#PeeNee2 on X wrote:
New preprint #RobWust + team
"our observations suggest intrinsic skeletal muscle abnormalities contribute to limited exercise capacity, including reduced capillary supply relative to muscle fiber size and mitochondrial impairments."
medRxiv · Skeletal muscle properties in long COVID and ME/CFS differ from those induced by bed restPatients with long COVID and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) suffer from a reduced exercise capacity, skeletal muscle abnormalities and post-exertional malaise (PEM), where symptoms worsen with cognitive or physical exertion. PEM often results in avoidance of physical activity, resulting in a lower aerobic fitness, which may contribute to skeletal muscle abnormalities. Here, we compared whole-body exercise responses and skeletal muscle adaptations after strict 60-day bed rest in healthy people with those in patients with long COVID and ME/CFS, and healthy age- and sex-matched controls. Bed rest altered the respiratory and cardiovascular responses to (sub)maximal exercise, while patients exhibited respiratory alterations only at submaximal exercise. Bed rest caused muscle atrophy, and the reduced oxidative phosphorylation related to reductions in maximal oxygen uptake. Patients with long COVID and ME/CFS did not have muscle atrophy, but had less capillaries and a more glycolytic fibers, none of which were associated with maximal oxygen uptake. While the whole-body aerobic capacity is similar following bed rest compared to patients, the skeletal muscle characteristics differed, suggesting that physical inactivity alone does not explain the lower exercise capacity in long COVID and ME/CFS
### Competing Interest Statement
The authors have declared no competing interest.
### Funding Statement
This study was supported the Patient-Led Research Collaborative for Long COVID, the AMC and VU foundation, ZonMw Onderzoeksprogramma for ME/CVS, the Solve ME 2022 Ramsay Grant Program, ME Research UK, ME Stars of Tomorrow Scholarship award from the ICanCME Research Network (to B.T.C.), and Stichting Long COVID Nederland.
### Author Declarations
I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.
Yes
The details of the IRB/oversight body that provided approval or exemption for the research described are given below:
Ethics committee of Amsterdam UMC, Medical Association North Rhine (number 2018143) and NASA (Johnson Space Center, Houston, United States) gave ethical approval for this work.
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I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.
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All data produced in the present study are available upon reasonable request to the authors