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Post Exertional Malaise

Post Exertional Malaise (PEM) is considered the hallmark characteristic of ME


Other terminology suggested includes “post exertional neuroimmune exhaustion” (PENE) or “post exertional symptom exacerbation” (PESE).

PEM is included as essential for diagnosis of ME in the IOM, ICC and Canadian criteria.

PEM is the additional symptoms and/or exacerbation of current symptoms in response to exertion

Key facts about PEM

  • Exertional trigger: physical, cognitive, sensory (touch, sound, smell) and/or emotional

  • Onset: tends to be delayed, on average 1-2 days after exertion

  • Duration: can last several days, or sometimes months or longer

  • Repeated triggering of PEM can lead to further deterioration in symptoms, therefore the aim is to avoid/minimise PEM.

How physiotherapy may trigger PEM

This applies to any physiotherapy intervention, whether for ME or an unrelated matter

PEM table.png

As PEM is often delayed, it may not be apparent in session. Always check on a person’s response to any intervention in the following 2-3 days to establish tolerance.


Assessment of PEM

Objective assessment

2-day Cardio-Pulmonary Exercise Test (CPET) (however the very nature of this will cause PEM and should be carefully clinically reasoned as to purpose with risks outlined)

The CPET has been used to trigger PEM for research purposes to study the physiological effects of physical exertion in people with ME. 


Subjective assessment

Look for patterns of exertional triggers followed by symptoms worsening

  • The person mentions “good days” of being able to do more, followed by “bad days”

  • Language such as “crash”, “payback”, “relapse”, “flare”

  • Needing the weekend to recover

  • Dropped usual activities just to manage basic daily living


Subjective outcome measure: DePaul symptom questionnaire

*Remember cognitive exertion from subjective questioning may trigger PEM. Consider timing, length and structure - gaining information in advance so a person can pace their replies is helpful


If physiotherapy is for an unrelated matter, the therapist must still understand the nature of that person's PEM and triggers in order to adapt treatment to minimise chance of causing PEM.

Physiotherapy management aims

  • Help to identify PEM triggers with careful analysis of activities and symptoms

  • Energy management strategies

  • Avoid/minimise triggering of PEM (particularly if treating an unrelated issue)

Currently there is no evidence for any effective physiotherapeutic interventions for people with ME when diagnostic criteria for participant selection includes PEM. This means:


  • Careful appraisal of current evidence base is required to determine if PEM is a criteria for participant selection, or if results cannot be generalised to people with ME

  • Future research needs to use diagnostic criteria that includes PEM as essential so that results can be applied to the ME population

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