Researchers at Vrije Universiteit Amsterdam and Vrije Universiteit Amsterdam (VU) have uncovered evidence explaining why individuals with long Covid endure prolonged fatigue, discomfort, and pain after physical activity. The study, published in Nature Communications, examined 25 long Covid patients and 21 individuals who had recovered fully from Covid.

The participants, all of whom were previously healthy and within working age, engaged in a short exercise on a bicycle. The results showed that, on average, those with long Covid had a reduced exercise capacity compared to healthy participants. The researchers looked at the blood and muscle tissue 1 week before the cycling test and 1 day after the test.

The researchers discovered that the persistent fatigue in patients with long-Covid has a biological cause, namely mitochondria in muscle cells that produce less energy than in healthy patients.

"We're seeing clear changes in the muscles in these patients," said Michèle van Vugt, Professor of Internal Medicine at Amsterdam UMC.

"We saw various abnormalities in the muscle tissue of the patients. At the cellular level, we saw that the mitochondria of the muscle, also known as the energy factories of the cell, function less well and that they produce less energy," said Rob Wüst, Assistant Professor at Department of Human Movement Sciences at the VU University.

"So, the cause of the fatigue is really biological. The brain needs energy to think. Muscles need energy to move.