Lewis, S F, Haller, R G · Reviews of infectious diseases · 1991 · DOI
This review article explains how scientists measure exercise capacity and fatigue in the body. It describes three key concepts: aerobic fitness (how efficiently your heart and muscles use oxygen), muscle strength (your muscles' ability to produce force), and fatigue (the loss of strength that happens during activity). The authors discuss how these measurements might help us better understand what happens in ME/CFS when patients experience excessive fatigue.
Understanding the difference between weakness, fatigue, and reduced exercise capacity is fundamental to evaluating ME/CFS patients and avoiding potentially harmful exercise prescriptions. This framework helps clinicians and researchers measure exercise responses accurately and may clarify why post-exertional malaise occurs in ME/CFS. The paper provides a conceptual foundation for designing appropriate exercise testing protocols for this population.
This review does not provide new experimental evidence about ME/CFS pathophysiology or prove what causes fatigue in ME/CFS patients. It does not establish whether ME/CFS involves primary muscle dysfunction, cardiac limitations, or central nervous system factors. The paper does not demonstrate the effectiveness of any specific treatment or exercise intervention.
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
Lewis, S F & Haller, R G (1991). Physiologic measurement of exercise and fatigue with special reference to chronic fatigue syndrome.. Reviews of infectious diseases. https://doi.org/10.1093/clinids/13.supplement_1.s98
BibTeX
@article{mecfsatlas-lewis-1991-physiologic-measurement,
author = {Lewis, S F and Haller, R G},
title = {Physiologic measurement of exercise and fatigue with special reference to chronic fatigue syndrome.},
journal = {Reviews of infectious diseases},
year = {1991},
doi = {10.1093/clinids/13.supplement_1.s98},
note = {PubMed: 2020810},
url = {https://www.mecfsatlas.com/evidence/lewis-1991-physiologic-measurement},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/lewis-1991-physiologic-measurement
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