = {Brain : a journal of neurology},
year = {1991},
note = {PubMed: 1998892},
url = {https://www.mecfsatlas.com/evidence/lloyd-1991-muscle-performance},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-29. https://www.mecfsatlas.com/evidence/lloyd-1991-muscle-performance
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