E3 PreliminaryPreliminaryPEM requiredEditorialPeer-reviewedReviewed
Post-exertional malaise in daily life and experimental exercise models in patients with myalgic encephalomyelitis/chronic fatigue syndrome.
Vøllestad, Nina K, Mengshoel, Anne Marit · Frontiers in physiology · 2023 · DOI
Quick Summary
This paper reviews how post-exertional malaise (PEM)—the worsening of symptoms after physical or mental activity—is experienced and studied in ME/CFS patients. Patients describe PEM in many different ways and report that it can start immediately or be delayed by days, lasting anywhere from a few days to months. When researchers use standardized exercise tests in laboratories, they see more immediate symptom worsening, but the duration still varies widely between patients.
Why It Matters
Understanding how PEM actually manifests in patients' daily lives versus controlled research settings helps clinicians better recognize and validate patient experiences. This review identifies critical gaps in how PEM is studied and measured, which could lead to better diagnostic tools and more effective treatments tailored to the actual recovery processes that go wrong in ME/CFS.
Observed Findings
- Patients use highly variable language and concepts to describe their PEM experiences in everyday life
- PEM can have immediate onset or be delayed, with duration ranging from days to several months
- Standardized exercise tests trigger more immediate symptom exacerbation but with wide variability in recovery duration
- Evidence of altered muscular metabolism and autonomic nervous system responses when exercise is repeated on successive days
- Decreased muscular capacity persists for several days after controlled exercise bouts in ME/CFS patients
Inferred Conclusions
- The variability in how PEM presents between laboratory and daily life contexts suggests natural exertion triggers different responses than standardized tests
- The restitution (recovery) period following exertion is where PEM peaks and warrants greater research focus than the exercise period itself
- Altered muscular and autonomic responses to repeated exercise may explain why patients experience prolonged symptom worsening after activity
Remaining Questions
- What specific biological mechanisms in the restitution period cause PEM to peak, and why is recovery delayed in ME/CFS patients?
- Why is there such wide variability between patients in PEM onset timing and duration, both in daily life and experimental settings?
What This Study Does Not Prove
This perspective paper does not provide new experimental data proving the mechanisms causing PEM—it is a literature review and conceptual analysis. It does not establish which specific biological pathways (metabolic, autonomic, or other) are definitively responsible for PEM, only that altered responses occur during repeated exercise.
Tags
Symptom:Post-Exertional MalaiseFatigue
Biomarker:Metabolomics
Method Flag:PEM Not DefinedExploratory OnlyWeak Case Definition
Metadata
- DOI
- 10.3389/fphys.2023.1257557
- PMID
- 38111900
- Review status
- Editor reviewed
- Evidence level
- Early hypothesis, preprint, editorial, or weak support
- 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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