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A discovery in the muscles of long COVID patients may explain exercise troubles

SCOTT SIMON, HOST:

You know that feeling of muscle soreness a day or so after you've done a tough workout? Now imagine that but much more. That's what some people with long COVID face after they exercise. And as NPR's Will Stone reports, new research is giving scientists a clearer picture of what may be going on.

WILL STONE, BYLINE: Hit the gym. Get back in shape. It's advice many patients with long COVID have heard. David Putrino says this notion that exercise is medicine has proven difficult to dispel in the broader medical community.

DAVID PUTRINO: It is very clear that this is not a typical response to exercise. They feel incredibly unwell. They become bedbound. Their whole system feels as though they've been poisoned.

STONE: Putrino runs a long COVID clinic at Mount Sinai in New York, where he sees what's known as post-exertional malaise. It's a hallmark of long COVID and similar complex illnesses, like chronic fatigue syndrome. Symptoms are typically extreme muscle pain, fatigue and brain fog that last days, even a week after physical activity. But when they complain, Putrino says, so often patients aren't taken seriously.

PUTRINO: Their lived experience is not being listened to or validated.

STONE: That's why he says new research from the Netherlands is important because it shows clear evidence of a biological basis for their symptoms. Scientists there compared 25 people with long COVID to those who'd had COVID and fully recovered. Both groups did an exercise test on a stationary bike that lasted about 10 to 15 minutes. The research team drew blood and took muscle biopsies from their legs before and after the exercise. Braeden Charlton is at Vrije University in Amsterdam and one of the study's authors.

BRAEDEN CHARLTON: This is a very real disease, and we see this at basically every parameter that we measure.

STONE: After exercising, the consequences to the muscle were dramatic. Charlton says multiple tests revealed the mitochondria, the body's cellular power plants, are compromised, meaning their capacity to take up oxygen and produce energy is impaired.

CHARLTON: What we saw immediately, and it's very profound, is that their mitochondria don't function in a healthy way.

STONE: Charlton says they also found atrophy and immense amounts of cell death in the muscle tissue.

CHARLTON: There is a lot more muscle breakdown than we would expect to happen following the exercise.

STONE: Taken together, the results show widespread abnormalities that help explain patients' severe reaction to physical activity.

AKIKO IWASAKI: I think it's a very strong study, and the messages are striking.

STONE: That's Akiko Iwasaki, a scientist at Yale University who's studying long COVID.

IWASAKI: There's a real problem in converting oxygen into energy in these people, and literally, they can't recharge their battery.

STONE: The deep dive into muscles also turned up tiny blood clots. They were elevated in those with symptoms, and that only got worse with exercise. The clots were found inside the muscle, not in the blood vessels. That was a surprise to Resia Pretorius at Stellenbosch University in South Africa.

RESIA PRETORIUS: That means that the micro-clots can actually have traveled through the damaged vasculature into the muscle. And that is huge because if it can happen to muscle, then it can happen to the brain and any other organ.

STONE: And if the linings of the blood vessels are really that compromised, she says it would also cause problems with the mitochondria. More work needs to be done on these different lines of evidence. In the meantime, David Putrino at Mount Sinai says doctors need to take these findings very seriously.

PUTRINO: We need to step out of this erroneous mindset of, well, no pain, no gain. No, post-exertional malaise is different.

STONE: He says maybe with this new evidence, more people will listen.

Will Stone, NPR News. Transcript provided by NPR, Copyright NPR.

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Will Stone