Originally Posted by
R. D.
On a different note, remember that if you go above zone 2, it takes 20-30 minutes for your metabolism to come back to fat burning, so even detailed HR/power stats won't tell the whole story...
That's not true. The body burns fat during all exercise and even just sitting in your chair. It just can't burn it fast enough above a certain level of effort. So the energy needed is supplemented by glycogen and serum glucose.