Any race longer than 15 miles is a fuel economy run. You have got to think, the whole way, about being as gentle on the pedal as possible. When talking about fuel supplies, I use the analogy of a fuel tank which is being supplied by a trickle of fuel from the mobilization of fat. There is some evidence that this fat mobilization does not really get going at its maximum level at the start, so this is another reason for starting at a level pace.
The Complete Distance Runner by Bruce Tulloh; Granada Publishing, 1983