After COVID-19, resuming regular exercise may be harder, and new research suggests this may be one more symptom of long COVID.
For the study, the researchers reviewed 38 published studies that tracked the exercise performance of more than 2,000 people who had had COVID-19. Ultimately, the investigators zeroed in on nine studies that compared performance of 359 participants who had recovered from the virus to 464 who had long COVID symptoms.
More than three months after having COVID-19, their capacity for exercise was like that expected from someone 10 years older. While not a proven symptom of long COVID, loss of exercise capacity seems to be a consequence of the disease for some, the researchers said.
"Reduced exercise capacity is one potential symptom of long COVID," said lead author Dr. Matthew Durstenfeld, an assistant professor of medicine at the University of California, San Francisco. "Further research is needed to understand the trajectory of exercise capacity after COVID-19 and identify treatments for long COVID."
And, he added, the lower capacity for people with long COVID lasts at least three months after infection.
The studies reviewed relied on data from cardiopulmonary exercise testing. Participants' oxygen and carbon dioxide levels were measured while they used a treadmill or stationary bike. Other signs of heart and lung function were also measured.
The findings suggest that people with long COVID may suffer from irregular breathing patterns, reduced oxygen extraction in the muscles, and a greater inability to increase heart rate during exercise, the study authors said.
The tests also showed evidence of deconditioning, the weakness that occurs after most illnesses that result in inactivity. But deconditioning couldn't account for all of the loss in exercise capacity, the researchers noted.
For folks with long COVID, some activities may be too strenuous, Durstenfeld said. He cited doubles tennis and lap swimming as examples.
Impaired oxygen use might reduce the exercise capacity of a 40-year-old with long COVID to that of someone 10 years older, he added.
Not everyone with long COVID will have a lower capacity to exercise, however, Durstenfeld noted. Some may have severely decreased capacity; other may experience no decline.
"Some people can't exercise as much after COVID as they could before, especially those with other symptoms of long COVID," he said. "Cardiopulmonary exercise testing may help identify reasons for exercise limitations."
Dr. Benjamin Hirsh, director of preventive cardiology at the Sandra Atlas Bass Heart Hospital in Manhasset, N.Y., reviewed the study findings.
"Finally, we see a compendium of convincing evidence that patients with long COVID can have significantly reduced capacity to exercise or even walk upstairs," he said.
Hirsh noted, however, that the researchers couldn't tell if patients who were older or obese suffered more than younger, thinner patients. He pointed out that most patients with long COVID were not hospitalized, "so people should be informed that this can affect any patient who has had COVID."
Hirsh offered a theory about the physical changes identified in the study.
"COVID can cause alterations to metabolism, the way oxygen is exchanged and delivered to tissues and effects on the nervous system, which may account for the effects the researchers found," he said. "We now need to look towards interventional rehabilitation strategies to address the symptoms."
The findings were published online Oct. 12 in JAMA Network Open.
To learn more about long COVID, visit the U.S. Centers for Disease Control and Prevention.
SOURCES: Matthew Durstenfeld, MD, MAS, assistant professor, medicine, University of California, San Francisco; Benjamin Hirsh, MD, director, preventive cardiology, Sandra Atlas Bass Heart Hospital, Manhasset, N.Y.; JAMA Network Open, Oct. 12, 2022, online