It's rather logical in fact. When you exercise you damage your body, keeping your repair mechanisms active. However overexercise typically does more damage in

It's rather logical in fact. When you exercise you damage your body, keeping your repair mechanisms active. However overexercise typically does more damage in a session than your body can heal before your next session. It's rather safe to assume that when you contract a virus that when the immunological warfare is going on (our bodies first response is rather brutal and untargeted, the sore throat from a flu isn't from the flu, it's from your own immune cells killing - IIRC - roughly 20 healthy throat cells for 1 infected cell) and damaging our body that the repair mechanisms are coping with all too much. Not exercising doesn't put stress on our healing mechanisms, however it doesn't keep them active and trained (so to speak). Put it this way, the Police would take considerably longer to get to your house from the station than from one of their patrol routes; essentially the same is for our healing mechanism. Even if exercise doesn't have an effect on our immune system, I'm sure it will certainly increase recovery time (assuming you're not on the treadmill when sick) by decreasing healing time, which is ostensibly the factor that kills you and not the virus itself (assuming you haven't contracted the 1918 Spanish flu). I've only ever had one noticeable case of the flu (which happened when I moved country, so I'm unsure if it was a strain I'd never experience, similar to the current H1N1 'pandemic'), which I believe is due to frequent exercise (a job involving heavy lifting ~90lbs and constant weight carrying ~10 lb tool pouch and ~10lb hammer drill).