Keller, Betsy A, Pryor, John Luke, Giloteaux, Ludovic · Journal of translational medicine · 2014 · DOI
This study tested whether people with ME/CFS can perform the same on an exercise test when it's repeated the next day, similar to how healthy people typically do. The researchers found that ME/CFS patients performed significantly worse on the second test—using about 14% less oxygen and doing about 12% less work—even though they were trying their hardest both times. This suggests that doing one exercise test may give doctors an unrealistic picture of what ME/CFS patients can actually do.
This finding could improve ME/CFS diagnosis by identifying a distinctive physiological marker—the inability to reproduce exercise performance—that differentiates ME/CFS from other conditions. It also demonstrates that single exercise tests underestimate disability in ME/CFS, which has important implications for clinical assessment, disability evaluation, and prescribing safe activity levels for patients.
This study does not establish what biological mechanisms cause the performance drop (whether mitochondrial dysfunction, autonomic dysregulation, or another cause). It also does not prove that repeat testing should replace other diagnostic criteria, as the small sample size and lack of blinded controls limit generalizability. Correlation between test variability and ME/CFS diagnosis does not prove causation of the underlying illness.
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
Keller, Betsy A, Pryor, John Luke, & Giloteaux, Ludovic (2014). Inability of myalgic encephalomyelitis/chronic fatigue syndrome patients to reproduce VO₂peak indicates functional impairment.. Journal of translational medicine. https://doi.org/10.1186/1479-5876-12-104
BibTeX
@article{mecfsatlas-keller-2014-inability-myalgic,
author = {Keller, Betsy A and Pryor, John Luke and Giloteaux, Ludovic},
title = {Inability of myalgic encephalomyelitis/chronic fatigue syndrome patients to reproduce VO₂peak indicates functional impairment.},
journal = {Journal of translational medicine},
year = {2014},
doi = {10.1186/1479-5876-12-104},
note = {PubMed: 24755065},
url = {https://www.mecfsatlas.com/evidence/keller-2014-inability-myalgic},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-26. https://www.mecfsatlas.com/evidence/keller-2014-inability-myalgic
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