McCully, K K, Natelson, B H · Clinical science (London, England : 1979) · 1999
This study found that muscles in people with ME/CFS are not receiving oxygen as quickly and efficiently as they should after exercise or when blood flow is temporarily stopped. The researchers measured how fast oxygen returns to calf muscles and found it took significantly longer in ME/CFS patients compared to healthy people. They also found that the muscles' ability to use oxygen for energy was reduced by about 20% in ME/CFS patients.
This research provides objective physiological evidence for a specific mechanism underlying ME/CFS fatigue: impaired oxygen delivery to muscles. Understanding this mechanism could help clinicians better recognize ME/CFS, inform treatment approaches, and validate patient experiences of exertional limitation.
This study demonstrates that impaired oxygen delivery exists in ME/CFS but does not definitively prove it is the primary cause of fatigue, as correlation does not establish causation. The authors acknowledge they cannot distinguish whether reduced oxygen delivery is specific to ME/CFS or a secondary effect of reduced activity levels. The small sample size and cross-sectional design limit generalizability.
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
McCully, K K & Natelson, B H (1999). Impaired oxygen delivery to muscle in chronic fatigue syndrome.. Clinical science (London, England : 1979). https://pubmed.ncbi.nlm.nih.gov/10545311/
BibTeX
@article{mecfsatlas-mccully-1999-impaired-oxygen,
author = {McCully, K K and Natelson, B H},
title = {Impaired oxygen delivery to muscle in chronic fatigue syndrome.},
journal = {Clinical science (London, England : 1979)},
year = {1999},
note = {PubMed: 10545311},
url = {https://www.mecfsatlas.com/evidence/mccully-1999-impaired-oxygen},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-26. https://www.mecfsatlas.com/evidence/mccully-1999-impaired-oxygen
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