A simple cold goes away sooner if you walk it off.

RODALE NEWS, EMMAUS, PA—Winter is a great time to get out and exercise, despite the fact that most people assume that it's a great time to come down with a cold or the flu. "People are very confused as to whether or not cold temperatures will cause them to get sick," says David C. Nieman, DrPH, FACSM, professor of health and exercise science and director of the Human Performance Lab at Appalachian State University. But it's the fact that people congregate indoors where viruses easily spread—not the cold weather itself—that makes these illnesses more prevalent during the colder months, he says. And knowing when to exercise and when to take it easy can lower your risk of getting sick, or even help you get better sooner.

THE DETAILS: It's fairly well known that exercise can boost immunity. However, Nieman just completed a study finding that it can reduce the severity of cold symptoms, as well. His 1,000-person community trial found that people who were physically active, were lean, and ate a lot of fruit experienced one-third fewer sick days than people who had lower physical activity levels and were overweight. And, he says, "When the active people got sick, their symptoms were less severe," he says. Previous research by Nieman has found that people who engage in moderate-intensity exercises like walking while they're sick can cut their sick times by as much as half if they exercise for at least 45 minutes five to six days a week.