Prevent Bonking

Have you ever hit the wall? Ever bonked? If you did, it probably came right around the two hour mark. Do you know why? It's all about blood sugar. Your brain needs sugar to function, but it has no storage facilities. So all of the sugar that your brain needs must be delivered from your blood. This means, that for your body to be in proper operation, there must be a certain amount of sugar in the bloodstream at all times.
Most of the time, this is easy. (But not uncomplicated.) You eat, and your blood sugar increases. Insulin is released which opens up the cell walls of your fat and muscle cells, allowing for the intake of glucose and nutrients. Your body also has stores of glycogen (its molecule of choice for storing carbohydrate) to keep a constant supply of sugar in the blood. Your muscles contain 78% of the 1800 Calories. This is so that your muscles have a ready supply of fuel at all times. 18% of the glycogen is stored in the liver. This is where the glycogen comes from to regulate blood sugar. And 4% is in the blood. This is the stream that is needed to supply the blood.
When you exercise really hard, the glycogen stores in your muscles are reduced. When they are depleted is when you feel an immediate loss of energy and a desire to quit. You have just hit the wall.
You can prevent hitting the wall by eating carbohydrate before and during your exercise. Carbohydrates can be reduced in the muscles gradually over days of not eating enough. Thus, you should carbohydrate load daily, especially in the days before a big event. And while you are exercising, you should consume carbohydrate every two hours to keep your blood sugar levels in check.