Muscle abnormalities worsen after post-exertional malaise in long COVID, 2023/4, Wüst, van Vugt, Appelman et al

Andy · Feb 19, 2025

Referring to

This is a reply to this communication, Should we be careful with exercise in post-exertional malaise after long COVID?, 2025, Saris et al

SNT Gatchaman · Feb 18, 2025

That's another great response from the team.

Deconditioning has been proposed as causative of skeletal muscle changes in Long COVID patients. Our previous work on bed rest demonstrates that adaptations in skeletal muscle structure and function differ markedly between Long COVID patients and healthy persons exposed to severe deconditioning. Bed rest induces rapid muscle atrophy and loss of capillarization, which was not observed in our Long COVID patients. We did not observe alterations in fiber type composition after 60 days of strict bed rest, whereas our Long COVID patients exhibited a more glycolytic phenotype. Our Long COVID participants showed lower mitochondrial respiration, due to mitochondrial dysfunction rather than mitochondrial loss, the latter of which is more typically seen after long-term bed rest. The absence of a correlation between and succinate dehydrogenase activity also suggests that factors other than deconditioning contribute.
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We do not know the underlying factors contributing to these changes, and as good scientific practice, we refrained from drawing causal relationships in our publication. We were therefore surprised to read that Saris et al. drew such conclusions based on work which was not set up to be causal in nature.
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Saris et al. suggest that atrophied fibers cannot occur one-day following exercise, but the reference they provide proves the opposite.
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Muscle abnormalities worsen after post-exertional malaise in long COVID, 2023/4, Wüst, van Vugt, Appelman et al

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Muscle abnormalities worsen after post-exertional malaise in long COVID, 2023/4, Wüst, van Vugt, Appelman et al

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