The general rule is that steady, moderate-heavy exercise (walking, biking, jogging) drives it down, but like everything else in D-land there are exceptions. Lots of people report that short intense bursts of exercise--like sprinting, racing--seem to have the opposite effect, which seems to have to do with your adrenal system kicking in. My primary form of exercise is biking, and my experience is that it lowers my BG, except... I found last winter that as the weather got colder, past a certain threshold--as temps dropped into the 20s F or below--iit was having the opposite effect. I was shocked to find I'd get back from a 1/2 hr hard ride and my BG was actually UP by 40-50 points, once as much as 70. I think the colder temps convinced my body something else was going on--if I"m exerting myself so hard in this weather it can't be just recreational, I must be getting chased by wolves or a polar bear or something.