How to Reverse PEM for Good (ME/CFS Recovery)

Can PEM Be Reversed for Good?

NICE states that no therapy based on physical activity or exercise is effective as a cure for ME/CFS (NICE, 2021), and nobody can promise that PEM will go away for any one person. The practical goal is a wider window of what you can do before a crash. Our team measures that window at the start and again as it changes, so you can see whether it's widening in your body.

What Is a PEM Crash?

Post-exertional malaise (PEM) is a worsening of some or all of your symptoms after physical or mental effort, or after time upright, that leaves you able to do less (IOM, 2015). It's 1 of the 3 symptoms required under the 2015 IOM diagnostic criteria for ME/CFS, along with a lasting drop in what you can do and sleep that doesn't refresh you, plus either trouble thinking or orthostatic intolerance (IOM, 2015). A PEM crash is that worsening: the stretch, from hours to months, when symptoms flare after an effort. Several of the studies below used older definitions of ME/CFS or chronic fatigue syndrome that didn't require PEM, so some people in those groups may not have had it.

A crash brings fatigue and a whole set of other symptoms. After a single maximal exercise test, women with chronic fatigue syndrome reported fatigue, lightheadedness, muscle and joint pain, trouble thinking, headache, nausea, weakness, shakiness, poor sleep and a sore throat or glands (VanNess, 2010).

A crash can feel like proof that effort damages you, which makes it hard to try again. Our team reads it differently: the crash is a sign that the effort outran what your system could recover from, and recovery capacity is something that can be trained.

How Long Does PEM Last?

It varies from person to person and from crash to crash. In a survey of 150 people with ME/CFS recruited partly from a clinic and online forums, the most common answer for how long PEM lasts was that it varies (45% of the 146 who answered). In that survey, only 9% said it reliably cleared within 24 hours, up to 84% said it could last a day or more, and 24% said their longest crashes lasted more than a week, sometimes months (Chu, 2018).

Recovery is slow even after a single test. Within 24 hours of a maximal exercise test, 85% of 23 sedentary women without chronic fatigue syndrome felt fully recovered, against none of 25 women with it, and only 1 of the 25 had recovered by 48 hours (VanNess, 2010).

Why Does a PEM Crash Often Hit a Day or More Later?

In our team's view, the bill comes during recovery: if you did more than your body could recover from overnight, the symptoms show up the next day or the one after, while it tries to catch up.

The timing isn't fixed: in that survey, 11% said PEM consistently started a day or more after the effort, up to 37% said it could, and 42% said the timing varied. Onset also varies the other way: 16% said PEM started immediately and 40% said it consistently started within 24 hours (Chu, 2018). In focus groups with 43 people, nearly half of participants reported everyday PEM symptoms beginning 12 to 48 hours after exertion (Stussman, 2020), and the IOM report cites studies finding worsening 1 to 7 days after exertion (IOM, 2015).

A second sign is how performance drops on a repeat test, which measures function. In 51 women with chronic fatigue syndrome and 10 sedentary women without it, who did 2 maximal exercise tests 24 hours apart, the 2 groups looked alike on day 1 and the women with chronic fatigue syndrome did significantly worse on day 2 (Snell, 2013). The authors noted that day 1 alone would appear to support a deconditioning hypothesis (Snell, 2013). In another group of 22 people with ME/CFS and no comparison group, peak oxygen use fell 13.8% from day 1 to day 2, and the work they could do at the ventilatory threshold fell 21.3% (Keller, 2014), while healthy adults typically repeat their peak within about 7% in other studies (Keller, 2014). That test can itself make symptoms worse, so it's no home experiment (IOM, 2015).

Ordinary muscle soreness lags too, peaking 1 to 3 days after exercise (Hotfiel, 2018; Vickers, 2001). Soreness is usually in the muscles you used, while a crash brings other symptoms such as trouble thinking, poor sleep and lightheadedness (VanNess, 2010), and it leaves you able to do less (IOM, 2015). Our team looks at whether you recovered well enough to repeat the effort. If you're in the middle of a crash, don't test yourself by repeating it.

Should You Rest or Push Through PEM?

Rest during a crash makes sense. In our team's view, strict rest for weeks at a time causes its own problems, because the body adapts to whatever you ask of it, and lying down most of the day can cost you ground at standing up. That view draws on healthy volunteers on head-down bed rest, a lab model of spaceflight that models severe inactivity more than an ordinary quiet stretch, and the studies cited here don't show that bed rest drives PEM. In small studies of those volunteers, blood volume was already down within 24 to 48 hours (Nakajima, 2008; Mauran, 2003). After 4 days of bed rest in 6 men, heart rate and sympathetic activity were up, parasympathetic activity was down, and their orthostatic tolerance had fallen to about half (Li, 2017). After 2 weeks in 12 volunteers, plasma volume was 17% lower and the heart's main pumping chamber had become smaller and stiffer (Levine, 1997). NICE advises against programmes built on the idea that deconditioning perpetuates ME/CFS (NICE, 2021), and our team's view is narrower: rest is right during a crash, and days or weeks of it can leave standing harder.

Pushing through has the opposite problem. If effort keeps leaving you worse for days, it's too big for now. Pull it back to a level you can recover from, repeat it, and then build. Getting stronger after a long stretch of illness is uncomfortable, and some of that discomfort feels like a flare, so our team judges each step by whether you recovered from it.

Pacing day to day has some support. In 81 people with ME/CFS followed for a year after a 114-person trial of other treatments, those who kept their spent energy at or below roughly 1.5 times the energy they felt they had improved in physical function and fatigue, while those who went beyond that didn't (Jason, 2009). The groups were sorted after the fact, so that shows a link, and the study can't show cause. PACE, a large trial of a therapy called adaptive pacing, found fatigue scores no different from specialist care alone (White, 2011). That therapy differs from energy-envelope pacing, and the pacing study above comes from the group that proposed the energy-envelope idea. Pacing is best treated as a self-management strategy whose benefit hasn't been proven.

NICE describes energy management as a self-management strategy that includes all types of activity (cognitive, physical, emotional and social), recognises that each person has a different and fluctuating energy limit, and is not curative. During a crash, NICE advises adjusting activity downward when symptoms are worse and raising it only after a period of stability, and it advises recognising a flare-up or relapse early and agreeing how to manage it (NICE, 2021).

If you're bedbound or housebound, this page isn't a plan for you to start alone. Pacing and rest come first, and any change should be overseen by your medical team (NICE, 2021).

Medication decisions belong to your prescriber, so check with them before you start, stop or change anything.

Can You Exercise With PEM?

Graded exercise therapy, a plan of fixed step-up increases in activity, was tested in a 2011 trial of people with chronic fatigue (a definition that didn't require PEM), where it modestly lowered fatigue scores (White, 2011). Those scores were rated by participants who knew which treatment they'd had (White, 2011). In 2021, the NICE guideline in England told clinicians not to offer graded exercise therapy or any programme with fixed increases to people with ME/CFS, and not to offer exercise as a cure. It allows a personalized programme only under a physiotherapist on a specialist team, starting below the level that worsens symptoms and adjusting up or down (NICE, 2021). NICE's decision rested on harms people with ME/CFS reported in qualitative research and on low-certainty evidence of benefit (NICE, 2021). PACE itself recorded serious adverse reactions in 2 of 160 people in the GET group and 2 of 160 on specialist care alone (White, 2011).

Our team agrees that fixed, step-up exercise plans fail many people with PEM, and our reason is specific. Building toward a target heart rate assumes the main problem is an out-of-shape heart. In our team's experience, deconditioning usually comes after the illness, from months of being unable to do much, and the thing that knocked you down in the first place is somewhere else. So our team finds the bottleneck first and spends your limited energy there and builds global fitness after that.

Say your balance system is off, so moving your head or watching things move around you makes you dizzy, and your brain struggles to hold its blood flow steady. A recumbent bike lets you do cardio lying back with your head still, and you may build some fitness on it. The moment you stand up and move around in real life, though, the same weak system breaks down again. The clinic would retrain the balance system first, so you can be up and moving without a big compensation, and then add general fitness on top.

Once that system holds, the clinic adds exercise while tracking the carbon dioxide you breathe out (end-tidal CO2). Low CO2 narrows the blood vessels in the brain and reduces its blood flow, known as hypocapnic cerebral hypoperfusion (Ainslie, 2009), so when that number starts to fall during exercise, our team takes it as the cue to take a break. In our team's experience, some people feel nothing yet when CO2 starts to fall, which is why a measurement helps more than waiting for symptoms.

What Limits You Upright in ME/CFS?

Tilt studies show lower blood flow to the brain upright in many people with ME/CFS, though they don't establish what causes it or that it causes PEM; the authors of one write that the exact cause "remains to be determined" (van Campen, 2020). In 429 adults with ME/CFS at 1 Dutch clinic, blood flow to the brain fell an average of 26% by the end of a head-up tilt, against 7% in 44 healthy people (van Campen, 2020). The CO2 they breathed out fell too, from 37 to 32 mmHg in the group whose heart rate and blood pressure looked normal (van Campen, 2020), though a later study in 535 women with ME/CFS found CO2 explained only a modest part of the drop in blood flow, and that their brain vessels respond to CO2 about like healthy women's do (van Campen, 2023). In 60 more adults at the same clinic, no difference was found in the drop in brain blood flow between those whose CO2 fell below 30 mmHg and those whose didn't (van Campen, 2021). Our team uses falling CO2 as a practical warning that breathing and blood flow control are slipping, and the studies above don't show that it predicts a crash. They also don't show that raising brain blood flow upright prevents PEM. Our team treats brain blood flow as one measurable piece of the picture.

Replay

In our team's experience, the flow drop has different causes in different people. These are 4 we see, and each is a hypothesis about why brain blood flow drops. The studies above don't show that any of them causes PEM:

• The balance system: For some people, going from lying down to standing is like stepping off a fair ride: the vestibular system is overwhelmed and can't do its part in steering blood flow.
• Pressure sensors in the neck: After a neck injury or an infection, the sensors that read blood pressure can have a hard time sensing how much it's changing with every heartbeat and breath, so the pressure readings fluctuate too much.
• The brain's own flow control: In some people, often after COVID, blood pressure can be normal all the way up to the neck, but the blood isn't getting transferred into the systems in the brain.
• Neck injuries: After a car accident, the sensors in the neck can make turning your head feel like that fair ride, which also disturbs how the brain controls its blood flow.

How Does Our Team Work on PEM Recovery?

This approach is the clinic's own, and none of the sources on this page is a clinical trial of it, so our team tracks it person by person with the same measurements it starts with.

There's no single protocol that fits everyone with ME/CFS, because the system that's breaking down differs from person to person. The order of work is the same:

1. Measure blood flow to the brain lying down and upright. A tilt table test with a transcranial Doppler and end-tidal CO2 shows whether it holds up. A tilt test can itself bring on a crash for some people, with symptoms lasting for several days afterward (IOM, 2015).
2. Find which system drops it. The clinic stresses each one, like turning your head or changing the pressure in your chest, and watches what happens to brain blood flow.
3. Spend your energy on that system. Use a dose you can recover from, like a band that helps you through your first pull-up.
4. Move from passive to active. Sitting up longer, then standing, then standing while turning your head and talking, then walking, and later jogging or rowing.
5. Measure again. Brain blood flow, CO2 and what you can do each day show whether the window is widening.

The order isn't a schedule, so the clinic holds a step, or goes back a step, whenever recovery slips, and nothing here is a fixed increase. NICE advises that any exercise programme for ME/CFS be overseen by a physiotherapist on a specialist team (NICE, 2021), so take this approach to your own medical team before changing your activity. In our team's experience, people who tolerate a small, well-chosen increase often report feeling better afterward, and we step back when they don't.

PEM Recovery: FAQ

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