The experience of post-exertional malaise – part 2

This is the second of a two-part series discussing research from 2020 by Barbara Stussman and colleagues exploring the experiences of post-exertional malaise (PEM) in 43 individuals who reported having ME/CFS.

Read part one of this article for an overview of the study.

Triggers of PEM

Physical triggers

The study revealed that even seemingly minimal physical activities could trigger PEM. Whilst more obvious examples are given such as riding a bike and attending a concert, triggers that may not be considered by someone without prior knowledge of ME/CFS are included, such as vacation, gentle yoga, walking and driving.

One participant described their experience of grocery shopping:

“I can go grocery shopping 1 day and I am completely spent for 2 or 3 days.”

Cognitive triggers

Everyday cognitive activities like reading or engaging in conversations could induce worsening fatigue, cognitive dysfunction, and a myriad of other symptoms, as illustrated by participants’ experiences:

“I specifically notice it if I’ve had a one-on-one conversation with a friend. After about anywhere from 30 min to an hour, my brain literally starts to shut down, and I can’t think clearly and I can’t pay attention anymore.”

Emotional triggers

Emotional stress emerged as another significant trigger for PEM, as detailed by a participant’s experience following increased social interaction:

“Compared to a normal Saturday for me, which is just having my son at home with my husband, I engaged in several hours of social interaction, which I normally don’t do. I have all this extra stress of parents coming. It’s unexpected and other people in my house and all of that. So the next day midmorning, I start feeling bad and I know I definitely need to rest. So I start feeling bad and I lay down. I am basically in bed for 4 hours.”

Importance of assessing baseline

Participants emphasised the significance of understanding their baseline symptoms, as exertion during heightened symptom periods could compound the effects of PEM, amplifying symptoms. A participant described this compounding effect, noting that they were unable to do a regular task like getting in the car to pick up their children because attending a doctor appointment 2 days previously had exacerbated their baseline.

This compounding effect is of particular concern in relation to cardiopulmonary exercise testing (CPET), where travel to the testing site may itself trigger PEM. Therefore, an accurate baseline assessment before CPET becomes crucial. One participant discussed the impact of travel prior to CPET:

“I had to travel several days across a number of states and I had to fly and all that, so it took a lot out of me just to get to the site of the testing, so I was feeling worse than a typical day for me by the time I got to the test site.”


Both daily PEM and PEM following CPET were reported to have similar sets of symptoms, with certain participants describing the latter as more intense. Three core symptoms – exhaustion, cognitive difficulties and neuromuscular complaints – were consistently reported, but participants also detailed a broad range of manifestations, including sensory sensitivity, feelings of despair, difficulty sleeping, headaches, nausea, and sore throat. As stated in the paper, PEM symptoms were very specific to each individual.

The exhaustion experienced during PEM surpassed typical post-activity fatigue, resembling the prolonged fatigue seen in flu but lasting for years, as described by one participant. Another participant vividly expressed the profound exhaustion following CPET, requiring assistance to move from the exercise bike to a nearby bed.

Cognitive difficulties were characterised by issues with thinking, decision-making and word recall, with one individual describing it as being in a “complete fog” for days. Neuromuscular complaints included muscle pain/aches and weakness, affecting routine tasks such as a short visit to a local store, leaving legs shaky and requiring extended rest.


Regarding timeframes for symptom onset, PEM following CPET was generally observed to be more immediate and longer in duration compared with PEM in daily life. According to the study, “for daily PEM, most participants perceived a delayed onset of symptoms, with nearly half reporting symptoms beginning 12–48 h after exertion. In contrast, more than three-quarters of participants reporting the onset of symptoms following CPET said they began immediately or within several hours.”

Furthermore, the peak intensity of PEM symptoms occurred earlier (around 24 hours post-exertion) for those undergoing CPET, whereas daily life-related PEM symptoms tended to peak at around 48 hours post-exertion. One participant emphasised the stark difference in energy expenditure during CPET compared to everyday life, highlighting the rapid and intense energy depletion during the testing process:

“It was radically different than what normal life is because a lot of energy was expended in a short period of time… My day to day life is much different than that. I don’t normally use energy that quickly and in that quantity. It’s usually more of a gradual pronounced thing, whether it’s working around the house a little bit, doing different chores… Normally that buildup of energy happens over a longer period of time.”

Relief from PEM

According to the researchers, virtually every participant agreed that complete rest was necessary to reduce PEM symptoms. Most participants agreed that this involved lying down “absolutely flat” with minimal sensory input. Importantly, many participants stressed that complete rest was not merely a strategic choice rather it was a “demand from the body”, as one participant expressed:

“Complete rest is really the only thing that can facilitate a recovery for me. Basically, I have to stop and put things on hold because I realize when I am weakened with PEM, if I push through… I will end up making the symptoms worse, like going downhill really fast.”

One participant who underwent CPET described how she still had not fully recovered from PEM:

“By the time I got home, I was pretty much a wreck. I was able to walk into the house on my own with my husband helping hold me up but I was unable to function at all. I wasn’t brushing my teeth. I was just focused on getting to the bathroom. And I would say it took 4 months before I came back to close to my baseline. I don’t think I’ve ever returned back to what I was before I walked into that test.”

Participants did employ strategies in order to avoid PEM, considering planning and moderation of energy expenditure (i.e. pacing) as essential. Helpful strategies included resting more than was needed and calendar management (shifting activities around to depending on the amount of required energy predicted). However, pacing was not without its consequences, as one participant described missing major life events such as weddings.

Uncertainty in relation to PEM

The reported durations of PEM varied among participants, contributing to the overall uncertainty surrounding this feature of ME/CFS. Participants described the anxiety of not knowing how long a PEM episode would last or whether they would return to their baseline (pre-PEM). There was also uncertainty around identifying triggers of PEM, as expressed by one participant:

“It seems unpredictable in my case because I could do the same thing two different days, and one day it affects me a lot more than the other day.”


This qualitative study stands as a crucial contribution to ME/CFS research, offering deeper insights into the nuanced experience of PEM in daily life and following CPET. While commonalities exist in the PEM experiences across individuals, the study underscores the unique experience of PEM for each individual.

According  to the researchers, “The current study is the first in the available literature using qualitative methods to compare daily PEM and PEM following CPET evaluation.” The results highlight that PEM following CPET is potentially more immediate, intense and longer in duration than PEM in daily life, albeit with variations within both groups.

The study findings also highlight the need for researchers to be aware of the triggers of PEM prior to CPET, including travel to the testing site. Given the nature and intensity of CPET, the study demonstrate the need for appropriate after-care for participants. Furthermore, it is vital that fully informed consent is given, whereby each participant is aware of the risks of participating and feels comfortable to withdraw their consent at any point.


This qualitative study is a valuable complement to quantitative research, although certain limitations need consideration. Out of a potential 247 individuals, only 43 were selected to participate. The rationale for participant selection was to “maximise variability” across various demographic factors, yet a more detailed explanation of the exclusion process could enhance transparency.

Participants are described as individuals who “reported a medical diagnosis of ME/CFS and had a physician refer them for ME/CFS specific CPET testing in the community” and no attempt was made by the researchers to understand whether participants would fulfil a criteria-based diagnosis such as according to the Canadian Consensus Criteria(CCC). The absence of confirmation of ME/CFS diagnoses raises questions about the broader applicability of the study findings, and highlights an avenue for potential refinement in future research.

Furthermore, there was reliance on retrospective recall within the study which could influence the accuracy and completeness of information gathered.

Read more about predicting the severity of PEM

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