What is Post Exertional Malaise (PEM)?


by Jeannie Di Bon, March 13th, 2024

What is Post Exertional Malaise (PEM)?

Estimated reading time: 3 minutes Post Exertional Malaise seems to be a hot topic right now. PEM is a cardinal symptom of ME/CFS. While fatigue is very common in my hypermobile patients, the fatigue experienced with ME/CFS can be different. I know, I have ME/CFS myself as do many of The Zebra Club members. I asked Emily Rich to explain more about PEM and how it may change the approach to exercise.

What are the symptoms of PEM

The most common symptoms of PEM include swollen lymph nodes, sore throat, muscle aches and pains, orthostatic intolerance, cognitive impairment, and disabling fatigue.

Is PEM the same as fatigue?

No. Fatigue is a general feeling of exhaustion and can come in many forms (see below). PEM however is a more whole-body, prolonged, and often delayed phenomenon. It is distinct because it is more comprehensive and significant. Fatigue, however, can occur with many different conditions and is not itself an indicator that exercise is counterproductive.

Is fatigue just physical?

No, fatigue can be a result of physical, cognitive, social, emotional, and sensory stimulation (among others).

Is PEM the same as Post Exercise Symptom Exacerbation (PESE)?

It depends on who you’re talking to. Both PEM and PESE are phrases that are sometimes used differently in different contexts. The concepts both generally refer to a worsening of symptoms that occur after exertion (physical, cognitive, emotional) that is out of proportion to the stimulus, meaning that we wouldn’t expect someone to be as symptomatic as they are considering what activity they just did.

This could include taking a shower (physical exertion) which leads to not being able to get out of bed for days. Reading a book (cognitive exertion) might lead to a person being unable to read for the rest of the day because of the onset of flu-like symptoms that are compounded by extreme, debilitating fatigue.

Typically, we talk about PEM in the context of it being a prolonged duration, and sometimes it is delayed, meaning someone may feel fine initially but the next day or 2 days later it “hits them.” This is not always the case, but it is important to distinguish PEM/PESE from an exertional fatigue during or immediately following an activity, which may be out of proportion for an otherwise healthy person, but for someone with exercise intolerance it is challenging.

For example, someone with POTS who has become deconditioned may experience feeling exhausted after a 5 or 10-minute recumbent cycle. It would not be surprising for that person to have palpitations, tachycardia, lightheadedness, etc. which are typical symptoms of POTS. However, we would expect that this person would be able to recover and wake up the next day with a fresh start, for the most part.

When I might suspect PEM is if that person continues to feel symptoms, especially fatigue and is overall unwell. This may even include some flu-like symptoms, swollen lymph nodes, and a sore throat. The word “crash” is commonly used to describe PEM and patients experience this prolonged, hangover type of feeling, which is differentiated from a POTS or pain flare.

PEM is a cardinal symptom of myalgic encephalomyelitis (ME/CFS), meaning that you have to have PEM to have ME/CFS. There is a physiological difference in the body’s processing of activity because it is a neuroimmune disease. We believe it is actually dangerous for these individuals to over-exert. That often leads to a worsening of function, which sometimes individuals do not recover from.

So, PEM is a defining feature of ME/CFS, however what is more controversial is whether someone having PEM means that they have ME/CFS or if this can exist (for example, in long-COVID) in the absence of ME/CFS.

It is very important to identify whether PEM is a factor in an individual’s specific body when determining a treatment plan. “Pushing through” in the case of PEM is counterproductive and will not lead to an increase in tolerance, in my clinical experience and from talking with many patients with ME/CFS.

However, in those with POTS, there is often a respectful level of discomfort that is expected with some level of exercise and we should see this decrease over time, with the right exercise program. In all cases, if a person is too tired to do their daily activities (bathing, dressing, walking, etc.) I would always prioritize those tasks first, over exercise. This must be done in collaboration with a skilled, knowledgeable professional.

Is ME/CFS the same as long-covid?

It depends on who you’re talking to. Generally speaking, no, as ME/CFS has specific criteria that must be met to make the diagnosis and many individuals with long-covid do not fit this criteria. However, many times, ME/CFS is triggered by an infection, and therefore we are seeing an uptick in cases of ME/CFS due to increased COVID infections over the last 4 years.

Emily Rich is a practicing occupational therapist, Ph.D candidate, and researcher. You can find her on Instagram or visit her website.  Emily also joined us for a blog on POTS and Exercise.

Jason et al, 2015 Problems in Defining Post-Exertional Malaise: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4295644/


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Patricia - 4th June 2024

Thank you so much for posting this. I was surprised to see Long Covid mentioned! As I am someone suffering from Long Covid, the minor acknowledgement means the world to me. I am still trying to navigate the difference of “normal fatigue” and PEM, to understand if I fall into the PEM diagnosis, or if it’s “normal fatigue”. It’s hard when you are someone who downplays symptoms and second guess yourself, then harder when discussing with doctors. This really helped give me a lot of information and a better understanding of PEM. Thank you so much! I wanted to share my appreciation for this.


    Jeannie Di Bon - 4th June 2024

    Thank you for taking the time to write and I am so glad this article resonated with you.


Lisa Reich - 23rd March 2024

Thank you for sharing this. I live this every day. I have been officially diagnosed with EDS , POTS and a long time ago CFS. I was an OT when I was able to work. The more professionals have this knowledge the less scary it will be for us to undergo therapy etc. It is terrifying when they dont understand and can truly devastate a person and set us back far.


    Jeannie Di Bon - 25th March 2024

    Thank you for sharing your experience. Yes, I do hope the more we talk about this, the more people will start to pay attention to PEM.