How to know when it's safe—and when it's risky.

By Gabrielle Kassel
December 10, 2018

To avoid getting a cold or the flu, you take every precaution: You got a flu shot, you spritz hand sanitizer everywhere, and you keep your distance from coworkers with cold or flu symptoms. You even committed to the gym harder than Harry and Meghan Markle have committed to each other after learning that regular moderate exercise strengthens the immune system, one study review suggests.

But then, ugh, your get sick anyway. You're not totally incapacitated, and you hate the idea of undoing your fitness progress. So you wonder: Should you take rest days until you're symptom-free, or is it okay to hammer through your workout even though your nose is dripping and your body aches? The answer comes down to what your symptoms are—and how bad you actually feel.

RELATED: Is It too Late to Get the Flu Shot?

If you have a cold

If your symptoms are those typical of the common cold—a runny nose, sore throat, watery eyes, or the sniffles—and you don’t have a fever, it’s safe for you to proceed, Brian Babka, MD, sports medicine specialist and team doctor for Northern Illinois University athletics, tells Health. Basically, you want to follow what's called the neck rule: If all of your symptoms occur at or above your neck (with the exception of a fever), it's fine to sweat.

However, since you're probably not feeling 100% anyway, Dr. Babka suggests dialing back the intensity. You can still exercise, but this is not the time to do speed work, interval training, or one-rep maxes. “Intense exercise taxes the immune system, so if you overdo it, you’re ultimately slowing down your healing,” he advises. And of course, if your symptoms worsen while you're doing your workout, stop.

If you do decide to hit up the treadmill or go to kickboxing class, be careful about not transmitting your cold virus to other gym-goers. “If you’re coughing, sneezing, or even mouth breathing, you could be spreading your germs, especially if you’re not taking care to wipe down the machines and equipment after,” Honore Lansen, MD, an internist and family practitioner at One Medical in New York City, tells Health. For this reason, Dr. Lansen recommends sticking to an at-home or outdoor workout—weather permitting.

RELATED: 3 Ways to Tell the Difference Between the Flu and Pneumonia

If you have the flu

Back to the neck rule again: If you’re experiencing below-the-neck symptoms like chills, chest congestion, and body aches, or you have a fever, make it a rest day...or a rest week, actually. A fever, chills, and body aches are characteristic of the flu. Exercising with the flu can actually be dangerous because it can lead to dehydration and prolong your misery.

Swapping your sneakers for slippers may be a tough call for gym lovers, but Dr. Babka says it won't mess up your training. “A couple days off aren’t enough to de-condition your body," he asserts. "In all honesty, you could go up to two weeks before you start losing your engine or muscle mass.”

One more reason to stay at home: You risk transmitting the flu to everyone in the weight room. “The influenza virus is highly, highly contagious. If you go to the gym when you have the flu, you’re exposing other people to the virus,” says Dr. Babka. Wait until your fever has been gone for at least 48 hours, without the help of any meds, he says. Then, for your first few days back, stick with 30 minutes of low-intensity movement like walking or yoga.

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