INDIANAPOLIS – As the weather turns colder, the U.S. launches itself full-force into cold and flu season. While recent research has correctly reported that exercise can help prevent the common cold, experts with the American College of Sports Medicine (ACSM) recommend caution for people who are considering an intense workout while they’re sick. In fact, there are some cases in which exercise could do more harm than good.

ACSM Fellow David C. Nieman, Dr.P.H., says that moderate exercise (30 minutes a day, on most, if not all, days of the week) actually lowers the risk for respiratory infections.  Prolonged, intense exercise, on the other hand, can weaken the immune system and allow viruses to gain a foothold and spread.

“The good news, for the majority of fitness enthusiasts who put in 30-60 minutes of exercise most days of the week, is that the number of sick days they’ll take during the common cold season is reduced by at least 40 percent,” said Dr. Nieman.

People who are already sick should approach exercise cautiously during their illness. To help people decide whether to hit the gym or stay in bed, Dr. Nieman offers the following recommendations:

• DO exercise moderately if your cold symptoms are confined to your head. If you’re dealing with a runny nose or sore throat, moderate exercise is permissible. Intense exercise can be resumed a few days after symptoms subside (in cases of the common cold).
• DON’T “sweat out” your illness. This is a potentially dangerous myth, and there is no data to support that exercise during an illness helps cure it.
• DO stay in bed if your illness is “systemic” – that is, spread beyond your head. Respiratory infections, fever, swollen glands and extreme aches and pains all indicate that you should rest up, not work out.
• DON’T jump back in too soon. If you’re recovering from a more serious bout of cold or flu, gradually ease back into exercise after at least two weeks of rest.

“In general, if your symptoms are from the neck up, go ahead and take a walk,” said Dr. Nieman. “But if you have a fever or general aches and pains, rest up and let your body get over the illness.”

Dr. Nieman also encourages people to engage in moderate-intensity exercise before getting a flu shot. After exercise, he said, the body responds better to the vaccine and gets a boost in immunity.

For more information, check out “Exercise and the Common Cold,” ACSM’s fact sheet dedicated to the relationship between safe exercise and illnesses. This fact sheet, written by Dr. Nieman, is part of a Current Comment fact sheet series available online.

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The American College of Sports Medicine is the largest sports medicine and exercise science organization in the world. More than 40,000 international, national and regional members and certified professionals are dedicated to advancing and integrating scientific research to provide educational and practical applications of exercise science and sports medicine.