E2 ModerateModerate confidencePEM requiredCross-SectionalPeer-reviewedReviewed
Comparing Idiopathic Chronic Fatigue and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) in Males: Response to Two-Day Cardiopulmonary Exercise Testing Protocol.
van Campen, C Linda M C, Visser, Frans C · Healthcare (Basel, Switzerland) · 2021 · DOI
Quick Summary
This study compared how men with ME/CFS respond to exercise testing on two consecutive days versus men with chronic fatigue that doesn't meet ME/CFS criteria. When ME/CFS patients exercised on the second day, they performed worse and couldn't reach the same levels they achieved on day one. Men with chronic fatigue (but not ME/CFS) actually improved on day two, similar to healthy people.
Why It Matters
This study provides objective physiological evidence that ME/CFS produces a characteristic abnormal response to exercise (post-exertional malaise) that distinguishes it from other forms of chronic fatigue. The two-day CPET protocol may serve as a useful biomarker to help clinicians differentiate between ME/CFS and other fatigue conditions, improving diagnostic accuracy and potentially guiding treatment decisions.
Observed Findings
- ME/CFS patients showed significant decline in oxygen consumption and workload from CPET1 to CPET2
- ICF patients showed improved performance on CPET2, similar to sedentary controls
- Resting heart rate and respiratory exchange ratio did not differ significantly between the two testing days in either group
- All other CPET parameters at ventilatory threshold and maximum exercise differed significantly between groups (p-values 0.002 to <0.0001)
- Seven ME/CFS patients had fibromyalgia compared to zero ICF patients
Inferred Conclusions
- Male ME/CFS patients demonstrate exercise intolerance characterized by deteriorating performance on a second consecutive day of testing
- This two-day CPET response pattern appears specific to ME/CFS and may help distinguish it from other forms of chronic fatigue
- The abnormal response to repeated exercise in ME/CFS aligns with published findings in male ME/CFS populations and supports the biological distinctiveness of the condition
Remaining Questions
- Does this two-day CPET response pattern differ in female ME/CFS patients, who comprise the majority of the patient population?
- What physiological mechanisms underlie the deterioration in exercise performance observed on day 2 in ME/CFS patients?
What This Study Does Not Prove
This study does not prove that the two-day CPET can be used routinely in clinical practice—it was conducted in a research setting with relatively small numbers. It does not establish why ME/CFS patients show this deterioration pattern, only that they do. Results are limited to males and may not apply to female ME/CFS patients, who represent the majority of the ME/CFS population.
Tags
Symptom:Post-Exertional MalaiseFatigue
Method Flag:Strong PhenotypingSex-StratifiedWeak Case DefinitionSmall SampleMixed Cohort
Biomarker:Blood Biomarker
Metadata
- DOI
- 10.3390/healthcare9060683
- PMID
- 34198946
- Review status
- Editor reviewed
- Evidence level
- Single-study or moderate support from human research
- Last updated
- 12 April 2026
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 →
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