I've heard this question phrases a few ways:
Should I exercise when I'm sick?
Should I exercise if I have a cold?
Should I exercise when I'm ill?
So I went to the Internet to find out. I found a few articles and here is what they said (as I summarize)
If you illness is “above the neck” (nose, etc) then you could exercise at a greatly reduced intensity.
If your illness is below the neck (chest, cough, etc), the NO you shouldn't.
Many articles also said to be VERY CAREFUL about this. Your body is already working overtime fighting the infection. If you come in now and want it to focus on building muscle, etc then you are distracting it (and in trying to do both – you may weaken your body – and thus give the illness an advantage).
The people who are really troubled that they may lose their routine of exercise is who should worry. Myself, I have a stuffed up nose. I have my exercise clothes sitting next to my Tony Little Gazzelle (my piece of equipment at home) and I know the minute I can exercise I will pick up where I left off.
Since I can't exercise, I should concentrate to make sure what I am eating is really healthy to make sure my body has the best fuel to fight the infection. Be careful. In my case I have NO appetite. While you may feel this is great and enjoy starving yourself without the will power, you body NEEDS fuel to keep going. Depriving your body will only weaken it and possibly lengthen the illness.
Remember rule #1 Live right. That means eating healthy. It will help you get back on the treadmill in no time.
Keep in mind. I am not a doctor, and before considering any exercise program you should consult your doctor – especially if you are ill.