Experts like to cite a rule of thumb known as the “neck rule.” If your symptoms are all located above your neck (stuffy nose, scratchy throat, headache), you almost certainly have a head cold and can hit the road or treadmill safely. If, on the other hand, you have a fever, congestion in your chest and lungs, or feel achy, it is probably a sign of flu, bronchitis, or another more serious ailment, and you should rest up. (Exercising with a fever will make you more vulnerable to dehydration, among other ill effects.)
Even if you pass the neck test and are determined to get a workout in, you should take it easy at first. “To be prudent, Id recommend cutting exercise duration and intensity when symptoms are present,” says Woods.
If you work out in a public gym, be extra vigilant when exercising with a cold. Germs can be transmitted through the air and through any person-to-person contact, so if you use a treadmill, gym mat, or barbells, be sure to be extra careful when it comes to wiping down the equipment. And avoid touching your face after handling equipment; you can pick up germs that will be more likely to infiltrate your body that way.