WEDNESDAY, May 31, 2023 -- Lack of energy for exercise is a common problem for folks with so-called long COVID.
New research pinpoints the most likely reason why: diminished capacity to get the heart pumping fast enough to support the effort. The name for this is chronotropic incompetence.
“The amount of aerobic exercise an individual can do is limited largely by the delivery of oxygen by the heart, lungs, blood, and its use by the muscles,” noted study first author Dr. Matthew Durstenfeld, a cardiologist and assistant professor of medicine at the University of California, San Francisco.
“If the heart can't pump as fast, you can't exercise as much," Durstenfeld said.
Chronotropic incompetence wasn't the only reason people with long COVID had lower than expected exercise capacity in the new study, “but it was surprisingly common among people with long COVID,” he added.
Some people infected with COVID-19 can develop a wide range of ongoing health problems. These conditions can last weeks, months or years, and have been labeled long COVID.
Using biomarker testing, the researchers found inflammatory biomarkers early on in long COVID patients.
They also discovered that all patients who struggled with a reduced capacity to exercise also experienced reactivation of a prior infection with the Epstein-Barr virus (EBV). Epstein-Barr is linked to mononucleosis and multiple sclerosis.
“EBV reactivation is common after SARS-CoV-2 infection in general,” Durstenfeld noted, “so it is hard to tell if this is a chance finding or a meaningful clue from our study.”
For this study, researchers looked at 60 adults who had had COVID-19 and assessed them about 18 months after their initial infection. Average age was 53. Participants underwent MRI scans and aerobic exercise tests, alongside heart rhythm monitoring, while on stationary bikes. Blood samples were also taken.
The exercise tests revealed that nearly half with symptoms suffered from a markedly reduced exercise capacity, versus 16% without symptoms.
The findings suggest that chronotropic incompetence -- failure to achieve 80% of expected maximum heart rate while exercising -- contributes to exercise limitations in long COVID, said Durstenfeld.
The average capacity drop was roughly equivalent to 10 years. “A 40-year-old woman can only exercise as much as a 50-year-old woman,” Durstenfeld noted.
Put another way, the same person who pre-COVID could have played doubles tennis would now only be able to handle golfing with a cart, he explained.
So what does explain the link between long COVID and chronotropic incompetence?
Durstenfeld said there’s no clear answer yet, though he suggested that “it may have something to do with inflammation or the autonomic nervous system.”
For now, long COVID patients who find it difficult to exercise -- particularly those with severe long COVID -- may need to pace their activity with guidance from a rehabilitation expert, if possible, Durstenfeld said.
“My hope is that treatments are discovered for long COVID that they will help people recover their lost exercise capacity,” Durstenfeld noted. “But we still do not have any proven treatments.”
Dr. Leslie Rydberg is an attending physician at Shirley Ryan AbilityLab in Chicago.
Rydberg, who was not part of the study, suggested that “the best way to help people with long COVID increase their ability to be active is to figure out which activities or exercises they can do without exacerbating their symptoms, and build that into their daily routine.
“Then they can very slowly and gradually increase the amount of time they do that activity,” she added, while cautioning that patients should decrease activity levels if and when symptoms increase.
The findings were published recently in the Journal of Infectious Diseases.
The U.S. Centers for Disease Control and Prevention has more on long COVID.
SOURCES: Matthew Durstenfeld, MD, MAS, assistant professor, medicine, University of California, San Francisco, and cardiologist and physician-scientist clinical researcher, Zuckerberg San Francisco General Hospital; Leslie Rydberg, MD, attending physician, Shirley Ryan AbilityLab, Chicago; Journal of Infectious Diseases, May 11, 2023