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Muscles

Wust asked what an intense aerobic workout would do to the muscles in ME/CFS.

The chronic fatigue syndrome (ME/CFS) and fibromyalgia fields have produced some good muscle studies, but a recent study, “Muscle abnormalities worsen after post-exertional malaise in long COVID,” was something else indeed. The study leader, Rob Wust, has a double doctorate in muscle physiology and has been particularly interested in exercise intolerance, mitochondrial bio-energetics, and muscle metabolism.

Thus far, Wust has published three papers on muscle abnormalities in long-COVID patients. The first study of ICU COVID-19 patients found muscle fiber atrophy, metabolic alterations, and immune cell infiltration.

It was the second study, though, that really opened some eyes. This study—which was funded by a variety of sources, including the Patient-Led Research Collaborative for Long COVID and the Solve M.E.’s 2022 Ramsay Grant Program—did something simple but brilliant: it took muscle biopsies from long-COVID patients, put the patients on a bike and exercised them to exhaustion, and then took a second round of muscle biopsies, and dug into them.

The Results

The cardiopulmonary results were pretty typical – a reduction in energy production (VO2 max, peak power output), altered breathing patterns (possibly hyperventilation), plus the near-infrared spectroscopy readings found a reduction in “peripheral O2 extraction”; i.e. oxygen (read energy) was not being taken up by the muscles in normal amounts.

And how about those muscles? What happens to muscles when they’ve been worked hard but haven’t gotten normal amounts of oxygen (energy)? It turned out that a lot happened. The most obvious explanation – low levels of blood vessels feeding the muscles – didn’t pan out, as the ME/CFS patients had plenty of blood vessels (capillaries) feeding their muscles.

That suggested that the problems lay in the muscles themselves. Indeed, higher levels of glycolytic, type II muscle fibers that provide short bursts of energy but stink at endurance in the longCOVID patients provided one reason for their poor performance on the bicycle.  Lower levels of an enzyme called succinate dehydrogenase (SDH) that activates the mitochondria provided another reason mitochondrial energy (ATP) production fell short.

Glycolysis

Wust – like past ME/CFS studies – found that the long-COVID patients relied more on glycolytic or anaerobic energy production than normal.

Increased levels of metabolites associated with anaerobic energy production and a dearth of metabolites associated with aerobic energy production also suggested that the powerful aerobic energy production pathway had been silenced. The anaerobic rout continued with reduced ratios of citric acid (mitochondria) to lactate (result of glycolysis/anaerobic energy production) levels.

Again and again, the study found that during exercise, the long-COVID patients relied more on the primitive, inefficient, and ultimately toxic form of anaerobic energy production. That’s primitive, as in this form of energy production evolved before oxygen showed up in our atmosphere. We keep it around because it produces short bursts of energy. Anything longer than that and it runs out of gas and starts producing toxic metabolites like lactate.

The list went on – lower creatine levels, problems with lipid synthesis, high levels of oxidative stress, high levels of atrophied or dead muscle fibers with evidence of immune invasion – indicating the immune system may have attacked the muscles.

Rob Wust told the Guardian:

“It’s really confirming that there is something inside the body going wrong with the disease. It damages your muscles, it worsens your metabolism, and it can explain why you feel muscle pain and fatigue up to weeks after the exercise,”

All in all, the paper provided a gripping explanation from the perspective of the muscles of why physical exercise is so problematic in ME/CFS. As such, it HAD to be rebutted – and it was – but that’s for later in the blog. Next came the exposition paper that attempted to put the pieces together.

The Exposition Paper

In December 2024, Braeden Charlton, Rob Wust, and colleagues published a paper, titled “Skeletal muscle adaptations and post-exertional malaise in long COVID,” that explains what they think has happened to the muscles of long-COVID patients, and probably people with ME/CFS. They listed five possibilities (and rejected one).

Deconditioning – There is no doubt that in the more severely ill, deconditioning adds an exacerbating factor, but the authors noted there is no evidence that it’s causing the illness. (See “the Reply to the Reply” below for more on this).

Hypoxia refers to low oxygen levels. If the oxygen isn’t getting to the cells, they’ll turn to alternative means of producing energy: glycolysis and anaerobic energy production, which studies show is happening in these diseases. Note that ample amounts of oxygen are present in the blood but are not, in a subset of patients, being taken up in the muscles.

Mitochondria

Mitochondrial problems could explain the reduced energy production found.

The bigger question is, “What is causing this?” The authors proposed mitochondrial problems that prevent oxygen from being taken up; problems diffusing oxygen into the muscles from the capillaries, caused by capillary blockage; a thickened extracellular matrix that surrounds the capillaries that prevents oxygen from getting out; or amyloid clots that are causing endothelial damage.

Autoimmunity and “Electrophysiological alterations” – It’s possible that β-adrenergic receptors (β2-ARs) could impair blood flows and impact the mitochondria. Allied with this idea is the possibility that increased muscle sodium content (which has nothing to do with diet) may be eating up ATP and causing intracellular calcium overloads, which further smack the mitochondria. (A blog on this is coming up.)

Central fatigue – where the brain turns off muscle activity is another, more distant, possibility.

The problem with the low oxygen uptakes lies between the arteries and the muscles, leaving, if I have it right, two basic targets – the mitochondria and the blood vessels.

An ME/CFS Interlude

Systrom’s invasive exercise studies found that the exertion problems in long COVID are nearly identical to those in ME/CFS. His studies suggest that blood may be shunted from the arteries into the veins before it reaches the muscles in some patients. In other patients, the veins are not constricting enough to deliver normal amounts of blood to the heart – preventing it from pumping enough blood to the muscles. Systrom also has uncovered evidence suggesting that the enzymes needed to power the aerobic energy production process may be inhibited.

Perhaps because they haven’t been studied in long COVID but have in ME/CFS, Wust et al. didn’t mention low blood volume, or the failure of ME/CFS patients to respond on a molecular level (gene expression, epigenetics, metabolomics, proteomics) during and after exercise.

While low blood volume does not appear to be a major factor, it is a factor. Systrom has found that adding saline IVs does improve energy production. A case report from Workwell found that regular use of saline IVs substantially improved one patient’s functioning.

Likewise, hyperventilation (rapid, deep breathing) found in some long-COVID and ME/CFS patients could activate the sympathetic nervous system which, by narrowing the blood vessels, could reduce blood flows to the muscles.

The Exercise Intolerance in POTS, ME/CFS and Fibromyalgia Explained?

Affirmation

Wust’s “Muscle abnormalities worsen after post-exertional malaise in long COVID” study produced a stunning affirmation of ME/CFS and long-COVID patients’ experiences with intense exercise.

Key

Exercise studies have played a key role in explaining these diseases.

From the beginning of my ME/CFS as a young man, it’s been the post-exertional malaise that stood out for me. While the day-to-day fatigue and pain kept me from functioning like I used to, my symptoms were kind of general and hard to explain. I was very, very tired, I was in pain, I felt like lying down much of the time, I had trouble concentrating, wasn’t sleeping well, etc.

Because these were symptoms that everyone experienced from time to time but were magnified greatly, they weren’t much to bite onto. It was a different story when I exercised, though.

Exercise had been an important part of my life, but now exercise produced an explosion of symptoms, some of which I’d never encountered before. Along with the increased fatigue and pain, came the heart pounding, the intense burning muscle pain, the feeling of contracted muscles, a weird sensation of thickened skin, dizziness, irritability, etc..Those symptoms really stood out.

From the beginning, I thought exercise studies would play a key role in explaining ME/CFS, and over time, through the work of Workwell, Systrom, Keller, Vermeulen, Cook, Hanson, Newton and others, they have been. The good news is that the Dutch team’s muscle findings (reduced aerobic energy production, increased reliance on anaerobic energy production, and others) in long COVID are in line with that past work.

Last Gasp of the Biopsychosocial Crowd?

However, they were a bridge too far for Bridget Ranque and 16 other researchers, who attempted to dismiss the study findings in “Reply: Muscle abnormalities in Long COVID.”

man running

The study finding that very intense exercise harms the muscles does not mean that less intense forms of exercise will necessarily do the same. (Image from Gerald_Altman_Pixabay)

The authors did have one legitimate concern: their worry that long-COVID patients will misinterpret the findings and conclude that any exercise will harm them. As Wust noted, his study needs to be taken in context: it exposed long-COVID patients to a short but very intense exercise session that is literally designed to drive them into a state of muscular exhaustion. I remember during a similar exercise study my legs literally stopped moving the pedals. I have never engaged in that kind of exercise outside of an exercise study.

The GIST

  • The ME/CFS and fibromyalgia fields have produced some good muscle studies, but a recent study, “Muscle abnormalities worsen after post-exertional malaise in long COVID,” was something else indeed.
  • The study found that aerobic energy production – the kind that relies on oxygen uptake – was inhibited in various ways. Higher levels of glycolytic, type II muscle fibers. lower levels of an enzyme called succinate dehydrogenase (SDH) that activates the mitochondria, increased levels of metabolites associated with anaerobic energy production, and reduced ratios of citric acid (mitochondria) to lactate (result of glycolysis/anaerobic energy production) levels all pointed to an energy production system that was overly dependent on the primitive and inefficient anaerobic energy production system.
  • High levels of oxidative stress, atrophied or dead muscle fibers, and signs of immune invasion suggested that the short but very intense period of exercise had directly damaged the muscles.
  • In 2024, the authors published a paper proposing 5 possible explanations for muscle problems found in long-COVID patients.
  • After rejecting deconditioning, they concluded that low oxygen uptake to the muscles caused by mitochondrial problems and/or reduced blood flows to the muscle cells, an autoimmune reaction that impairs both blood flows to the muscles and/or mitochondrial activity, and/or problems originating in the brain (central fatigue) were likely impacting the muscles.
  • ME/CFS studies suggest something similar is happening and add in additional factors such as low blood volume, hyperventilation, and the failure of ME/CFS patients to respond appropriately on a molecular level (gene expression, epigenetics, metabolomics, proteomics) to exercise.
  • Recently, 16 researchers, many of whom are allied with the biopsychosocial field, attempted to dismiss Wust’s findings in a “Reply” to the study. They asserted that deconditioning produced the findings, that the symptom exacerbation seen in the ME/CFS patients was a normal response to exercise, and that the patient’s pathological response to their symptoms played a role.
  • Wust showed that the ME/CFS patients had activity levels similar to the controls—and to the average American—that the symptoms produced were not normal, that numerous findings of the study were either not associated or, indeed, were opposite to those found in deconditioning.
  • The biopsychosocialists arguments seem to be becoming ever more shrill and less convincing. For instance, Beatrice Ranque, the lead author of the reply, concluded that because normal physical examinations and routine test results suggest that “no organic impairment” exists in long COVID, psychological factors must be important.
  • Meanwhile, at least five more muscle studies are underway in ME/CFS and long COVID-19, and a recently published invasive exercise study provided more insights into the pathophysiology of long COVID-19. A blog on that is coming up.

Wust’s results do not reflect what happens to the muscles when small bouts of exercise—from walking to cleaning to stretching to lifting small weights—are engaged in

Workwell’s post-exercise symptom assessment of patients after their two-day exercise test for disability indicated ME/CFS patients who are in good enough shape to take the test invariably recover within a period of time. When David Systrom’s patients reach a certain level, he recommends his patients start an exercise regimen. Similarly, Health Rising recently ran a recovery story where Lucinda Bateman instituted an exercise regimen using sit-ups and low weights in a patient when he reached a certain level. I stayed away from weights for decades but now find that using exercise bands in short bursts is helpful. D. Hupin, one of the co-authors, found that personalized strength and endurance training, which did not result in PEM, was helpful in long COVID.

In his “Reply: Muscle abnormalities in Long COVID” Wust so easily wiped away the rest of their concerns as to make their “reply” seem like it was borne out of desperation.

Deconditioning? It was like déjà vu all over again (:)) when the authors trotted out the old and tired deconditioning trope. Because the patients were deconditioned, the authors asserted, the short but intense exercise regimen was going to produce muscle damage.

Wust pointed out that the long-COVID patients exhibited the same activity level as the healthy controls (5,181 vs. 4,727 steps/day for patients and controls, respectively) – about the same activity level (rather sadly) as the average person in the U.S.

Several physiological findings demonstrated that something different from deconditioning was at work: the different skeletal muscle alterations, the opposite mitochondrial substrate utilization (more carbohydrates), and the abnormal muscle findings found before the exercise intervention. The significantly lower gas exchange thresholds and respiratory compensation points indicated that effort was not a problem.

If Wust had included findings from ME/CFS, he could have added more objections. The deconditioning hypothesis originally turned on the fact that low stroke volumes were found in ME/CFS. Still, Van Campen et al. found that everyone with ME/CFS -whether they were bedbound or active – had similarly low stroke volumes, indicating that while low stroke volumes are part of the disease, they are not the result of being inactive.

Since everyone experiences muscle pain after exercise, what’s the big deal about muscle pain in the ME/CFS patients? Seeing this objection come out of the pens of some long-time ME/CFS researchers – who well know that PEM produces many other symptoms – was kind of sad.

The patients’ experience of their symptoms caused their distress. The authors used the Nath ME/CFS intramural study to conclude that the patients’ “experience of symptoms” and altered interoception, allostatic load, and perceived burden explained their response.

Wust pointed out, though, that the Nath paper did not explore any of those topics and, in fact, provided “multiple physiological explanations for ME/CFS pathophysiology, including autonomic dysfunction, differential cerebrospinal fluid catecholamines, and metabolite profiles, and lower post-exercise cortisol responses”. Plus, it confirmed Wust’s findings of lower °𝑉⁢𝑂2⁢max and impairments in skeletal muscle mitochondrial metabolism”.

“Ranque” Desperation?

The biopsychosocialists are still out there, but seem to be more of a fringe element, and their arguments seem to be becoming ever more shrill and less convincing. Take Beatrice Ranque, the lead author of the reply to Wust. In “Why the hypothesis of psychological mechanisms in long COVID is worth considering,” she fell back on the weak argument that because normal physical examinations and routine test results suggest that “no organic impairment” exists in long COVID, psychological factors must be important.

She hit that theme again when she pointed out that “self-reported persistent symptoms poorly correlate with objective long-term organ damage”, and when she wrote because “debilitating and persistent symptoms…are not fully explained by damage of the organs“, therapeutic interventions should follow those recommended for “functional somatic disorders”. Her conclusions – which completely ignored the molecular findings in long COVID – were embarrassing in a disease as new and poorly studied as long COVID.

It’s no wonder, though, that Ranque was so bothered by a study that found plenty of “organic impairment”. With objections like Ranque et al.’s to the Appleman/Wust long-COVID study, people with long COVID and ME/CFS have little to worry about – and indeed, with a mess of ME/CFS and long-COVID muscle studies coming up, things are probably not going to get any easier for them.

Skeletal muscle

More muscle studies are underway.

Upcoming Muscle Studies

Two major ME/CFS muscle studies funded by the Open Medicine Foundation are underway. One will take a deep, deep dive (genomics, proteomics, metabolomics, phospho-proteomics, ultrastructural analysis, mitobiogenetic markers) into muscle samples from ME/CFS patients. The other will take muscle samples before and after a two-day CPET exercise test and, among other things, assess levels of citrate synthase (which Systrom has found depleted in ME/CFS before), gene expression, metabolites, and proteins in the muscles.

Plus, Paul Hwang of NHLBI and Avindra Nath are continuing to collaborate on their WASF3 muscle cell findings. Rob Wust’s Solve M.E. Ramsay award examines muscle biopsies before and after exercise in ME/CFS, and David Cosgrove at Cornell scored an NIH grant to analyze ME/CFS muscle biopsies using new technologies to “identify changes in cell-cell communication (ligand-receptor) pathways involving myogenic, endothelial, and immune cells and their spatial organization between control and ME/CFS muscles” and assess the role blood vessels play.

Things are moving quickly. Last November, Leitner and Singh took invasive exercise testing to a new level in long COVID. A blog on that study is coming up.

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