Is it OK to do? I remember one time I lifted intensely while I had a cold and it made me even sicker. I think someone said once that it is unwise to break down your muscles while sick because you need your immune system to fight the sickness instead of rebuild muscles. Is it OK to do cardio? I'm not terribly sick, just have a stuffy nose and sore throat in the morning. Been going on for a day or two and it sucks sitting at home knowing that I could be getting stronger or exercising my heart.