According to WebMD Emilie was right. Moderately working out while you have a cold is not harmful to you or your health, in fact it may actually help the recovery from a cold. What you need to be careful of are the medications you are taking while you have a cold and the possible side effects; decongestant medicines increase your heart rate, consequently physical activity does the same. You should be careful, therefore, if you're using a decongestant and exercising that you are listening to your body. If you begin to feel lightheaded take a break and let your heart rate slow down. Also if you have asthma consult with your doctor regarding exercising with a cold. I have asthma and haven't had any problems with this but as with most medical conditions everyone's situation is different.
This past winter my colds and flu symptoms were little to none except for the times when I had taken a break from regular exercise. Now I'm not a scientist and I did not conduct any kind of experiment with control groups or that fancy smancy stuff but it's is a great coincidence that the weeks that I took multiple days off from working out were the times when I got sick.
A New York Times article written by Gina Kolata in 2008 talks about the findings of a study that asked this same question - Can you exercise while having a cold. To read the full details of the study you can view the original article here, but for the condensed version here's what was discovered - unless it's in your chest you can and should continue exercising. While it may not decrease the recovery rate you will feel better during the duration of the cold.
|Photo courtesy of Dan Pearce, Single Dad Laughing|