It basically says there's this thing called the "neck rule".. if you're sick above the neck (head cold), you can exercise, but if you're sick below the neck (chest cold) avoid exercise. Of course they said if your head cold is severe, don't exercise too.
My own take on it is "anything with less than 38,5°C fever means I can at least go out for a walk". But in my case, that's more of a survival mechanism, because staying a whole day in a 20sqm one-room apartment drives me crazy even when I'm good health.
Of course, I don't mean strenuous exercise. Just walking and breathing some fresh is already a good thing. (My doc says the same thing, by the way.)
Unless I have a fever, I usually try to something (even if it's to go to the gym to just stretch). I usually I find that I can do more than I thought I could.
Exercising when you're sick
