Nijs, Jo, Meeus, Mira, McGregor, Neil R et al. · Medicine and science in sports and exercise · 2005 · DOI
This study looked at whether problems with the immune system might explain why people with ME/CFS feel exhausted after exercise and cannot exercise as much as healthy people. Researchers tested 16 ME/CFS patients' immune cells and had them exercise on a stationary bike while measuring their oxygen use and heart rate. They found that two specific immune markers—elastase and protein kinase R—were linked to reduced exercise capacity, suggesting immune dysfunction may play a role in abnormal exercise responses.
This study provides empirical evidence that ME/CFS exercise intolerance may have a biological basis in immune dysfunction, rather than being purely psychological. If confirmed, identifying specific immune markers could help explain postexertional malaise and eventually lead to targeted treatments or better diagnostic criteria for ME/CFS.
This small cross-sectional study cannot prove that immune dysfunction causes reduced exercise capacity—it only shows associations and correlations. The study lacks a healthy control group, so we cannot determine whether these immune markers are abnormal in CFS or simply associated with any reduction in fitness. The authors explicitly state that prospective longitudinal studies are needed to establish causation.
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
Nijs, Jo, Meeus, Mira, McGregor, Neil R, Meeusen, Romain, de Schutter, Guy, van Hoof, Elke, et al. (2005). Chronic fatigue syndrome: exercise performance related to immune dysfunction.. Medicine and science in sports and exercise. https://doi.org/10.1249/01.mss.0000181680.35503.ce
BibTeX
@article{mecfsatlas-nijs-2005-chronic-fatigue,
author = {Nijs, Jo and Meeus, Mira and McGregor, Neil R and Meeusen, Romain and de Schutter, Guy and van Hoof, Elke and de Meirleir, Kenny},
title = {Chronic fatigue syndrome: exercise performance related to immune dysfunction.},
journal = {Medicine and science in sports and exercise},
year = {2005},
doi = {10.1249/01.mss.0000181680.35503.ce},
note = {PubMed: 16260962},
url = {https://www.mecfsatlas.com/evidence/nijs-2005-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/nijs-2005-chronic-fatigue
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