The reduced exercise capacity and muscle symptoms experienced by people with post-COVID and ME/CFS (Myalgic Encephalomyelitis/Chronic Fatigue Syndrome) cannot be explained simply by poor physical fitness or prolonged inactivity.
The muscles of these patients function differently in several ways compared to those of healthy people who have been inactive for a long time. This is according to new research by Vrije Universiteit Amsterdam and Amsterdam UMC published in Nature Communications.
Principal investigator and movement scientist Rob Wüst of Vrije Universiteit Amsterdam explains: “There are indications of abnormalities in muscle fibers, energy production, and oxygen supply. “Our study underscores that patients with post-COVID and ME/CFS should not be treated as if they have merely lost their fitness,” says Wüst. “Future diagnostics and rehabilitation must take this into account.”
In the study, researchers compared people with post-COVID and ME/CFS to a group of healthy individuals who had been on strict bed rest for 60 days. Although all groups had lower endurance, the underlying muscle changes turned out to be distinctly different.
“Patients are often told that they’ve mainly lost their fitness,” says Wüst. “Our results show that this view is too simplistic. The muscles of patients with post-COVID and ME/CFS exhibit different changes than those of healthy people after prolonged bed rest.”
Impaired Energy Production
After sixty days of bed rest, healthy subjects showed significant muscle loss. In contrast, patients with post-COVID and ME/CFS did not exhibit this general muscle wasting. However, the researchers did find other abnormalities in the patients’ muscles. For example, compared to the healthy control group, both patient groups had fewer slow-twitch muscle fibers, which are important for endurance. They also had a relatively higher proportion of fast-twitch muscle fibers - muscle fibers that tire more quickly.
The researchers also observed signs of impaired energy production in the muscles. The mitochondria - often described as the cell’s powerhouses - functioned less effectively in patients with post-COVID and ME/CFS. In addition, fewer capillaries were found in the muscles of ME/CFS patients, 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 be simply explained by reduced physical activity or a loss of fitness. The muscles of these patients function differently in several ways compared to those of healthy people who have been inactive for a long time.
According to the researchers, this means that treatment and rehabilitation must be better tailored to the biological abnormalities found in these patients. Standard exercise programs based on typical deconditioning may not be appropriate for people with post-COVID or ME/CFS, especially when they experience post-exertional malaise: a worsening of symptoms following physical or mental exertion.
The study was conducted by researchers from Vrije Universiteit Amsterdam and Amsterdam UMC, in collaboration with international partners. The research was made possible in part by ZonMw, Solve ME, the Long COVID Foundation, ME Research UK, and the Patient-Led Research Collaborative, among others. The study contributes to the ZonMw-funded Post-COVID Network Netherlands (PCNN).
