Carb-loading is a popular pre-race ritual for many marathon runners.?

Someone once used this analogy and I have remembered it ever since:

Think of your body as a "hybrid" car. Where the fuel is both gas and electric. The electric portion are fats, and the gas portion are carbohydrates. Basically, the faster you go, the more gas you use (or carbs you use). In marathon preparation, usually people work on their bodies ability to use fats as a fuel resource, because if you don't run that often your body is REALLY bad at using it. Also, fat is for slow paces; ones where you don't go over your aerobic threshold, i.e. starting to building lactic acid.

1. Carbo loading before a marathon basically makes sure your body has adequate "gas" for the race. Knowing fully that you WILL eventually run out of gas towards the end of the race.

2. Not really knowledgeable on the ATP system as it's "immediate" fuel for things like sprinting. I wouldn't worry about this very much for marathon. It's more of a weightlifting/sprinting deal.

Hope this helps!

Wow, your question is pretty advanced.

I doubt i understand this stuff at the level you want but I am pretty sure i can give you a decent answer to part one.

So the muscle cells use glycogen as fuel. And the muscles store some glycogen but that amount is quickly used up (i'm sorry i don't know the time it takes). After that the muscles start grabbing glucose as it passes by in the bloodstream. As the glucose level falls, the insulin levels rise, and the liver starts releasing its stored glycogen into the blood stream.

Now, the liver does store fat just to convert into glycogen when necessary, but either it takes too long or the rate of conversion is too slow for a marathon runner to finish the race on stored fat to glycogen.

but the carbs that the runner ate for dinner the night before haven't finished being converted into fat so the liver can turn those into glycogen faster.

Anyway, i don't know the times, and i probably got some of the stuff wrong. I'll check back later and see if anyone has improved on this.