Benjamin I. Rapport's study Metabolic Factors Limiting Performance Marathon Runners
This piece is getting some air time so I downloaded it. Its about marathoners but it could also apply to those who ride or run. Dr. Ben is an M.D. who runs marathons and also one with a computer science background. This makes his report unique.
I'm somewhat skeptical of this calculator, though... unless I put in an elite-level finishing time, it's telling me I don't need to consume any calories during the event. Hmmmm...
The calculator's estimate for the VO2Max might be part of the issue... my running VO2Max is only about average, but my resting heart rate is pretty low, and that seems to be a key variable for this calculator's VO2Max estimate.
I think his starting point is the amount of glycogen in your liver and muscles before you start the race. Of course, if you really want to push it, your storage needs to get replenished. I listened the last part in the car radio, a MIT student 100 lbs, 65 resting heart rate, can run 2 hours, 44 minutes, if she had enough glycogen in her system at the start. He said 1,900 of carbs (calories from carbs??) the night before the race.
If we take even a portion of a GU at the 10 mile mark and the 15, 20, maybe you'll have fresh legs again. That way the store of glycogen won't ever get near empty.