Originally Posted by Carbonfiberboy

I was saying that about daily 100 mile rides. One of my riding buddies did 25,000 to 30,000 miles/year for a few years and that's how described how much he ate for dinner. It's different when you do that every day. One year he gave up on mileage goals and did gain instead. He did 1.5 million feet. He wasn't skinny but certainly not overweight. Just an average guy and a fast climber, though he obviously never rode what we would describe as "hard."

Originally Posted by Iride01

I over simplified the factors. If you look at the rate of fat being converted to energy while riding, it does go up, when you increase effort. But not much. You glycogen reserves get used up at an increasingly faster rate compared to energy from fat as you increase effort.

Once you deplete your glycogen your fat conversion to energy won't ever be able to give you as much energy as you need to keep you going at the same level. So you either slow down and rest or you bonk on the next hard climb.

Glycogen can be replaced from fat conversion if I remember correctly. But since on a ride you are using quite a bit of energy it's a slow process. But you want Glycogen. It's the energy source that will let you make that hard effort to sprint or out climb you previous record or others.

Glycogen is created faster in the body from carbohydrates. That's the reason many of us drink or eat carbs while riding. The faster absorbed the faster they are available for creating more glycogen to make that next best effort.

Unless every part of your diet is carb free, then the glycogen reserves in your body probably came from carbs more so than fat. The average fit person probably has 1-1/2 to 2 hours of glycogen in them. So until you exhaust your glycogen on a ride, then as you go from easy effort to hard effort, most of that increase in effort is fueled by glycogen, not fat.

Any how that's how I've always thought of it. But I admit this stuff is above my pay grade. So I've probably gotten some stuff wrong. So I won't mind much if someone needs to correct something.

I guess to be more correct I should have phrased it that as effort on a ride increases the amount of energy obtained from glycogen stores increases much faster than energy from fat stores.