Over the last few years, I have tried excersing every few months. Most of time, I'd workout too hard when starting, then I'd catch a cold, which would usually develope into a sinus problem. After I would recover, I'd lose all motivation to go at it again. Well, recently I started again, and started much easier this time. All was well until I started riding my bike hard. Sunday and Monday I went on 18 mile rides, pushing somewhat hard, and after Monday's hour ride, I worked out my upper body for about 45 minutes. Close to bed time the coughing started, and today I fell horrible, very weak, coughing, a bit light headed. Finally, my question, does over exerting yourself weaken the immune system? If so, what can be done to prevent this? Taking vitamins? Eating better? I'm guessing if my body is trying to heal my muscles, other "systems" in your body get neglected somewhat? Is this correct or do I have NO idea what I'm talking about? Thanks, Mike D.