Black, Christopher D, McCully, Kevin K · Dynamic medicine : DM · 2005 · DOI
This study tracked how much physical activity people with ME/CFS could do while following a walking program. Participants wore activity monitors for 4 weeks. They were able to meet their daily walking goals for the first 1-2 weeks, but then their activity levels dropped significantly and symptoms got worse, suggesting they had hit a limit their bodies could not sustain.
This study provides objective evidence of exercise intolerance in ME/CFS by documenting a specific time course of activity decline following initial capacity. Understanding when and how activity capacity fails is crucial for developing safe exercise protocols and recognizing post-exertional malaise, which is a hallmark feature of ME/CFS that distinguishes it from other conditions.
This study does not prove that exercise programs are harmful for all ME/CFS patients or that they should never be attempted. It also does not definitively establish the biological mechanisms underlying the observed activity decline. The small sample size and lack of detailed information about individual symptom tracking limit generalizability to broader populations.
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
Black, Christopher D & McCully, Kevin K (2005). Time course of exercise induced alterations in daily activity in chronic fatigue syndrome.. Dynamic medicine : DM. https://doi.org/10.1186/1476-5918-4-10
BibTeX
@article{mecfsatlas-black-2005-time-course,
author = {Black, Christopher D and McCully, Kevin K},
title = {Time course of exercise induced alterations in daily activity in chronic fatigue syndrome.},
journal = {Dynamic medicine : DM},
year = {2005},
doi = {10.1186/1476-5918-4-10},
note = {PubMed: 16255779},
url = {https://www.mecfsatlas.com/evidence/black-2005-time-course},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-26. https://www.mecfsatlas.com/evidence/black-2005-time-course
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