Sports drinks can do more than simply fuel your long runs and races.

Recently I saw a friend who was battling a bronchial infection. This friend is a runner, and like most runners he does not like to miss workouts because of illness. He was already dressed and ready to run when I saw him, and he asked me whether he should go ahead and do the workout or can it.

“That depends on two things,” I said. “If you honestly feel up to it and you can hold yourself back to a moderate effort, running will probably help you get better sooner. But if you feel lousy and you run anyway, or you run too hard, running will only make you sicker.”

I wasn’t just making this answer up. It’s based on solid research. For example, a 2009 study by researchers at the University of Iowa found that moderate daily exercise improved flu symptoms in mice infected with a flu virus. The key word here is “moderate.” Attempt only short, low-intensity workouts when you are experiencing cold or flu symptoms, stop exercising immediately if you feel horrible while working out at a low intensity, and simply avoid exercise completely if you feel miserable even thinking about working out. In short, listen to your body and use common sense when approaching training when you’re under the weather.

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Exercise is truly a double-edged sword in relation to cold and flu. Light and moderate cardiovascular exercise give the immune system a boost. However, strenuous workouts are known to result in an acute suppression of immune system function that can last for two to 72 hours afterwards, depending on the individual and the precise nature of the workout.

The primary cause of this suppression is the hormone cortisol. Cortisol is released by the adrenal glands in response to all forms of stress. Its main function is to stimulate the breakdown of proteins and fats in the body and increase the blood glucose concentration. Cortisol release is greatest during high-intensity exercise and in the latter portion of long workouts, when the preferred energy source of muscle glycogen has been depleted. As a side effect, cortisol suppresses immune system function by decreasing production of lymphocytes and antibodies, which are the warriors of your body’s immune defense.

In addition to the advice to listen to his body and take it easy, there was a second suggestion I gave to my runner friend with the bronchial infection: “Take a sports drink with you.”

Believe it or not, by drinking a good sports drink before and during workouts, athletes can minimize the immune suppression that comes with hard training. Research by David Nieman at Appalachian State University has demonstrated that the carbohydrate in sports drinks can combat the effects of cortisol on two levels. First of all, by taking in carbohydrate during workouts, runners are able maintain higher levels of blood glucose, which slows the use of muscle glycogen and delays the need for the use of protein as an energy source.

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In addition, carbohydrate stimulates the release of insulin from the pancreas. Insulin is a hormone that is responsible for delivering carbohydrate, in the form of glucose, to the working muscles. But it so happens that insulin also neutralizes cortisol and thereby reduces its effect on the immune system.

Of course my friend went ahead and ran. When I saw him afterward he said that he was mindful of his intensity and held himself back from running as hard as he would have done otherwise. I’m hopeful that his restraint and the carbs he took in while he ran will help him return to full health and normal training sooner. The next time you feel a tickle in your throat, be sure to do the same.


About The Author:

Matt Fitzgerald is the author of numerous books, including Racing Weight: How To Get Lean For Peak Performance (VeloPress, 2012). He is also a Training Intelligence Specialist for PEAR Sports. To learn more about Matt visit