Originally Posted by cyclezen

many riders, if they know a steep uphill is ahead, tend to slow down enough to get their heart rate down ... if you do that too early, the oxgenation of the blood falls also, and then the extreme of the pitch causes a major jump in heart rate - to load the blood with O2 again. But it doesn;t catch up quick enough to bring the blood O2 to the level needed, so you go anaerobic...