[QUOTE=hamster;16670793]Actually a good way to extend endurance is to do the exact opposite. Ride without any calories as much as possible. No sports drink, no PBJ, no peanut butter cookies unless you absolutely have to.
You have a certain amount of energy (glycogen) stored in the quads. When you ride, you burn some combination of muscle glycogen, fat and on-the-bike carbs. If you're just starting after a long break, your stores are low and you end up running out quickly. Long glycogen-depleting rides without calories encourage your muscles to store more glycogen and to use more fat. It is totally possible to go 60 miles at a brisk pace without any food (though maybe not in time-trial mode).
This is bad advice but a very common misconception. All this will do is slow you down and can make you sick.
It was known as bonk training. The theroy was that you would store more Glycogen and be stronger. but it will do the opposite.
No time for details now maybe later.