Depending on your cold symptoms, running outside could be unhealthy.
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Knowing how tough it is to get back into a workout routine is what keeps a lot of people running in any type of whether, even if they aren't feeling well. When you have a cold, your body feels run down because it's using energy to fight off the virus. That doesn't necessarily mean that you shouldn't run when you have a cold, but running in the cold when you're ill is a different story.
The Neck Test
Use the neck test to determine whether you should run at all when you have a cold. If all your symptoms are above your neck, you should be OK to run, and running outside won't automatically make it worse. In fact, the Mayo Clinic says that exercise can even help alleviate cold symptoms by opening your nasal passages and easing nasal congestion. With symptoms below the neck, though, such as chest congestion and an aching body, you should pass on running, especially outside in the cold air, as it could aggravate your condition and even turn your cold into a more serious illness.
Never With a Fever
If you're not sure whether your symptoms are serious enough to keep you from running, your temperature will give you a clear indication. You shouldn't run if you have even a slight fever. A temperature of 99 degrees or more is high enough to keep you indoors and resting. Don't kid yourself about sweating the fever out with a brisk run through the chilly air. Running doesn't help combat a fever, and running in the cold will exaggerate the discomfort you're already feeling from the chills. Additionally, running with a fever is hard on your heart, as it will have to work overtime to keep your body's already elevated temperature down.
Running in the Cold With a Cold
Cold air is dry air and can cause your airways to constrict and irritate your nasal passages, making them particularly uncomfortable when they're already aggravated by a cold. Wearing a scarf over your nose and mouth will filter the cold, outdoor air you breathe to minimize discomfort and prevent it from damaging your airways. Ease up on your run just a little, too. Cut back on the intensity and don't run as far as you normally do. And remember to drink plenty of water -- 3 to 4 quarts per day, according to Stew Smith at Military.com. Taking these precautions will give your body a bit of a break and can keep your cold from getting worse.
Don't Make it Worse
Even if you determine that your cold isn't serious enough to keep you from your run, you still might want to choose alternatives to running outside in the cold. Running in a pool is a cross-training opportunity that provides resistance, and the atmosphere isn't as dry as the outdoors. You can also workout indoors, hitting the treadmill instead of a frosty outdoor trail. It's hard to give into your cold and not work out at all, but making small compromises can keep you running without risking your health.