What is post-exertional malaise?

Even minor physical, cognitive or emotional activity can trigger PEM, which manifests itself with symptoms immediately or even 12-72 hours after a time delay.

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Post-exertional malaise describes a discomfort or a bad mood (malaise) that occurs after (post) exertion. Post-exertional malaise therefore describes a stress intolerance.

In those affected, existing symptoms can worsen or new symptoms can occur even after slight exertion. PEM is often accompanied by a sharp drop in performance and activity levels. Post-exertional malaise is sometimes referred to as a crash, which is comparable to the flu, a hangover or jet lag.

PEM is specific to ME/CFS. It is one of the clinical diagnostic criteria and leading symptoms of myalgic encephalomyelitis / chronic fatigue syndrome.

What are the triggers of post-exertional malaise?

Triggers for PEM can be very different. In principle, physical and cognitive activities, but also emotions, can be triggers. This includes activities and emotions that are negative and stressful, but also positive and joyful ones:

Everyday things can cause PEM:

  • shopping at the supermarket
  • going for a walk
  • Sitting or standing (orthostatic stress[add article])[2]
  • External stimuli such as light or noise
  • Mental effort such as reading, watching TV or a conversation

In ME/CFS patients, the severity of the underlying disease influences the triggers. The more severe the ME/CFS disease, the lower the threshold of the triggering activities and emotions.

PEM triggers can also change over the course of the disease. For example, one study showed that stress has a greater influence in the earlier stages of the disease than in patients who have suffered from ME/CFS for more than ten years [1].

What are symptoms of post-exertional malaise?

Common symptoms that occur with PEM include:

General symptoms

  • Exhaustion/severe fatigue
  • Flu-like symptoms (sore throat, muscle aches, increased fatigue)
  • Muscle weakness
  • Sleep problems/difficulty sleeping
  • Chills
  • Low grade fever
  • Drop in body temperature
  • Bladder dysfunction
  • *Cognitive symptoms
  • Brain fog (problems with concentration, information processing and memory)
  • Cognitive impairment


  • Physical pain
  • Headaches

Sensory symptoms

  • Increased sensitivity to noise, light, touch, vibration or movement

Fatigue is often the main symptom of PEM. However, it can also be accompanied by a worsening of existing symptoms and the appearance of new symptoms. The specific symptoms and their severity can vary from person to person. Symptoms can also fluctuate over time. PEM is characterised by the fact that these symptoms are triggered by minimal physical, cognitive or sensory effort that a healthy person would tolerate.

When does post-exertional malaise occur?

PEM can occur immediately after an activity or an emotional event, but also up to 12-72 hours later. One speaks of a latency or latent period of 12-72 hours. [1,5]

Some scientific studies have already addressed the issue of the latency period of PEM in patients with ME/CFS:

  • 11% of ME/CFS patients reported a persistent delay of at least 24 hours after the trigger before PEM symptoms appeared [4]
  • 84% of patients suffer from PEM 24 or more hours after exertion [4]
  • Physical exertion often leads to PEM after a shorter latency period than cognitive activities [1]

Due to the delayed temporal relationship between activity and PEM, it can be very difficult to identify triggers. Nevertheless, this is very important to avoid future crashes. One strategy for disease management is pacing.

How is post-exertional malaise diagnosed?

As PEMs can be associated with different triggers and varying symptoms, diagnosis is often very difficult.

Validated questionnaires that ask about the characteristics of PEM are often used to determine or objectify PEM. Frequently used questionnaires include

  • DePaul Symptom Questionnaire (DSQ) e.g. Does your fatigue worsen after minimal physical exertion and/or mental effort? If you feel worse after activity, how long does this last?
  • DePaul Post-Exertional Malaise Questionnaire (DPEMQ) Asks e.g. triggers of PEM, onset and duration of PEM symptoms, severity and type of symptoms occurring during PEM, effect of pacing on PEM [5]
  • Brief Questionnaire to Assess Post-Exertional Malaise This shortened 10-item questionnaire was derived from the DPEMQ. It records the frequency, severity and duration of PEM symptoms in the last 6 months.

In addition to validated questionnaires, physical tests can also be used.

  • The two-stage cardiopulmonary exercise test was used as an indicator of physical performance. As this test can lead to a permanent worsening of symptoms in ME/CFS patients, it is no longer usually used today.
  • The double hand force measurement can gently measure muscular fatigue. In the double hand force measurement, the hand force is measured ten times at intervals of one hour using a hand gripping device. In ME/CFS patients, hand strength decreases significantly in the second measurement [3,6]

The triggers, symptoms and effects of post-exertional malaise vary from patient to patient. However, PEM is characterised by a crash occurring after a low level of physical, cognitive or emotional activity, although the latency period may vary.

As there are currently no drug therapies available, PEM or crashes should be avoided, as each crash increases the risk of chronicity. One coping strategy is pacing, which enables those affected to re-learn their energy reserves and not exceed their limits.

[1] Hartle, M., Bateman, L., & Vernon, S.D. (2021). Dissecting the nature of post-exertional malaise. Fatigue: Biomedicine, Health & Behavior, 9 (1), 33—44. https://doi.org/10.1080/21641846.2021.1905415

[2] Campen et al (2021) Numeric Rating Scales Show Prolonged Post-exertional Symptoms After Orthostatic Testing of Adults With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Sec. Rheumatology Volume 7 - 2020. https://doi.org/10.3389/fmed.2020.602894

[3] Jaekel, B., Kedor, C., Grabowski, P. et al. Hand grip strength and fatigability: correlation with clinical parameters and diagnostic suitability in ME/CFS. J Transl Med 19, 159 (2021). https://doi.org/10.1186/s12967-021-02774-w

[4] Chu L, Valencia IJ, Garvert DW, Montoya JG (2018) Deconstructing post-exertional malaise in myalgic encephalomyelitis/ chronic fatigue syndrome: A patient-centered, cross-sectional survey. PLoS ONE 13 (6): e0197811. https://doi.org/10.1371/journal.pone.0197811[5] Jason LA, Holtzman CS, Sunnquist M, Cotler J. The development of an instrument to assess post-exertional malaise in patients with myalgic encephalomyelitis and chronic fatigue syndrome. J Health Psychol. 2021 Feb; 26 (2) :238-248. doi: 10.1177/1359105318805819. Epub 2018 Oct 24. PMID: 30354489; PMCID: PMC7988339.

[6] Hoffmann K, Hainzl A, Stingl M et al Interdisciplinary, Collaborative D-A-CH Consensus Statement on the Diagnosis and Treatment of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome [Interdisciplinary, Collaborative D-A-CH (Germany, Austria and Switzerland) Consensus Statement Concerning the Diagnostic and Treatment of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]. Vienna Klin Wochenschr. 2024 Aug; 136 (Suppl 5) :103-123. German. doi: 10.1007/s00508-024-02372-y. Epub 2024 May 14. PMID: 38743348; PMCID: PMC11093804.