Two people leave their appointments with the same instruction: walk a little more each week. One has had low back pain for a year. Her first longer walk leaves her sore that evening, the soreness is gone by morning, and a month later she is covering twice the distance. The other is six months past a viral illness. He feels fine during the walk and fine that night. Two days later he can barely get out of bed, and the slump lasts most of a week.
Same advice, opposite results. The first person had the ordinary soreness of doing more. The second may have post-exertional malaise (PEM), a delayed worsening of symptoms after effort that is a core feature of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and is common in long COVID.
Building activity gradually is the federal default for almost everyone with a chronic condition, and the evidence supports it, modestly. But advice to grade activity carries an unspoken qualifier, where appropriate, and that qualifier does most of the work. Exercise versus rest turns out to be the wrong question. The better one is whether effort makes you worse a day or two later.
The default: do what you can, and build slowly
The federal Physical Activity Guidelines for Americans, in a second edition that followed a 2018 scientific advisory committee report, set weekly targets for adults with chronic conditions or disabilities who are able to meet them: 150 to 300 minutes of moderate aerobic activity, plus muscle strengthening on at least two days. People who can’t reach those numbers, the guidelines say, should stay regularly active according to their abilities and avoid inactivity.
On safety, the guidelines’ message is about speed: activity should rise gradually over time, and inactive people should “start low and go slow,” beginning with lighter activity and adding frequency and duration bit by bit. Adults with chronic conditions or symptoms, the guidelines add, should be under a health care provider’s care, and can ask a clinician or a physical activity specialist which types and amounts suit their condition.
That advice reverses an old habit. The authors of a 2017 Cochrane overview noted that rest and inactivity were, for many years, among the standard recommendations for chronic pain.
A Centers for Disease Control and Prevention (CDC) page on physical activity for adults with disabilities, reviewed in April 2025, says nearly half of them get no leisure-time aerobic activity. Adults with disabilities were 82% more likely to be active when a doctor recommended it, yet only 44% of those who saw a doctor in the past year got that recommendation. The page’s references for those figures are CDC reports from 2014.
Two words in this field mean different things. Graded activity is a planned, stepwise increase toward a target, with the steps set in advance. Adapted activity changes the form instead: a seated position, shorter bouts, a hand cycle instead of a walk, equipment or a helper. CDC notes that most aerobic activity may need to be modified or adapted for people with disabilities. Fitting particular sports and exercises to particular disabilities is the territory of our article on adapted movement.
What graded activity means in chronic pain
In pain treatment, graded activity has a specific lineage. A 2011 review from Utrecht University described the classic program: tests of functional capacity, a visit to the person’s workplace, back-school education, and an individual exercise program kept below maximum effort and increased step by step. Its engine is operant conditioning, a behavioral method: you work to a preset quota instead of stopping when pain flares. The plan, not the symptom of the day, sets the dose.
A cousin method, graded exposure, targets fear. Instead of building general fitness, it walks a person step by step through the specific movements they have come to dread, such as bending to lift a laundry basket.
What the back pain trials found
The benefits are real and small. A 2010 review in the journal Physical Therapy, led by researchers at the University of Sydney, examined 15 trials with 1,654 people with persistent low back pain. Against minimal treatment or none, graded activity lowered pain by about 6 points on a 100-point scale in the short term, with similarly small gains in disability. Against other forms of exercise, in six trials, it made no significant difference. Graded exposure did about as well as graded activity.
A 2016 meta-analysis in Pain Medicine landed in the same place. Graded activity cut disability more than control conditions did, in both the short and long term, but beat other exercise on no measure at all. Graded exposure outperformed it in the short term on disability and on catastrophizing, a habit of expecting the worst about pain. The Utrecht review, which used a different method of weighing five trials with 680 patients, found no or insufficient evidence of benefit for pain, disability or return to work.
So the belief that graded activity is a special, superior back pain program doesn’t survive the trials. On the library’s evidence scale, it earns positive evidence of a small benefit over doing little, with no edge over other exercise. One reasonable reading is that getting moving matters more than which structured method gets you there. How exercise therapy compares with surgery and injections is weighed in our physical therapy guide, and what back pain guidelines recommend is laid out in our back pain explainer.
Across chronic pain, the evidence is thin
The broadest look is that 2017 Cochrane overview, led from the University of Dundee in Scotland. It gathered 21 Cochrane reviews covering 381 studies and 37,143 participants, with conditions from arthritis and fibromyalgia to neck disorders, painful periods and post-polio syndrome. Not one review studied chronic pain as a general condition, and none involved ME/CFS. Physical function improved in 14 reviews, mostly by small to moderate amounts, while pain results were inconsistent. The authors’ bottom line was blunt: “The quality of the evidence examining physical activity and exercise for chronic pain is low.”
Only a quarter of the studies actively reported side effects. Where they did, the usual problem was extra soreness or muscle pain that faded after a few weeks.
Fibromyalgia shows the same pattern of real but modest gains, which our fibromyalgia article sets out. On harms, a 2017 Cochrane review of aerobic exercise for fibromyalgia found that most trials never measured adverse events. Slightly more people dropped out of exercise groups than control groups, about 20 per 100 against 17, a gap small enough to be chance.
Where the default breaks: post-exertional malaise
PEM is not ordinary soreness. CDC describes it as a flare of symptoms after physical, mental or emotional effort that the person could have handled easily before getting sick. The worsening usually shows up 12 to 48 hours later and may persist for days or weeks. For some people, CDC adds, bright light or noise alone can be enough.
The soreness reported in chronic pain exercise studies usually faded within weeks of starting. PEM can follow a demanding conversation as readily as a walk, can bring thinking problems as well as aching muscles, and, CDC says, can put a patient into a relapse lasting days, weeks or longer.
For people with ME/CFS, CDC’s clinician guidance warns that standard exercise advice for healthy people can do substantial harm, and that these patients cannot tolerate such routines. CDC does not tell them to stop moving, though. Deconditioning is harmful too, it says, so people should keep up the activities they can tolerate. Those who tolerate their current level may benefit from carefully increasing exercise, and better tolerance of aerobic exercise is a long-term goal, to be pursued cautiously.
That is a genuine trade-off. CDC’s provider toolkit on PEM notes that inactivity can lead to muscle deconditioning, and also that more activity can be harmful if it brings on PEM.
What happens in muscle after a crash
A 2024 study from Amsterdam, published in Nature Communications, looked inside the muscle. Researchers recruited people with long COVID whose illness included PEM and compared them with people who had recovered fully from COVID-19. Everyone did a maximal cycling test, with thigh-muscle biopsies before the test and the day after. Every patient developed PEM, with muscle pain, worse fatigue and thinking problems lasting up to a week.
After the test, patients’ muscles showed more signs of tissue damage than the recovered volunteers’ did, along with metabolic disturbances. Patients also started out with more amyloid-containing deposits, clumps of protein in the muscle, though these rose about equally in the two groups after the test. The study enrolled only people with severe long COVID. They were not bedbound, averaging roughly 4,000 steps a day, and the authors argued that inactivity could not explain the abnormalities. They also said the study was observational and small, could not establish cause, and needs repeating in other groups.
That finding concerns people with PEM after a deliberately exhausting test. It does not show that exercise damages muscle in everyone with long COVID.
The American Academy of Physical Medicine and Rehabilitation (AAPM&R) drew the clinical lesson in a 2025 consensus statement from its long COVID collaborative, which includes clinicians from more than 40 centers along with patients and government representatives. Activity advice has to match each patient’s current tolerance, it says, because overly intense activity can trigger PEM and worsen muscle damage. It warns that when PEM is present, well-meant advice to exercise through fatigue can make things worse, and it calls for energy-conservation strategies and a slow, carefully adjusted return to activity at less than maximal effort.
The ME/CFS reversal, briefly
ME/CFS is where this argument played out first. In 2011 the British PACE trial reported modest self-rated gains from graded exercise therapy in patients who met the Oxford criteria, an older case definition. England’s National Institute for Health and Care Excellence (NICE) reversed course in its 2021 guideline: graded exercise therapy, and any program that raises activity in fixed increments, should not be offered. That account comes from a 2022 primary care briefing by authors from a London research group and the Myalgic Encephalomyelitis Association. Cochrane’s review of exercise for the condition, whose searches stopped in 2014, now carries an editorial note that a pilot project toward updating it has been discontinued. More than 50 clinicians and researchers, led by PACE investigator Peter White, called the NICE change controversial, arguing among other things that the trials had delivered graded exercise flexibly, with each step negotiated with the patient and tailored to symptoms. A less-cited 2010 trial of 296 patients in northwest England found that a nurse-led home program of gradually increasing activity eased fatigue slightly at 20 weeks, with no significant difference in fatigue or physical function a year after treatment ended. Our ME/CFS article tells the full story of that dispute.
Long COVID: two paths, sorted by PEM
Long COVID is where the where appropriate question is being tested most directly. A 2025 review in Archives of Physical Medicine and Rehabilitation, led from Western University in Canada, gathered the small rehabilitation literature. Five studies, with 193 patients, found fewer and milder PEM episodes after rehabilitation built around pacing. Eight studies, with 1,080 patients, tracked PEM as a side effect of individually tailored rehabilitation that included exercise, and seven found no sign that the exercise set off crashes.
Every one of those studies carried a high or very high risk of bias. The authors’ cautious reading: some people with long COVID don’t have PEM, and limited evidence suggests supervised, individually tailored rehabilitation adjusted to symptoms may not trigger it in that group. By the library’s evidence scale, this counts as insufficient so far, though it fits the logic of sorting people first.
A trial funded by the National Institutes of Health built in that sorting. RECOVER-ENERGIZE screened adults with long COVID and exercise intolerance for PEM, then sent them down one of two paths: personalized cardiopulmonary rehabilitation for people without significant PEM, or structured pacing for those with it. Screening for the rehabilitation path even checked for a symptom flare 48 to 72 hours after a walking test. The trial registry lists the rehabilitation arm, with 360 participants, as completed in May 2026 with no results posted. The design paper, posted in June 2026, is a preprint that has not been peer reviewed. The pacing arm is described in our explainer on what pacing means.
AAPM&R adds a point that applies with or without crashes. When someone describes their fatigue as low tolerance for activity, other treatable causes deserve a look, including heart, lung, hormonal, nutritional, metabolic and chronic infectious disorders. The wider picture of long COVID sits in our article on symptoms that linger after infection, and the contrast between easing back after a cold and after long COVID is the focus of our return-to-activity piece.
Is your activity plan working? Signs to watch
A graded or adapted plan is a test. This guide is our own, drawn from the sources above; it is not a diagnosis, and the last column is a conversation starter for whoever set the plan.
| What you notice | What it often reflects | What to raise |
|---|---|---|
| Soreness or stiffness the same day or next, easing within a day or two and fading over weeks | The usual response to doing more | Nothing, unless it stops fading |
| You can repeat last session and daily tasks feel a little easier | Progress | When the next step should come |
| A worse day 12 to 48 hours after effort, lasting days | The timing CDC describes for PEM | Whether PEM has been assessed before the plan goes on |
| A crash after a stressful meeting, a hard conversation or a noisy room, not just exercise | Also consistent with PEM | The same question |
| Sessions only happen if work, chores or family time get dropped | The plan may cost more than it adds | Whether the targets or type of activity fit |
| No change in function by the agreed review date | The plan may not suit you | What else should be checked, and what comes next |
Three things are worth settling before a plan starts:
- How the steps are set. A fixed schedule, your response to the last step, or both.
- What counts as a setback. Agree in advance which symptoms, how long after effort and lasting how long, would send the plan back for review.
- When it gets reviewed. A set date, not an open-ended wait. (A simple running note of what you did and how you felt one and two days later, like the log in our article on how long fatigue lasts, makes the delayed pattern visible.)
When to get help
- Before a new program, if you live with a chronic condition or ongoing symptoms. The federal guidelines advise being under a provider’s care; which types and amounts of activity fit is a question for that clinician or a physical activity specialist.
- When ordinary activity is followed a day or two later by a slump that lasts days. Whether that is PEM is a diagnostic question for a clinician, not something to test by pushing harder, because the answer changes the plan.
- When low activity tolerance is the main problem, crash or no crash. AAPM&R’s list of other causes to rule out, from heart and lung problems to hormonal and nutritional ones, is worth working through with a clinician.
- Emergencies. The National Heart, Lung, and Blood Institute lists chest pain, heaviness or discomfort; pain or discomfort in an arm, the back, shoulders, neck or jaw; shortness of breath at rest or with a little activity; heavy sweating; lightheadedness or sudden dizziness; and a rapid or irregular heartbeat among heart attack warning signs. If any of these come on during or after activity, call 911; NHLBI’s advice is to call even without certainty that it’s a heart attack.
The question that sorts the advice
Doing what you can and building slowly fits most people with chronic pain or chronic illness. The evidence says it helps modestly, and about as much as other kinds of exercise. For people whose symptoms flare a day or two after effort, CDC and rehabilitation specialists say the same advice can harm, and that activity should instead be matched to tolerance.
The single most useful habit is to notice how you feel 24 to 48 hours after effort, not just during it. Bring that answer to whoever writes your plan, and agree in advance on what the plan does when the answer changes.
Sources
- US Department of Health and Human Services, Office of Disease Prevention and Health Promotion. “Physical Activity Guidelines for Americans, 2nd edition: Executive Summary.” odphp.health.gov
- Centers for Disease Control and Prevention. “Increasing Physical Activity among Adults with Disabilities (last reviewed April 7, 2025).” cdc.gov
- Centers for Disease Control and Prevention. “IOM 2015 Diagnostic Criteria (ME/CFS, for health care providers; last reviewed May 10, 2024).” cdc.gov
- Centers for Disease Control and Prevention. “Strategies to Prevent Worsening of Symptoms (ME/CFS, for health care providers; last reviewed May 10, 2024).” cdc.gov
- Centers for Disease Control and Prevention. “Managing Post-Exertional Malaise (PEM) in ME/CFS (provider toolkit, CS321382-D).” cdc.gov
- National Heart, Lung, and Blood Institute. “Heart Attack: Symptoms (last updated March 24, 2022).” nhlbi.nih.gov
- ClinicalTrials.gov (National Library of Medicine). “RECOVER-ENERGIZE Platform Protocol, Appendix A (Exercise Intolerance), NCT06404060 (status: completed).” clinicaltrials.gov
- medRxiv (preprint, not peer reviewed). “Friedly J, Bateman L, Berdan LG, et al. "Rationale and Design of RECOVER-ENERGIZE: A Platform Clinical Trial of Interventions for Exercise Intolerance With and Without Post-exertional Malaise in Long COVID." June 3, 2026. PubMed. DOI: 10.64898/2026.06.02.26354455.” doi.org
- PM&R (American Academy of Physical Medicine and Rehabilitation). “Cheng AL, Herman E, Abramoff B, et al. "Multidisciplinary collaborative guidance on the assessment and treatment of patients with Long COVID: A compendium statement." PM R, 2025;17(6):684-708. PubMed. DOI: 10.1002/pmrj.13397.” pubmed.ncbi.nlm.nih.gov
- Cochrane Database of Systematic Reviews. “Geneen LJ, Moore RA, Clarke C, Martin D, Colvin LA, Smith BH. "Physical activity and exercise for chronic pain in adults: an overview of Cochrane Reviews." Cochrane Database Syst Rev, 2017;4:CD011279. PubMed. DOI: 10.1002/14651858.CD011279.pub3.” pubmed.ncbi.nlm.nih.gov
- Physical Therapy. “Macedo LG, Smeets RJ, Maher CG, Latimer J, McAuley JH. "Graded activity and graded exposure for persistent nonspecific low back pain: a systematic review." Phys Ther, 2010;90(6):860-79. PubMed. DOI: 10.2522/ptj.20090303.” pubmed.ncbi.nlm.nih.gov
- Pain Medicine. “López-de-Uralde-Villanueva I, Muñoz-García D, Gil-Martínez A, et al. "A Systematic Review and Meta-Analysis on the Effectiveness of Graded Activity and Graded Exposure for Chronic Nonspecific Low Back Pain." Pain Med, 2016;17(1):172-88. PubMed. DOI: 10.1111/pme.12882.” pubmed.ncbi.nlm.nih.gov
- Disability and Rehabilitation. “van der Giessen RN, Speksnijder CM, Helders PJM. "The effectiveness of graded activity in patients with non-specific low-back pain: a systematic review." Disabil Rehabil, 34(13):1070-6 (published online December 2011). PubMed. DOI: 10.3109/09638288.2011.631682.” pubmed.ncbi.nlm.nih.gov
- Cochrane Database of Systematic Reviews. “Bidonde J, Busch AJ, Schachter CL, et al. "Aerobic exercise training for adults with fibromyalgia." Cochrane Database Syst Rev, 2017;6:CD012700. PubMed. DOI: 10.1002/14651858.CD012700.” pubmed.ncbi.nlm.nih.gov
- Nature Communications. “Appelman B, Charlton BT, Goulding RP, et al. "Muscle abnormalities worsen after post-exertional malaise in long COVID." Nat Commun, 2024;15(1):17. PubMed. DOI: 10.1038/s41467-023-44432-3.” pubmed.ncbi.nlm.nih.gov
- Archives of Physical Medicine and Rehabilitation. “Pouliopoulou DV, Hawthorne M, MacDermid JC, et al. "Prevalence and Impact of Postexertional Malaise on Recovery in Adults With Post-COVID-19 Condition: A Systematic Review With Meta-analysis." Arch Phys Med Rehabil, 2025;106(8):1267-1278. PubMed. DOI: 10.1016/j.apmr.2025.01.471.” pubmed.ncbi.nlm.nih.gov
- The Lancet. “White PD, Goldsmith KA, Johnson AL, et al. "Comparison of adaptive pacing therapy, cognitive behaviour therapy, graded exercise therapy, and specialist medical care for chronic fatigue syndrome (PACE): a randomised trial." Lancet, 2011;377(9768):823-36. PubMed. DOI: 10.1016/S0140-6736(11)60096-2.” pubmed.ncbi.nlm.nih.gov
- Healthcare (Basel). “Kingdon C, Lowe A, Shepherd C, Nacul L. "What Primary Care Practitioners Need to Know about the New NICE Guideline for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome in Adults." Healthcare (Basel), 2022;10(12):2438. PubMed. DOI: 10.3390/healthcare10122438.” pubmed.ncbi.nlm.nih.gov
- Cochrane Database of Systematic Reviews. “Larun L, Brurberg KG, Odgaard-Jensen J, Price JR. "Exercise therapy for chronic fatigue syndrome" (republished with editorial note dated December 19, 2024, amended January 31 and March 25, 2025). Cochrane Database Syst Rev, 2024;12:CD003200. PubMed. DOI: 10.1002/14651858.CD003200.pub9.” pubmed.ncbi.nlm.nih.gov
- Journal of Neurology, Neurosurgery and Psychiatry. “White P, Abbey S, Angus B, et al. "Anomalies in the review process and interpretation of the evidence in the NICE guideline for chronic fatigue syndrome and myalgic encephalomyelitis." J Neurol Neurosurg Psychiatry, 2023;94(12):1056-1063. PubMed. DOI: 10.1136/jnnp-2022-330463.” pubmed.ncbi.nlm.nih.gov
- BMJ. “Wearden AJ, Dowrick C, Chew-Graham C, et al. "Nurse led, home based self help treatment for patients in primary care with chronic fatigue syndrome: randomised controlled trial." BMJ, 2010;340:c1777. PubMed. DOI: 10.1136/bmj.c1777.” pubmed.ncbi.nlm.nih.gov