Exercising & Colds*Exercising to the point of exhaustion can weaken your body's immunity. Elite athletes often complain of constant head colds.
*Exercising vigorously, but not exhaustively, at least every other day has the opposite effect -- it strengthens the immune system around the clock.
*Exercising moderately (e.g., walking) most days of the week appears to strengthen the immune system for at least several hours.
Bottom line: Every time you go for a brisk walk, your immune systems gets a lift that should increase your chances of fighting off a cold. This means your body theoretically destroys viruses you come into contact with before they have a chance to multiply and make you sick.
Source: David Nieman, DrPH, Appalachian State University, NC