Should You Workout When You’re Sick? Here’s How to Tell, According to Doctors

You wake up ready to hit the trail for your favorite weekday run, but when you get out of bed you don’t feel so well. You have a throbbing headache, a sore throat, and a runny nose. No fever, thankfully, but you’re definitely under the weather. What now?

Is it OK to workout when you’re sick—or is it better to take time off? In some cases, a good sweat might help make you feel better and give your body and immune system a boost—in other cases, rest is best, and exercise could make your cold or other illness worse.

“The traditional illness-related criteria for exercising are not evidence-based, but generally accepted,” says William O. Roberts, MD, MS, professor at the University of Minnesota Medical School. What you should do depends on how you feel sick.

When You Shouldn't Exercise if You're Sick

You have symptoms below the neck.

“The criteria I use to continue exercise with symptoms of illness are no fever, no symptoms below the neck, and no cough,” Dr. Roberts says. In other words, if you don’t feel well in your body (think: muscle aches, total body exhaustion), resting is a better choice than powering on with your workout.

"It’s probably never good to exercise when you’re ill with fever, diarrhea, or vomiting,” Dr. Roberts adds. These particular symptoms signal that your whole body (a situation known as systemic) is involved in the illness. They’re also symptoms of sickness that are dehydrating, and sweating during exercise could force you to lose more fluids when you should really be replenishing them. In these cases, rest instead of working out. 

You're possibly contagious.

Airborne viruses spread easily from person to person. If you determine you’re feeling bad because of a virus, like a cold or flu, stay home and take a break for the sake of others, especially if you’re an indoor gym exerciser.

Tips for Working Out When You're Sick

Get cleared to exercise by your doctor.

Always check with your doctor before exercising so you can figure out what’s causing your symptoms, advises Sarah Pace, ACE-certified personal trainer and corporate fitness regional manager at HealthFitness. You’ll want to know if it’s a common cold you caught from your neighbor or something more serious.

Choose light- to moderate-intensity movement.

If you’ve determined you’re not contagious or experiencing symptoms below the neck—and you feel up for it—you're probably OK for mild exercise. “It’s important to reduce your intensity and length of workout,” Pace says. You may want to treat the days when you’re sick like active recovery days. “Include some stretching or an easy walk instead of your usual routine,” if it’s more intense, she recommends.

Don't go all-out if you're lifting weights.

Planning on weight training? Remember that your body is already dealing with an illness, so a really intense lifting may add unnecessary load to your system. “When you’re pushing yourself in a workout, especially with weight training, you’re breaking down the muscle fibers and creating micro tears, which creates inflammation in the body,” says Nicole Simonin, personal trainer. This is important to remember because, “your body is now divided on taking care of your illness and your ‘injured’ muscles.” Lifting heavy weights may slow your recovery from illness (and also feel harder than usual).

Ease back into your routine.

Once you feel like your old self again, don’t push it too quickly. “In the bigger picture, skipping your workouts for a couple of days is not going to set you back significantly,” Simonin says. She recommends coming back to your exercise routine slowly and easily. “When you workout, you’re creating an inflammatory response in your body. Couple that with being sick, and you’re possibly [prolonging] your illness,” she adds.

Listen to your body's cues.

“If you’re performing lower-intensity exercise and start to feel crummy, take a break,” Pace says. Again, missing a few workouts won’t make or break your fitness goals. The most important thing is taking care of your overall health. Sometimes self-care means exercise, but when you’re super under the weather, self-care usually means rest.