Dr. Jack Gwaltney, a professor of internal medicine at the University of Virginia School of Medicine, has spent 40 years researching colds.
has yet to see solid evidence that exercise has anything to do with warding off colds.
It's exceedingly difficult to create a placebo-controlled, double-blind study -- the standard of medical research -- for such a study for one simple reason: People who exercise know they're exercising, while people who are told not to exercise know they're not, Gwaltney
This opens the possibility of biased results.
"I don't know of any convincing evidence that exercise prevents colds or helps you get over colds," Gwaltney
More than 200 viruses are known to cause the symptoms of a common cold.
Adults average from two to four colds a year, according to the National Institute of Allergy and Infectious Diseases
Symptoms of a cold usually begin 12 hours after infection and include nasal discharge, swelling of the sinus membranes, sneezing, sore throat, cough and headache, Gwaltney
The flu can interfere with blood oxygen levels, while head colds do not, Gwaltney