Klaver-Krol, E G, Hermens, H J, Vermeulen, R C et al. · Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology · 2021 · DOI
Researchers used muscle sensors to measure how electrical signals travel through muscle fibers in people with ME/CFS, fibromyalgia, and healthy people during light strength exercises. They found that in ME/CFS patients, these electrical signals traveled unusually fast through muscle fibers as force increased, which didn't happen in the other groups. This suggests that muscle cells in ME/CFS may have a problem with how they work at the membrane level.
This study provides objective electrophysiological evidence of abnormal muscle fiber function specific to ME/CFS, helping distinguish it from fibromyalgia and supporting the biological basis of the disease. Understanding these underlying muscle membrane abnormalities may eventually lead to better diagnostic tools and targeted treatments for ME/CFS patients who currently lack objective biomarkers.
This study does not prove that abnormal muscle conduction velocity causes fatigue or muscle pain in ME/CFS—it only shows that the abnormality exists and correlates with the condition. The findings are limited to low-force contractions in females and cannot be generalized to males or to maximum-effort activities. It does not establish whether this membrane dysfunction is a primary cause of ME/CFS or a secondary consequence of the disease.
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
Klaver-Krol, E G, Hermens, H J, Vermeulen, R C, Klaver, M M, Luyten, H, Henriquez, N R, et al. (2021). Chronic fatigue syndrome: Abnormally fast muscle fiber conduction in the membranes of motor units at low static force load.. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology. https://doi.org/10.1016/j.clinph.2020.11.043
BibTeX
@article{mecfsatlas-klaver-krol-2021-chronic-fatigue,
author = {Klaver-Krol, E G and Hermens, H J and Vermeulen, R C and Klaver, M M and Luyten, H and Henriquez, N R and Zwarts, M J},
title = {Chronic fatigue syndrome: Abnormally fast muscle fiber conduction in the membranes of motor units at low static force load.},
journal = {Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology},
year = {2021},
doi = {10.1016/j.clinph.2020.11.043},
note = {PubMed: 33639451},
url = {https://www.mecfsatlas.com/evidence/klaver-krol-2021-chronic-fatigue},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/klaver-krol-2021-chronic-fatigue
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