Tag: exercise

Explaining Fatigue and Post-Exertional Malaise in Long COVID and ME/CFS: From Skeletal Muscle To Exercise Immunology

Abstract:

The SARS-CoV-2 viral outbreak in 2020 resulted in a record number of global hospitalizations and deaths. Although most people recover from an initial COVID infection within 3 months, around 10% of people have symptoms that do not improve after 3 months, which is called long COVID. Other viruses and bacterial infections can also result in long-term symptoms, which is known as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).

One of the most common symptoms of long COVID or ME/CFS is post-exertional malaise, which is the worsening of symptoms or development of new symptoms after physical, mental or emotional stress. This can lead to patients leading less physically active lifestyles. Physical activity is known to be beneficial for overall health and wellbeing, mostly by increasing exercise capacity, which is a significant predictor in long-term health. Physical inactivity.

It is thought that many symptoms of long COVID and ME/CFS can be explained by lower physical activity of patients. However, people who are less physically active don’t experience post-exertional malaise, implying there are disease-specific changes. Many of the benefits that come from exercise come from a persons ability to adapt to an exercise session. Usually, exercise will create a short energy deficit, which then may result in small amounts of muscle damage. This then triggers a short-lived immune response, led first by neutrophils and macrophages, which result in activation of fibroadipogenic progenitor cells (FAP cells) and satellite cells (muscle stem cells). FAP cells and satellite cells communicate to repair damage to the muscle itself, while immune cells clear debris surrounding the muscle. In healthy situations, this creates a stronger, more resilient muscle. It is unknown whether these responses are still seen in long COVID or ME/CFS. The goal of this thesis then to 1) understand muscle changes in patients with long COVID and ME/CFS, 2) to better understand how these changes may relate to PEM, 3) to understand whether the muscle changes in patients are a result of physical inactivity.

Within the thesis, I find that patients with long COVID and ME/CFS have specific patterns of skeletal muscle that separate them from healthy individuals. This is highlighted by more fast-twitch fibre types, slow-twitch muscle atrophy, lower mitochondrial respiration that is separate from just mitochondrial loss, less metabolites related to oxidative capacity and antioxidation, less lipids that are required for cell membrane maintenance, and lower amounts of satellite cells and FAP cells.

Beyond this, I find that ME/CFS can be distinguished from long COVID by less capillaries, less slow-twitch fibres, less local immune cells, and lower amounts of several essential amino acids. As well, I find evidence that physical inactivity alone cannot explain long COVID and ME/CFS symptoms. Where all of long COVID, ME/CFS, and physical inactivity have lower whole-body aerobic capacity, physical inactivity causes a decrease in muscle fibre size, loss of mitochondria, increases in muscle lipotoxic lipids, and decreases in metabolites related to carnitine metabolism. These changes are not seen in either long COVID nor ME/CFS, and support the idea that long COVID and ME/CFS have disease specific muscle changes.

Overall, I find that the reduced whole-body capacity of long COVID and ME/CFS patients is not cause by physical inactivity, and is defined by reduced muscle oxidative ability. The lower amounts of local cells that would normally support exercise and damage responses are lower in both long COVID and ME/CFS, which partially explains the occurrence of PEM. This also suggests that patients experiencing PEM should not undertake normal rehabilitation, however it might be that more individually tailored, and severely monitored approaches may still be beneficial.
Source: Charlton, B. T. (2026). Explaining Fatigue and Post-Exertional Malaise in Long COVID and ME/CFS: From Skeletal Muscle To Exercise Immunology. [PhD-Thesis – Research and graduation internal, Vrije Universiteit Amsterdam]. https://doi.org/10.5463/thesis.1979 https://research.vu.nl/en/publications/explaining-fatigue-and-post-exertional-malaise-in-long-covid-and-/ https://research.vu.nl/ws/portalfiles/portal/517511531/aio01877%20braeden%20charltonfinal%20-%206acf4153820e1.pdf (Full text)

“The Prisoner”

Case Histories of ME/CFS: “The Prisoner”
ProHealth.com
by David S Bell, MD, FAAP
April 4, 2012

This is the case history of a man whose fear of relapse 4 years after sudden onset of ME/CFS nearly robbed him of recovery. It is excerpted from Dr. Bells free e-book Faces of CFS – Case Histories of Chronic Fatigue Syndrome, published in August, 2000 ( David S Bell, MD, 2000).

Reprinted with the kind permission of ProHealth: 4/4/12

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THE PRISONER

It is so ironic that while most doctors see CFS as hypochondriasis, I feel that hypochondriasis may be the result of the combination of CFS and the physician ignorance. Patients must sail these waters without guidance, forcing them to make it on their own.

Those of us in good health rarely appreciate our good fortune. We live our lives ravenously, devouring the minutes of the day with work, play, love – ever eager for the next course. We charge ahead, assuming life will go on as always.

In order to accomplish this, we allow ourselves to be oblivious to the suffering of others. We push their pain to the deep recesses of our subconscious, and remain blind to the fact that around the corner may lie an event that will change the foundation of our lives with similar finality.

Gary Burns was just like the rest of us. There was nothing malevolent about his view of life; he harbored no evil intentions. Yet, he was as unaware of the suffering of others as the rest of the world was about to be of his own suffering.

Like most patients, Gary’s ordeal began with a bout of what he assumed must be flu. He was 37, robust and active, a husband and a father.

This flu announced itself to Gary one day in October of 1986. The course of Gary’s illness, and the eventual dissolution of everything that he had once taken for granted, was typical for an adult who experiences what we doctors call sudden onset of chronic fatigue syndrome (ME/CFS).

Initially, he was offered a months sick leave by his company, a nearby factory. He tried to go back to work when his sick leave ended, but often he felt in a state of collapse by noon, and had to leave the jobsite.

He took an extended leave of absence, hoping for recovery. If he could just catch up on his sleep, he kept telling himself and others, all would be well. Gary had moments during the day when he found the strength to shower, wander through his house, and ponder the possibility of returning to his job. But, soon enough, it would return, and he would tumble onto the sofa and sleep the day away.

Gary still had no idea what it was, and his doctor hadnt a clue, either. Gary had been ill for six months when his doctor announced that he had been unable to discover a medical explanation for Gary’s symptoms.

He advised Gary to snap out of it, to get more exercise, and to see a psychiatrist.

Like a lot of people, Gary trusted his doctor and believed what his doctor had told him. With some embarrassment, and worry over the expense, Gary arranged an appointment with a psychiatrist. After all, he was desperate, and willing to try anything. The psychiatrist probed for information about Gary’s life, and Gary answered the psychiatrists questions honestly.

He said he was in the process of being fired, and that he was going broke.

He confessed he had been unusually irritable, chastising his kids for creating noise and havoc in the house, and sulking whenever his wife tried to comfort him.

In a revelation that was somewhat difficult for him, Gary admitted he was depressed.

The doctor prescribed an antidepressant, and invited Gary to continue therapy in order to resolve emotional conflicts – conflicts that the psychiatrist suggested were the cause of Gary’s disabling illness.

The following day, however, when Gary took the first pill, he rapidly deteriorated, feeling as if he had been hit full force by a freight train.

He slept for two days, and when he was finally able to stay awake, he felt hung over, as if he had drunk a case of liquor the night before. Perhaps not surprisingly, Gary decided to cancel his next appointment.

The psychiatrists secretary insisted the antidepressant could not possibly have caused Gary’s severe reaction. She also advised him he would be charged for the appointment, whether he showed up or not. So much for psychiatry, Gary thought, and never returned. By then, Gary felt as if he was riding a wild and powerful horse, but the reins had slipped from his hands.

Desperation was a daily staple, and as he lay in a helpless mound on his bed, or the sofa, he searched his mind frantically for solutions.

His mother, whom he had frequently accused of being a health nut, owned a health food store. Gary decided to sample the assorted vitamins and nostrums available in his mothers shop. He began eating organic food and taking vitamins for the first time in his life, although he noticed no immediate improvement.

On his worst days, he wondered if he had a terminal illness, especially cancer, that his doctor had missed. He decided to read everything he could about cancer; if the doctors were incapable of discovering the cause of his symptoms, he would become a doctor himself.

In the course of his reading journey, Gary came upon an article that described CFS.

The stories of the patients in this article resonated with his own experience of the disease: sudden onset; a long, chronic course, exhaustion, headaches, pain; sensitivity to light, night sweats, the sensation – if not the reality – of high fever.

He was stunned when he read that patients with CFS are exquisitely sensitive to many drugs, including anti-depressants such as the one he had taken. He felt as if he was reading his own biography. In fact, he was so persuaded that the long-standing mystery of the last year was resolved, he felt incredulous that his doctor had missed the obvious signs, which now seemed so obvious.

There was just one small detail of the disease, as CFS was described in the article, that didnt seem to fit: Gary had never really thought of himself as a Yuppie [with Yuppie Flu].

Certain of his diagnosis, nonetheless, Gary plunged headlong into health nut-ism, with his mothers encouragement and guidance. He eliminated fat from his diet and took handfuls of vitamins. He waded through lengthy discussions of echinacea, germanium, and zinc. Still, he remained unable to work.

Even though previous attempts to exercise had ended in disaster, Gary next decided workouts might be the solution to his nightmare.

He committed himself to pushing past the sore throats and exacerbated fatigue that had followed on the heels of vigorous activity on other occasions. In fact, he gave it everything he had, beginning with a brisk, one-mile walk each day.

On day four, however, when he tried to jog, he felt so suddenly weak at a juncture in the road not far from his house, he wondered whether he would be able to make his way back on two feet. He was completely bedridden for the next two weeks.

Gary felt hopeless.

He had been fired, and most of his friends had dropped him, seeming to have forgotten about everything they had once shared in common.

The medical profession seemed utterly ignorant of his condition.br />

A day rarely passed when he failed to ponder suicide, but the notion of leaving such a traumatic legacy for his children always pulled him up short.

Now, he became exceedingly cautious with his body.

He cloistered himself from the noise and activity of his family.

He woke at nine, downed his vitamins, and showered, and then he rested.

At noon, he ate a health nut lunch of fruits and grains, and then he rested.

In the late afternoons, he attempted a few chores and stretched his muscles in the quiet of his living room. His children stayed with neighbors after school until his wife returned from work.

Together, the family ate a nutritious dinner. Afterward, Gary rested.

At ten, he went to bed, where he lay quietly until he fell asleep at midnight.

Two years of Gary’s life passed in this way.

Most of what was important to him before the onset of CFS had dissolved in those two years. His children became used to their new father, the one who could not play baseball or take them to the county fair. They began to forget their old father.

And then something wonderful happened: Gary started to get better.

The severity of his daily headache lessened, as did the crushing fatigue; he was able to be more active. Gary felt confident that his improvement was due to his adherence to his rigid schedule of the previous two years.

In the third year of his illness he told me he felt he was functioning at about 70% of his pre-CFS activity level.

Still, he planned his days with great care, taking a short walk just twice a week, playing catch with his children each day. He told me proudly that he could ride the lawn mower and cut the entire lawn without stopping to rest in the middle of the job.

It was apparent that he had finally accepted his new life; his despair was gone.

By the fourth year Gary complained only of persistent fatigue, muscle aching, and the fractured, disturbed sleep patterns that are common to virtually all CFS patients, and, in fact, are one of the most pervasive hallmarks of the disease.

Although Gary’s symptoms were less severe than they had been in the past however, he continued his rigid adherence to a reduced level of activity. He believed that his careful attention to what he ate and his meager exercise regime was responsible for his improvement; that he had finally regained control of his destiny.

I became worried – not about the illness, but about Gary’s nearly obsessive concern with over-exerting himself. He had become his own prisoner, caught up in self-imposed rules and regulations that severely limited his experience of the world. One day, I voiced my concerns. I told him that he was both his own jailer and inmate.

I told him he needed to take some risks. I suggested exercise.

His mouth nearly fell open, recalling his own disaster with exercise two years before. Most CFS patients have learned through bitter experience that efforts to surmount their disability and engage in the kind of exercise activities they routinely performed before they fell ill is unlikely to have a good result.

But the problem is not exercise, it is the assumption that exercise will by definition change the course of the illness.

For patients with severe illness, exercise does not change the course and may lead to worsened symptoms.

But if CFS is getting better, exercise is great and may speed the recovery.

I suspected Gary was no longer in the severe illness category. In fact, I was uncertain whether his reduced activity level, which continued to hover around 70% of what was normal for him, was due to CFS, or due to physical de-conditioning as a result of his fear of exertion.

After all, he had been monitoring himself like an organism under a microscope for three years. Granted, he had learned the brutal limits of his disease through suffering, but it seemed to me that he was becoming almost hypochondriacal in his attention to his body.

It is so ironic that while most doctors see CFS as hypochondriasis, I feel that hypochondriasis may be the result of the combination of CFS and the physician ignorance. Patients must sail these waters without guidance, forcing them to make it on their own.

Of course, the only way to find out was to ask Gary to exercise, and he and I both knew the proposition was risky.

Which is better: to exist safely in a compulsively rigid way of life? Or try for a full-out, 100% return to normalcy – at the risk of initiating a relapse that might turn the clock back for Gary by months or even years?

Gary reminded me that it was his life I was risking by making such a request, not my own. Good point. I was asking him to throw away his fear of the pain and suffering of the past years, all the while courting its return. Did I have that right? I had come to know Gary well by then. My observations and intuition led me to believe that Gary was going to be one of the lucky ones; he was going to beat the illness.

All signs pointed to continued improvement.

If my suspicions were in error, I thought, Gary would have a relapse, but he would likely recover from it within a month.

And, more importantly, at least we would have our answer. He would still be a prisoner, but he would be prisoner of the disease, not his own fear.

After a great deal of discussion, Gary finally agreed to try.

We planned an exercise program that was extremely gentle.

Most healthy people wouldnt have considered it an exercise program at all.

We planned stretching exercises, then slow walking, then brisk walking – depending upon the progress, if any.

When Gary joked that he was dedicating his body to science, his wife frowned. In the beginning, Gary experienced significant anxiety, and increased muscle aching, as well. But, over a period of weeks, the quality of his sleep began to improve, along with a decrease in the muscle pain.

In fact, at the end of two months, it was clear to Gary and to me that he was better.

And when his fear began to diminish, he became more willing to venture out into the world of the living. After three months, he had even more energy, and felt confident and enthusiastic about life to a degree he had not experienced for years.

This is not to say his fatigue evaporated. He was tired, sometimes very tired. But, as Gary pointed out, it was good tiredness, not a CFS tiredness.

In the complicated realm of CFS, where there remain so many unanswered questions, I am not sure what recovery actually means.

I often wonder whether the illness vanishes completely, leaving the patient the same as before,

Or if it simply recedes in the background, becoming mild enough that the patient learns to ignore its nagging distractions.

Both probably occur.

In a study Mary Robinson did of our patients, 20% remained disabled after 15 years. Of the remaining 80%, half persisted with symptoms although they were able to lead relatively normal lives.

Several years have passed for Gary and we continue to stay in touch. He has clearly entered that privileged circle of CFS patients who actually recover fully from the disease. I do not think that his continued recovery can be attributed to exercise, or even the vitamins, but who knows?

I do feel that if Gary had not tried the exercise, he would have stayed in his prison for the rest of his life. Gary recovered for reasons that are mysterious, but he needed to take a leap of faith in order to demonstrate the recovery to himself.

Gary doesnt really think about these issues very much anymore. He is working again, and engaged once more in the lives of his spouse and children. Nevertheless, he has been changed profoundly by his experience. He left his prison of four years, but as a different man. He carries with him an appreciation of his incredible good luck. His suffering now is confined to feeling the suffering of others who are in pain.

When he watches the news on television, and there is a story about AIDS or multiple sclerosis or cancer or CFS, he does not rush to change the channel as he once might have done.

Instead, his eyes fill with tears.

– David S Bell, MD, Aug 15, 2000

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Note: This information represents the experience and opinions of Dr. David Bell. It is generic and for general information purposes only. ME/CFS/FM is an extremely complex illness, and such general information may not be appropriate for an individual with this illness. Therefore, should you be interested in the ideas presented here, please discuss them with your personal physician.

Hemodynamic Phenotyping in ME/CFS and ANOCA: Complementary Insights from Coronary Function Testing and Invasive Cardiopulmonary Exercise Testing

Abstract:

This single-center cohort study sought to evaluate the association between Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and Angina with Non-Obstructive Coronary Arteries (ANOCA), by determining the observed frequency of ME/CFS among patients with ANOCA diagnosed by coronary function testing (CFT). Additionally, we performed an exploratory analysis of the diagnostic utility of invasive cardiopulmonary exercise testing (iCPET) in ME/CFS patients with CFT-confirmed ANOCA, with the aim of identifying the predominant physiological mechanism responsible for exertional limitation in this population.

Systematic medical record review of 261 patients with CFT-confirmed ANOCA was performed using standardized diagnostic criteria to identify concurrent ME/CFS diagnosis. ME/CFS was identified in 47 patients, representing an observed frequency of 18%. The only statistically significant difference between ANOCA patients with and without ME/CFS was a higher frequency of connective tissue disease in the ME/CFS group (p = 0.0221). In a separate cohort of 27 patients with ME/CFS who underwent iCPET, 24 patients (89%) had CFT-confirmed ANOCA.

The diagnosis of ANOCA by CFT prompted a change in medical management in 81% of patients in this cohort. iCPET revealed a primary peripheral limitation to exercise, characterized by impaired peak systemic oxygen extraction despite normal peak oxygen delivery. This study demonstrates a clinically significant association between ME/CFS and ANOCA.

These findings underscore the clinical value of CFT in patients with ME/CFS and exertional chest pain and highlight iCPET as a complementary tool for hemodynamic phenotyping in this population. Prospective studies incorporating simultaneous CFT and iCPET with molecular phenotyping are warranted.

Source: Mackay Z, Shah S, Villalobos JG, Latif N, Arun A, Joseph P, Heerdt P, Singh I. Hemodynamic Phenotyping in ME/CFS and ANOCA: Complementary Insights from Coronary Function Testing and Invasive Cardiopulmonary Exercise Testing. Am J Physiol Heart Circ Physiol. 2026 Sep 21. doi: 10.1152/ajpheart.90080.2026. Epub ahead of print. PMID: 42767811. https://journals.physiology.org/doi/abs/10.1152/ajpheart.90080.2026 (Full text available as PDF file)

Skeletal muscle properties in long COVID and ME/CFS differ from those induced by bed rest

Abstract:

Patients with long COVID and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) suffer from post-exertional malaise. The accompanying physical inactivity may contribute to a lower aerobic capacity and may explain skeletal muscle adaptations in these patients. Here, we compare whole-body exercise responses and skeletal muscle adaptations after strict 60-day bed rest in healthy people with those in long COVID and ME/CFS patients, and healthy age- and sex-matched controls.

Bed rest alters respiratory and cardiovascular responses to maximal exercise, which are dissimilar in patients. Bed rest causes muscle atrophy without altering fiber type. Both patient groups have more glycolytic fibers, and ME/CFS patients display type I-specific atrophy. Only after bed rest is oxidative phosphorylation capacity associated with maximal oxygen uptake.

As skeletal muscle characteristics differ between patients and healthy individuals after bed rest, physical inactivity cannot solely explain the lower exercise capacity and skeletal muscle adaptations in long COVID and ME/CFS patients.

Source: Charlton BT, Slaghekke A, Appelman B, Eggelbusch M, Huijts JY, Noort W, Hendrickse PW, Bloemers FW, Posthuma JJ, van Amstel P, Goulding RP, Degens H, Jaspers RT, van Vugt M, Wüst RCI. Skeletal muscle properties in long COVID and ME/CFS differ from those induced by bed rest. Nat Commun. 2026 Jul 28;17(1):9125. doi: 10.1038/s41467-026-75725-y. PMID: 42649155. https://www.nature.com/articles/s41467-026-75725-y (Full text)

Raman Spectroscopy Combined with Machine Learning Reveals Myalgic Encephalomyelitis–Associated Biomolecular Signatures at Rest and After Standardized Stress

Abstract:

Myalgic encephalomyelitis (ME) is characterized by profound fatigue, post-exertional malaise (PEM), and cognitive dysfunction. Despite its clinical significance, the pathophysiology of PEM and disease heterogeneity remain unclear, and no validated biomarkers are available for rapid diagnosis or monitoring. We aimed to develop a screening approach combining label-free Raman spectroscopy (RS) and machine learning modeling (ML) to detect biomolecular changes in blood plasma and differentiate patients with ME from sedentary healthy controls.
Blood plasma was collected from 115 patients with ME and 45 controls at rest (T0) and 90 min after a standardized, non-invasive stress test designed to induce PEM. Plasma samples were analyzed by RS, and ML models were developed independently at each time point to differentiate patients with ME and controls.
The RS-ML models identified spectral features consistent with contributions from proteins, lipids, and low-molecular-weight metabolites. At T0 and T90, the area under the receiver operating characteristic curve, accuracy, specificity and sensitivity were 0.85 and 0.83, 79% and 84%, 82% and 90%, and 73% and 69%, respectively. RS-ML provides a rapid, low-cost approach to detect ME-associated biomolecular signatures in plasma and capture biochemical alterations associated with standardized stress.
Source: Heidarifard M, Moezzi A, Dallaire F, Ember K, Elremaly W, Caraus I, Franco A, Leblond F, Moreau A, Dehaes M. Raman Spectroscopy Combined with Machine Learning Reveals Myalgic Encephalomyelitis–Associated Biomolecular Signatures at Rest and After Standardized Stress. International Journal of Molecular Sciences. 2026; 27(11):4937. https://doi.org/10.3390/ijms27114937 https://www.mdpi.com/1422-0067/27/11/4937 (Full text)

Irisin Signaling Resistance in Myalgic Encephalomyelitis: A Proposed Mechanistic Framework for Post-Exertional Malaise Involving the TSP-1-HSP90α-αvβ5 Axis

Abstract:

Myalgic Encephalomyelitis (ME) is a chronic, multisystem disease characterized by systemic metabolic dysfunction and post-exertional malaise (PEM). In this study, we investigated the dysregulation of irisin, an exercise-induced myokine, and its potential antagonism by thrombospondin-1 (TSP-1).

In a cross-sectional study (92 ME patients vs. 44 sedentary healthy controls), plasma irisin and TSP-1 levels were measured at baseline and after a 90 min mechanical stress challenge applied to induce PEM. ME patients exhibited significantly lower baseline irisin (p < 0.05) and a blunted exertional response (p < 0.05). Paradoxically, baseline irisin was an independent predictor of fatigue severity (β = 0.728, p = 0.018), with moderate-to-severe patients showing elevated levels of both irisin and TSP-1 (p < 0.05), suggesting a compensatory but ineffective response. Functional cellular dielectric spectroscopy indicated that TSP-1 inhibits irisin signaling in a concentration-dependent manner. Irisin signaling was markedly reduced by both αvβ5 blockade and HSP90α inhibition in this experimental system, consistent with a diminished ability to counteract TSP-1.

Collectively, these findings support a model in which dysregulation of the irisin-TSP-1 axis contributes to metabolic dysfunction in ME. Elevated circulating TSP-1 levels are associated with symptom severity and are linked to impaired irisin signaling in an HSP90α- and αvβ5-dependent context. This interaction is consistent with defective metabolic adaptation and highlights a potential therapeutic target that warrants further validation to restore energy homeostasis.

Source: Souma B, Elremaly W, Akoume MY, Elbakry M, Godbout C, Moreau A. Irisin Signaling Resistance in Myalgic Encephalomyelitis: A Proposed Mechanistic Framework for Post-Exertional Malaise Involving the TSP-1-HSP90α-αvβ5 Axis. Int J Mol Sci. 2026 May 26;27(11):4770. doi: 10.3390/ijms27114770. PMID: 42278300. https://www.mdpi.com/1422-0067/27/11/4770 (Full text)

Is the RACGP HANDI recommendation of incremental physical activity for chronic fatigue syndrome/myalgic encephalomyelitis harming patients?

Opinion:

In April 2024, The Royal Australian College of General Practitioners (RACGP) Handbook of Non-Drug Interventions (HANDI)committee published a guideline: Incremental physical activity for chronic fatigue syndrome/myalgic encephalomyelitis.1 The HANDI committee claims to recommend interventions that are based on ‘solid evidence’.2 But is this always the case?

An evaluation under the AGREE II instrument for assessing guidelines scored the RACGP guideline at only 2% for rigour of development.3 Alarmingly, the guideline provides no evidence of a systematic review of the literature, nor an analysis of the strengths and limitations of the three cited papers: the PACE trial; the Cochrane review, Exercise therapy for chronic fatigue syndrome; and Fawzy et al’s systematic review of treatments for post-acute COVID-19 syndrome [PACS]).1,4,5,6 Indeed, the PACE trial has been heavily criticised for outcome switching and bias.7–9 If the PACE trial had adhered to the original definition of recovery laid out at the beginning of the study, only 4% of graded exercise therapy participants would have been classified as recovered, and the effect would not have been statistically significant.9 After participants had completed therapy, the study’s authors weakened the definition of recovery to encompass values that fall far below healthy norms. In fact, many ‘recovered’ participants were still sick enough to meet the entry requirements to the study.8 Worse, some participants were classified as recovered or improved before undertaking any treatment.10

Read the rest of this article HERE>>

Source: Jacqueline Stallard Stephan Praet Sandeep Gupta Angela Smith. Is the RACGP HANDI recommendation of incremental physical activity for chronic fatigue syndrome/myalgic encephalomyelitis harming patients? AJGP, Viewpoint​
Volume 55, Issue 3, March 2026. https://www1.racgp.org.au/ajgp/2026/march/is-the-racgp-handi-recommendation-of-incremental-p (Full text)

Inefficient energy consumption is related to post exertional malaise during cardiopulmonary exercise testing in long COVID

Abstract:

Background: Dyspnea, fatigue and post-exertional malaise (PEM) are hallmark features of long Covid and emerging evidence suggests that abnormal energy metabolism may contribute to these symptoms. A cardiopulmonary exercise test (CPET) provides a detailed physiologic assessment of ventilatory and cardiovascular function and can offer insights into metabolic substrate utilization energy at rest and during exertion. Our aim was to evaluate patterns of energy metabolism at rest and during exercise during a CPET in patients with long Covid.

Methods: We conducted a cross-sectional study of consecutive non-selected patients that had been referred for a CPET. We included two groups: a long COVID and a control group. The CPET was performed on a cycle ergometer and we measured standard variables including oxygen uptake (V̇O₂), respiratory exchange ratio (RER), breathing reserve, heart rate, O2 pulse, and anaerobic threshold. We used RER to calculate indirect calorimetry estimating the use of carbohydrates and fat at rest and exertion. We analyzed the association between long COVID symptom severity symptoms including fatigue and post-exertional malaise (PEM) with patterns of energy consumption. We used logistic regression and area under the receiver operating characteristic curve to determine which CPET variables were most associated with long COVID.

Results: CPET results were analyzed for 50 patients who met the definition of long COVID and 45 patients controls. Long COVID patients and controls had similar peak V̇O₂, heart rate on exertion and V̇O₂ at anaerobic threshold. Seventy-three percent of patients with long COVID had predominant energy use of carbohydrates rather than fat at rest compared to 20% of controls. In multivariable models the odds ratio of using fat as energy source at rest was 0.99; 95% CI 0.99–0.99; p = 0.04. Patients with long COVID and severe fatigue as well as severe PEM had higher usage of carbohydrates (p < 0.01) and similar use of fat.

Conclusion: Patients with long COVID use energy inefficiently and this pattern could serve as a diagnostic feature in certain presentations of long COVID.

Source: Leonardo Tamariz, Brian Garnet, Santiago Avecillas et al. Inefficient energy consumption is related to post exertional malaise during cardiopulmonary exercise testing in long COVID, 15 December 2025, PREPRINT (Version 1) available at Research Square [https://doi.org/10.21203/rs.3.rs-8072121/v1] https://www.researchsquare.com/article/rs-8072121/v1 (Full text)

Temporal dynamics of the plasma proteomic landscape reveals maladaptation in ME/CFS following exertion

Abstract:

The overarching symptom of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is post-exertional malaise (PEM), an exacerbation of symptoms following physical or mental exertion. To investigate the molecular underpinnings of PEM, we performed longitudinal plasma proteomics using the Somascan® 7K aptamer-based assay to monitor 6,361 unique plasma proteins in 132 individuals (96 females and 36 males) subjected to two maximal cardiopulmonary exercise tests separated by a 24-hour recovery period.

The cohort included 79 ME/CFS cases compared to 53 age- and BMI-matched sedentary controls, allowing us to distinguish disease-specific molecular alterations from those due to physical deconditioning. Longitudinal profiling revealed widespread proteomic changes following exertion, with the most pronounced alterations observed in ME/CFS participants during the recovery phase, coinciding with the onset of PEM.

Compared to controls, ME/CFS subjects showed persistent dysregulation of immune, metabolic, and neuromuscular pathways. Key findings included suppression of T and B cell signaling, downregulation of IL-17 and cell-cell communication pathways, and upregulation of glycolysis/gluconeogenesis, suggestive of mitochondrial stress and impaired immune recovery from exercise. Proteomic associations with physiological performance (VO2max, anaerobic threshold) revealed disruptions between protein abundance and exercise capacity in ME/CFS versus controls.

Correlations with symptom severity linked changes in immune-related proteins and ME/CFS symptoms including muscle pain, recurrent sore throat, and lymph node tenderness. Sex-stratified analyses revealed distinct molecular responses between females and males, emphasizing the importance of considering sex as a biological variable in ME/CFS research.

Finally, our analysis of sedentary controls contributes new data of molecular responses to acute exertion in a predominantly female sedentary cohort, a population historically underrepresented in exercise physiology studies. Together, these findings underscore the value of dynamic, proteomic profiling over time for characterizing maladaptive responses to exertion in ME/CFS and provide a foundation for deeper mechanistic investigation into PEM.

Source: Germain A, Glass KA, Eckert MA, Giloteaux L, Hanson MR. Temporal dynamics of the plasma proteomic landscape reveals maladaptation in ME/CFS following exertion. Mol Cell Proteomics. 2025 Nov 12:101467. doi: 10.1016/j.mcpro.2025.101467. Epub ahead of print. PMID: 41237904. https://www.mcponline.org/article/S1535-9476(25)00566-3/fulltext (Full text)

Abnormal breathing patterns and hyperventilation are common in patients with chronic fatigue syndrome during exercise

Introduction: Patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) experience symptoms of fatigue, dyspnea, mental fog, and worsening fatigue after physical or mental efforts. Some of these patients have been found to hyperventilate. In long COVID patients, many of whom also have ME/CFS, dysfunctional breathing (DB) has been described. Whether patients with ME/CFS, independent of COVID-19, experience dysfunctional breathing is unknown, as well as how it may relate to hyperventilation.

Methods: We performed serial 2-day cardiopulmonary exercise testing (CPET) in 57 patients with ME/CFS and 25 age- and activity-matched control participants. Peak oxygen consumption (VO2), ventilatory efficiency slope (VE/VCO2), O2 saturation, end-tidal CO2 (PetCO2), heart rate, and mean arterial blood pressure were measured in all patients during upright incremental bicycle exercise. Ventilatory patterns were reviewed using minute ventilation (VE) versus time, respiratory rate, and tidal volume versus minute ventilation graphs. Chronic hyperventilation (HV) was defined as a PETCO2 of <34 mm Hg that persisted during low-intensity exercise. Dysfunctional breathing was characterized by a 15% increase in oscillations in minute ventilation during at least 60% of the exercise duration or by a scatterplot pattern of respiratory rate and tidal volume plotted versus minute ventilation.

Results: The patients with ME/CFS had an average age of 38.6 ± 9.6 years, and a mean body mass index (BMI) of 24.1 ± 3.4, which was comparable to the sedentary controls. All participants performed maximal exercise, achieving a respiratory exchange ratio (RER) of >1.05. For the patients with ME/CFS, peak VO2 averaged 22.3 ± 5.3 mL/kg/min, which was 79 ± 20% of predicted and comparable to that observed in the sedentary controls (23.4 ± 4.6 mL/kg/min; 81 ± 12%; p = NS). A total of 24 patients with ME/CFS (42.1%) met the criteria for dysfunctional breathing compared to four sedentary controls (16%) (p < 0.02). In total, 18 patients with ME/CFS (32%) had hyperventilation compared to one sedentary control participant (4%) (p < 0.01), and nine patients with ME/CFS had both hyperventilation and dysfunctional breathing, whereas no sedentary participant exhibited both. The patients with ME/CFS and hyperventilation had significantly higher VE/VCO2 ratios (HV+: 34.7 ± 7.2; HV−: 28.1 ± 3.8; p < 0.001). A total of 15 of 18 patients with hyperventilation (83%) had either elevated VE /VCO2 ratios (n = 15) or dysfunctional breathing (n = 9) compared to 44% (n = 17) of the 40 non-hyperventilators (p < 0.01).

Conclusion: Dysfunctional breathing and hyperventilation are common in patients with ME/CFS and could present a new therapeutic target for these patients.

Source: Mancini Donna M. , Brunjes Danielle L. , Cook Dane , Soto Tiffany , Blate Michelle , Quan Patrick , Yamazaki Tadahiro , Norweg Anna , Natelson Benjamin H. Abnormal breathing patterns and hyperventilation are common in patients with chronic fatigue syndrome during exercise. Frontiers in Medicine, Volume 12 – 2025. DOI=10.3389/fmed.2025.1669036. ISSN=2296-858X https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2025.1669036 (Full text)