"The threshold seems to be that the immune system stress response remains pretty good up to around 75 to 90 minutes of high intensity, unrelenting activity," Nieman said. "After that point, the muscles begin running low on fuel, stress hormone levels rise sharply and you begin to see every type of cell in the body mount a stress and dysfunction response."
But since most Americans aren't in danger of going overboard with their workouts, physical activity can be a cheap, easy defense against the common cold. And while it's true you can't stop what germs you encounter, Nieman said it's still a good idea to keep your hands clean.
Do any exercise aficionados out there care to share their experience with exercise to ward off illness? Or do you disagree with the whole connection between fitness and staying cold-free? Post your comments below.