Should You Exercise When You're Sick?

By Julie Vargo, Editorial Contributor

As a preemptive strike against illness, exercise gets a thumbs-up. But it’s lousy therapy once you are sick and downright dangerous if you have a fever-producing illness such as the flu.

“If you have a fever, definitely don’t try to sweat it out by exercising,” says Dr. Harrison Youmans, a sports medicine physician at Orlando Health. “Working out when your temperature is elevated, especially here in Florida, puts you at a higher risk for heat stroke and heat exhaustion.”

A body infected with the flu virus reacts differently to exercise, says Dr. Youmans. “If you over-exert yourself when you have the flu, you can make things worse very quickly.”

Exercising while you have the flu can cause the muscles in your airways to tighten more and quickly, creating an asthma-like condition that makes it difficult to breathe. Without proper rest and hydration, the flu also can evolve into bronchitis — or worse. An inflammation of the heart muscle, known as viral myocarditis, can occur when the body is over-exerted during a bout of flu. Ditto pneumonia.

“Getting the flu is frustrating for those who train intensely, like marathon runners and other competitive athletes, because it disrupts their workout schedule,” says Dr. Youmans, who also serves as a team physician for the Orlando City Soccer Club.

What About a Cold?

If you have a simple cold and feel up to it, you can continue to work out. But don’t expect your daily walk or yoga class to cure you. Research shows exercise has no effect on the duration or severity of run-of-the-mill respiratory viruses.

“Physical activity is great medicine for preventing all kinds of health problems,” says Dr. Youmans. “But once you’re sick, exercise doesn’t really help you get better.”

So how do you know when you can — or shouldn’t — work out? According to Dr. Youmans, if your symptoms are from the neck up — sore throat, stuffy nose, sinus congestion — pounding the pavement or pumping iron is fine. If symptoms are neck down and include body aches and a fever, bypass the gym and hit the couch instead. Once your fever breaks, it’s best to wait a few days before slowly restarting your exercise program.  

“Listen to your body,” says Dr. Youmans. “When it comes to exercise, respiratory viruses and the flu, patience may be the best medicine of all.”

Exercise As Prevention

If you are healthy and want to prevent the common cold and other respiratory infections, 30-45 minutes of moderate aerobic exercise daily can boost your immune system and cut your risk of illness by more than half.

“When you exercise, you increase the circulation of antioxidants through your body,” says Dr. Youmans. “Physical activity also helps with weight management, improves cardiovascular health and prevents some chronic illnesses. People who exercise also usually have better diets.”

But too much of a good thing can be, well, too much.  “Moderation is key,” says Dr. Youmans. “Very intense exercise can briefly depress the immune system. Elite athletes who train intensely actually have more respiratory illness, not less.”