Originally Posted by
waterrockets
If you're diabetic, that's one thing, but your muscles have enough glycogen in them from your previous meals. If you put anything substantial in your stomach, it gets the blood priority over your legs. Your legs will feel dead.
It's not about muscle glycogen; it's about liver glycogen and blood sugar. Both of these drop substantially overnight and can affect how you feel during your workout. You're right that eating a heavy meal before a hard workout is not a good idea, but a light, carb-only snack could help. Something like juice or gatorade. Also, unless you want to taste it continuously throughout your ride, don't eat anything with a lot of fat or protein less than a few hours before your ride.