Post-Exertional Malaise

A Defining Symptom of Chronic Fatigue Syndrome

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Post-exertional malaise is the hallmark symptom of chronic fatigue syndrome. The brief definition is an inability to repeat previous exertion. However, that's a long way from providing a true understanding of this complex symptom of a complex disease.

To fully understand this term, first it's important to understand its component parts:

  • Malaise is a vague feeling of bodily discomfort or a general feeling of being unwell, much like you feel when you're coming down with a cold or the flu.
  • Post-exertional means occurring after exercise or another type of exertion. This can include cleaning house, shopping, or any other activity in which you expend energy.

In chronic fatigue syndrome, post-exertional malaise is a period of intense exhaustion and a spike in other symptoms that lasts for more than 24 hours following physical exertion, along with an inability to exercise as vigorously during that time. Some people say they experience it after mental exertion as well.

This symptom is a hallmark of the disease. Some research suggests that it may cause detectable differences in the blood, many of which are being studied as a possible diagnostic marker. It's also the basis of a suggested alternative name for chronic fatigue syndrome: systemic exercise intolerance disease, or SEID.

The term "malaise" is a fairly weak one to describe what people with this disease go through. Along with intense exhaustion, they may also have considerable muscle pain, cognitive dysfunction, and flu-like symptoms (sore throat, fever, etc.) In some, it may last for a day or two.

In others, it may last for a week or more.

The amount of exertion it takes to trigger this symptom varies greatly. In someone with a mild case, it might take an extra-long workout at the gym or a vacation that includes a lot of walking. In someone with a severe case, it could just take getting out of bed and showering.

Post-exertional malaise is often a source of considerable disability.

Some cases of fibromyalgia may involve a negative reaction to exercise as well. It's not yet clear whether this response is classifiable as post-exertional malaise.

Like chronic fatigue syndrome itself, the existence of post-exertional malaise is questioned by some medical professionals. However, we're learning more about its causes, which could help the symptom be taken more seriously as well as making better treatment available.


Lengert N, Drossel B. Biophysical chemistry. 2015 Jul;202:21-31. In silico analysis of exercise intolerance in myalgic encephalomyelitis/chronic fatigue syndrome.

Miller RR, et al. Journal of translational medicine. 2015 May 20;13:159. Submaximal exercise testing with near-infrared spectroscopy in myalgic encephalomyelitis/chronic fatigue syndrome patients compared to healthy controls: a case-controlled study.

Nijs J, Lundberg M. Clinical rheumatology. 2014 Jan;33(1):151-2. Avoidance behavior toward physical activity in chronic fatigue syndrome and fibromyalgia: the fear for post-exertional malaise.

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