Originally Posted by Carbonfiberboy

Well . . . the thing is that this fat burning business is an adaptation in response to endurance training, as is well documented in achoo's links. If one doesn't care about endurance performance and only wants to put out max effort for short periods like a track sprinter might, then endurance training would be contraindicated. This document:
http://www.ridethetrack.com/pdf/train_rodamaker.pdf
explains training differences for track events of differing lengths.

I thought Chapple went into why fat burning is important for roadies quite well: IIRC, in his experience it increased power output by having the rider utilize more energy pathways. That's one thing. In my own experience, fat burning is important because it spares glycogen. We have a limited amount of that, but we have a virtually unlimited supply of fat. So the higher the proportion of fat we can burn at a given power output, the faster we can go over a long time period because we can titrate our glycogen supply and make it last for the whole ride. Hence the dictum to spin faster on long distance rides, thus using more oxygen but sparing leg glycogen.

How far can it be stretched? Certainly for 24 hours. 24 hour TTs exist, and a fast rando rider can complete a 600k route in about that long without bonking. Then there's RAAM. I don't know how much glycogen can be replenished during their short 2 or so hour rest periods. I don't think it can be replenished during exercise, but I don't have a link for that. But RAAM racers obviously run mostly on fat and blood sugar.