Should I work out when I’m sick?

Depends on the intensity.

feeling sick

Feeling sick

Someone is not in the mood to go to the gym.Depositphotos

You know it the moment you wake up: Last night’s little throat tickle has turned into a full-blown sneezy, nose-dripping, red-eye cold. You had plans to work out today, but would keeping them make your illness worse? In other words, should you stick with your exercise routine or indulge in some rest? Here are a few guidelines to help you decide.

Follow the "above the neck" rule

Exercising while you’re sick will not necessarily hurt your immune system. In fact, if you work out regularly, then you’ve almost certainly done so while your body was fighting off an illness.

"Up to half of rhinovirus infections are asymptomatic, so you never feel sick," says Bruce Barrett, a professor at the University of Wisconsin School of Medicine and Public Health. Similarly, 10 or 20 percent of influenza infections won't have any symptoms. It's very likely that you've hit the gym while sick, and you didn't even know it. So just because you can work out...should you?

Even that issue defies an easy yes-or-no solution. "Nobody has really done the type of study that would be required to answer that question definitively," says Bruce Barrett, a professor at the University of Wisconsin School of Medicine and Public Health. Still, doctors have a pretty consistent set of recommendations.

Michael Gleeson, a professor of exercise biochemistry in Loughborough University’s School of Sport, Exercise and Health Sciences lays it out: “The general rule is that it is okay to train moderately if your symptoms are above the neck—that is, a runny nose or sore throat. But if you have symptoms below the neck, such as coughing, a tight chest, or joint aches and pains, it is best to avoid all but the lightest exercise until at least two days after your symptoms have improved.”

And you should never exercise when you have a high fever, Gleeson says, so check your temperature before you hit the treadmill. If it’s 102°F or higher, stay home.

When you're sick, lower the intensity

So if you're just dealing with a little nasal congestion, you can exercise—but you should still ease off the fervor. We don't know exactly how exercise during a cold can affect you, but studies from Gleeson and other researchers suggest that intense exercise when healthy can increase your risk of getting sick. "People seem to have a higher rate of getting sick from a viral respiratory illness after a major physiological stress, including long-distance running or other long-distance aerobic exercise," says Barrett. "There's something about overworking the body that can dampen the immune system and increase the chance of getting a bug." Researchers are still testing this theory, but it means you should scale back on the intensity of your workout when you're sick.

While you struggle with an illness, your immune system releases cytokines, small proteins that regulate its response to an infection—but also make you feel tired and lethargic. During this time, Gleeson says, “Training will generally feel harder and fatigue will begin earlier. So stick to light to moderate training and avoid the high-intensity workouts. Moderate aerobic or strength training is okay, but do less than normal."

When you're healthy, exercise regularly

Even though intense workouts can increase your risk of illness, that doesn't mean you should abandon your exercise routine once you feel better. Both doctors stressed that working out can help stave off the next summer cold heading your way. "People who exercise regularly have fewer cold and flu infections, and research suggests that they have shorter and less severe episodes than those who don't," says Barrett. "So exercise is good." In addition to physical health, Barrett's work has also found that good mental and social health correlate with a lower risk of respiratory infections.

Barrett recommends everyone aim to spend at least 150 minutes per week doing moderate, sustained exercise. But it’s easy to let an illness derail your entire regimen. Will keeping up the consistency—even at a lower intensity—while you’re sick help you maintain your routine after you recover? If so, that’s a great reason to keep working out.