Fatigue and difficulty with exertion in people with long COVID and ME/CFS (myalgic encephalomyelitis/chronic fatigue syndrome) are not simply the result of poor physical condition.
This is the conclusion of new research from Vrije Universiteit Amsterdam and Amsterdam UMC.
In the study, movement scientists compared muscle changes in people with long COVID and ME/CFS to those in healthy individuals who underwent 60 days of bed rest. All groups had less energy and a reduced ability to perform physical tasks—but the underlying causes were different.
“Patients are often told they're just out of shape,” says Rob Wüst, VU movement scientist and lead researcher. “Our results show that this is incorrect. The muscle changes in these patients are different from what we see in healthy people after prolonged inactivity.”
Key findings
- No muscle wasting in patients, while healthy individuals showed clear muscle loss (atrophy) after bed rest.
- Changes in muscle fibers: Patients had fewer “slow-twitch” fibers, which are essential for endurance, and more “fast-twitch” fibers, which tire quickly.
- Impaired energy production in muscles due to malfunctioning mitochondria—the energy factories of our cells.
- Fewer capillaries in the muscles of ME/CFS patients, which may explain why they feel worse after exertion (post-exertional malaise).
What does this mean?
These findings demonstrate that it is incorrect to assume that people with long COVID or ME/CFS mainly suffer due to being less active. Their muscles function differently, and this must be taken into account during treatment and rehabilitation.
The researchers therefore call for new, adapted rehabilitation programs that are better aligned with the actual biological processes at play in these patients.
The research was supported by ZonMw, Solve ME, ME Research UK, and the Patient-Led Research Collaborative.