Reduced exercise capacity and muscle symptoms in people with post-COVID and ME/CFS (Myalgic Encephalomyelitis/Chronic Fatigue Syndrome) cannot simply be explained by poor physical fitness or prolonged inactivity. The muscles of these patients function differently in several respects from those of healthy people who have been inactive for a prolonged period. This is shown by new research from Vrije Universiteit Amsterdam and Amsterdam UMC. The study results were published today in Nature Communications.

Source: Amsterdam UMC

Exercise scientist and co-principal investigator Rob Wüst of Vrije Universiteit Amsterdam explains: “There are indications of abnormalities in muscle fibres, energy production and oxygen supply. Our study highlights that patients with post-COVID and ME/CFS should not be treated as if they have simply lost physical fitness. Future diagnostics and rehabilitation should take this into account.”

In the study, the researchers compared people with post-COVID and ME/CFS with a group of healthy people who had undergone 60 days of strict bed rest. Although all groups showed reduced exercise capacity, the underlying changes in their muscles were clearly different.

“Patients are often told that they are simply out of shape,” says Wüst. “Our results show that this explanation is too simplistic. The muscles of patients with post-COVID and ME/CFS show different changes from those of healthy people after prolonged bed rest.”

Impaired energy production

After 60 days of bed rest, the healthy participants showed clear muscle loss. This general muscle wasting was not observed in patients with post-COVID and ME/CFS. Instead, the researchers found other abnormalities in the muscles of patients. Compared with healthy controls, both patient groups had fewer slow-twitch muscle fibres, which are important for endurance. They also had relatively more fast-twitch muscle fibres, which fatigue more quickly.

The researchers also found signs of impaired energy production in the muscles. Mitochondria, often described as the powerhouses of the cell, functioned less effectively in patients with post-COVID and ME/CFS. In patients with ME/CFS, fewer capillaries were also found around the muscle fibres, which may contribute to reduced oxygen supply during exercise.

Implications for treatment and rehabilitation

The findings are important for how exercise-related symptoms in post-COVID and ME/CFS are understood. The results show that these symptoms cannot simply be explained by reduced physical activity or loss of fitness. The muscles of patients function differently in several respects from those of healthy people who have been inactive for a prolonged period.

According to the researchers, this means that treatment and rehabilitation should be better tailored to the biological abnormalities found in these patients. Standard exercise programmes based on the assumption of ordinary deconditioning may not be appropriate for people with post-COVID or ME/CFS. This is particularly relevant for patients experiencing post-exertional malaise: a worsening of symptoms following physical or mental exertion.

This research was conducted by researchers from Vrije Universiteit Amsterdam and Amsterdam UMC, in collaboration with international partners. The study was supported in part by ZonMw, Solve ME, ME Research UK and the Patient-Led Research Collaborative.

Read more about the full study in the scientific journal Nature Communications.