Carbohydrates are needed to fuel your muscles for exercise. An average 150 lb male has about 1800 Calories worth of carbohydrates stored in his body. 78% of that is in his muscles; 18% is in his liver; and 4% is in his blood. Carbohydrates in the muscles, stored as glycogen, are released during exercise. The glycogen stores in the liver are released into the bloodstream to maintain the blood glucose level, which feeds the brain.
The blood glucose levels must be maintained. Otherwise, you “hit the wall” or “bonk.” You feel overwhelmingly fatigued and yearn to quit. Before you exercise, you should load up on carbs to maximize your stored glycogen. In experiments, cyclists were able to ride more than twice as long when they were carbohydrate-loaded versus when they were glycogen-depleted.
Athletes are limited by carbohydrate, whereas non-athletes, doing light exercise, burn fat. During moderate exercise, 50-60% of the calories burned are from fat. When you exercise hard, however, you primarily use glycogen stores.
The good news is that, with training, your muscles increase their ability to store glycogen. A trained muscle can hold nearly three times the amount of glycogen as an untrained muscle.
If you are training for an event that lasts more than 90 minutes, then you should consider carbohydrate loading. This is not a one time event. You must carbohydrate load daily, especially in the days leading up to the event. Eat enough protein, but do not overdo the fat. As with your normal diet, continue to eat fiber rich foods. Don’t eat a large meal right before the event. It may be best to eat a large lunch on the day before an event, and then eat a smaller dinner and a small breakfast the next day. Don’t skip breakfast. It is a chance to give you one last intake of carbohydrate. And, this may sound obvious, but many don’t follow it. Don’t eat new types of foods in the days leading up to the event. You don’t know how your system will react to them. Focus on tried and true foods that you know won’t give you an upset stomach.
Meal replacement drinks, especially those high in protein, are a perfect source of nutrition and energy after your carbohydrate loading meal. The servings will be moderate, and choose one with a good mix of carbs and fats as well as protein. The protein will be critical for muscle repair as you head into your event.