PEM can affect you even if the exertion is minor.
With PEM, symptoms typically worsen 12 to 48 hours after activity.
What Is Post-Exertional Malaise?
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People with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CSF) experience a worsening of symptoms after exercise or mental exertion.
The presence of post-exertional malaise is one of the key differences between ME/CSF and other conditions that cause fatigue.
PEM substantially limits the activity levels of people with ME/CFS and considerably lowers their quality of life.
In severe cases, PEM can define a person’s entire life.
Many healthcare providers consider PEM to be a key to diagnosing ME/CFS.
People with ME/CFS say post-exertional malaise feels like a “crash” or a “collapse.”
PEM can range from moderately stronger-than-normal symptoms to completely disabling.
In a mild case, a person may have extra fatigue, achiness, and cognitive dysfunction.
The range of PEM symptoms can include:
What Triggers Post-Exertional Malaise?
Post-exertional malaise is triggered by exercise or mental exertion.
The exertion needed to trigger PEM is different for everyone.
Triggering activities don’t necessarily need to be strenuous.
Mental activities that require concentration or mental calculation can also trigger PEM.
Even treatment that isn’t aimed at PEM specifically may help reduce its severity.
Preventing Post-Exertional Malaise
If you have ME/CFS, it’s important to understand your limits and triggers.
If your ME/CFS symptoms improve, talk to your healthcare provider about increasing your activities.
They will likely suggest slow, closely monitored increases in both physical and mental activities.
Exercise may be helpful for some people but not for others.
Don’t attempt to add exercise to your routine without first talking to your healthcare provider.
This may be in part because ME/CFS itself is a controversial diagnosis.
This further complicates the understanding of PEM.
Current diagnostic criteria require symptoms lasting at least six months.
This can lead to a significant decrease in activity and physical deconditioning.
Many people wait much longer than six months for a diagnosis, however.
The research in this area is somewhat mixed.
Summary
PEM describes a worsening of the symptoms of chronic fatigue syndrome.
It is triggered by mental or physical exertion.
Symptoms can include severe brain fog, flu-like symptoms, pain, and weakness.
It’s better to prevent PEM than it is to treat it once it happens.
Try keeping a journal of activities and symptoms so you will understand your activity limits.
Talk to your healthcare provider before adding exercise to your routine.
Centers for Disease Control and Prevention.Strategies to prevent worsening of symptoms.
Spotila JM.Post-exertional malaise: Perception and reality.
What’s in a name?
Systemic exertion intolerance disease.The Lancet.
2015;385(9969):663. doi:10.1016/S0140-6736(15)60270-7
Johns Hopkins Medicine.What is post-exertional malaise?
Friedman KJ.Advances in ME/CFS: Past, present, and future.Front Pediatr.
2023;60(1):83.
2015;79(6):537-49. doi:10.1016/j.jpsychores.2015.08.008
