Exercise after COVID-19? Take it slow.

COVID-19 has changed my advice.

Early in the pandemic, as the initial wave of patients with COVID-19 began to recover and clinically improve, my colleagues and I noticed that some of our patients were struggling to return to their previous activity levels. Some cited extreme fatigue and breathing difficulties, while others felt as if they just could not get back to their normal fitness output. We also began to hear of a higher than normal incidence of cardiac arrhythmias from myocarditis, inflammation of the heart muscle that can weaken the heart and, in rare cases, cause sudden cardiac arrest. Other complications like blood clots were also cropping up.

What was surprising is that we saw these problems in previously healthy and fit patients who had only mild illness and never required hospitalization for COVID-19.

In my sports medicine practice, a cyclist in her 40s with recent COVID-19 symptoms had leg pain that was abnormal enough to warrant an ultrasound, which showed near complete cessation of blood flow because of arterial and venous blood clots in both legs. Thankfully, our team caught these early enough that they did not spread to her lungs, which ultimately could have killed her. Recently, a college student in Indiana with COVID-19 died from a blood clot that traveled to her lungs. As the pandemic has evolved, we have learned of a much higher risk of blood clots from people who contract the virus.

In those early months of the pandemic, my colleagues and I learned of a New York City mental health worker in her early 30s, a dedicated athlete with no underlying health problems, who developed symptoms of COVID-19. Her low-grade fever and congestion went away, but she continued to feel “sluggish.” As she had done many other times after getting over an illness, she went for a run to feel better. She died on the run, of cardiac arrest; it appears she had undiagnosed myocarditis caused by COVID-19.

We now know the heart is a particular cause for concern after coronavirus infection. A study in JAMA Cardiology looked at 100 men and women in Germany, average age 49, who had recovered from COVID-19 and found signs of myocarditis in 78%. Most had been healthy, with no preexisting medical conditions. A smaller study of college athletes who had recovered from COVID-19 found that 15% had signs of heart inflammation.

As the pandemic continues, we have heard countless stories of elite athletes in top physical condition struggling to regain their form after COVID-19. More than a dozen women on the U.S. Olympic rowing team who contracted the virus in March described persistent fatigue for weeks after the initial illness. Recreational athletes, including runners and triathletes, have complained of prolonged respiratory symptoms during exercise. Pulmonary issues from COVID-19, including pneumonia, have caused breathing difficulty during exercise for weeks or months following infection.

To help patients safely return to activity after mild to moderate COVID-19 infection, my colleagues at Hospital for Special Surgery and I published an evidence-based set of guidelines based on the existing medical literature and our evolving understanding of the disease. Our “return to activity” guidelines urge far more caution than in the past, based on the unpredictable nature of how the virus affects each person.

Anyone who had severe illness or was hospitalized with COVID-19 needs to consult a physician about whether it is safe to exercise. But even people who experienced mild illness or no symptoms need to take precautions before exercising again. Among our new recommendations:

Do not exercise if you are still sick. Do not exercise if you have active symptoms, including a fever, cough, chest pain, shortness of breath at rest or palpitations.

Slowly return to exercise. Even if you had only mild symptoms, with no chest pain or shortness of breath, you should still wait until you have at least seven days with no symptoms before returning to exercise. Start at just 50% of normal intensity. A gradual, step-by-step and slow return to full activity is recommended.

Stop exercise if symptoms return. If you develop symptoms after exercising, including chest pain, fever, palpitations or shortness of breath, see a doctor.

See a cardiologist before exercising. If you experienced chest pain, shortness of breath or fatigue during your illness, you should see a cardiologist before restarting sports activity. Depending on how you feel, your doctor may conduct a test for myocardial inflammation.

Get tested. If you have cold or flu symptoms, get tested for COVID-19 before you return to exercise. If you think you might have had COVID-19, a test might help you and your doctor make decisions about safely returning to exercise.

And remember, as doctors we can run tests, but you know your own body better than anyone else. You know how you normally feel when you walk up the stairs, when you run, when you bike. If you have had COVID-19, are those things harder for you? Are you noticing a change in your body? If the answer is “yes,” it is important to speak with your doctor.

Even if you have never been diagnosed with COVID-19, be mindful of how you are feeling. Many people with COVID-19 do not know they have it, or have general symptoms like gastrointestinal upset, fatigue or muscle aches. So if you have been feeling “off” during exercise, listen to your body, ease up and check with your doctor.

COVID-19, an aggressive virus, spreads easily and carries significant morbidity and mortality. Cardiac risk in particular is greater with COVID-19 than with other viral diseases, so it makes sense to use caution.