The easiest and one the most proven ways of improving performance is by manipulating carbohydrate intake, particularly for endurance type athletes or those involved in sports like soccer, water polo, and basketball.

Carbohydrates are simple sugars or long chains of sugars which are linked together [starches]. Paradoxically, carbohydrates are the preferred fuel during exercise of high intensity but they are stored in extremely limited amounts in the body. This storage form of carbohydrate, called glycogen, is found primarily in muscles and liver. The glycogen in the muscle is used directly by the muscle which is being exercised. In other words, once its limited stores of glycogen are gone it cannot "borrow" from other resting muscles.
Depletion of glycogen by the working muscles leads to severely impaired exercise performance, which at its extreme is known as "hitting the wall". This makes obvious the need to

1. increase glycogen stores prior to exercise, and
2. supply carbohydrate during prolonged exercise.

How much carbohydrate is enough? We often express recommendations in terms of percentages of total calories. Even recreational athletes probably need to obtain 55-60% of their daily calories from carbohydrates. Most people can do this if they consume 3 grams of carbohydrate per pound of body weight. However, seriously training athletes probably require 4 grams of carbohydrate per pound body weight, or 60% of their calories from carbohydrate. For example, a 150 pound person who is cycling, say, 300 miles per week would require approximately 600 grams of carbohydrate daily. This carbohydrate would provide 2400 calories. Good examples of high carbohydrate foods are breads, cereals, grains, pasta, vegetables and fruits.

Each time you exercise muscle glycogen becomes depleted to some extent. By providing high carbohydrate intake every day, it more likely that you will restore the carbohydrate which has been used, thereby allowing for another hard bout of training the following day.

Although we typically think of endurance athletes as having high carbohydrate needs during exercise, other sports such as soccer have been shown to significantly drain stored glycogen. For example, studies have shown that muscle glycogen was depleted to less than a quarter of its preexercise levels after one soccer game. Most of this loss occurred during the first half of the game [Karisson]. Furthermore, supplying carbohydrate during events such as soccer games may help to spare muscle glycogen and increase performance, particularly during the second half.

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Timing of Carbohydrate

This raises the question of timing of carbohydrate intake. If the carbohydrate is to be taken during exercise it should probably be in beverage form. Beverages may be more quickly absorbed than solids and present less potential for stomach upset. A sports-type drink that has a concentration of 6-8% carbohydrate is likely to be easily absorbed during exercise. Most people can tolerate 1/2 cup to 1 cup of liquid every 20 minutes. This tolerance depends upon the individual and the type of exercise performed. Jostling sports like running are associated with more complaints of gastric distress after drinking than are sports such as cycling.

To avoid hypoglycemia or low blood sugar during exercise, carbohydrate should probably not be consumed within 1 hour of the start of exercise. The best pre game strategy is to eat a light meal which contains 100 or so grams of carbohydrate 3-4 hours prior to exercise. Such a meal might look something like this:

	Food	Carbohydrate Grams	Calories
	Skim Milk, 1 cup	12	80
	1 Bagel, 4 ounces	60	320
	'Light' Cream cheese, 3/4 ounce	1	45
	Orange juice, 1/2 cup	15	60
	Water, 16 ounces	0	0
	TOTAL	88	505

In addition, one of the best times to provide carbohydrate to the body is immediately after a workout. Immediately after exercise the muscle is most avid to restore the glycogen it has used during exercise. Perhaps the best way to restore glycogen is to keep a drink which contains carbohydrate in your gym bag, and drink it prior to leaving the locker room or before you hit the shower at home. Alternatively, you can eat a high carbohydrate food, such as bread, bagels, pretzels, or fruit. The goal is to consume at least 50 grams shortly after exercise.

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Carbo Loading

Athletes will sometimes eat a pasta dinners the night before competition and believe that they have "carbo loaded". As you will see in a moment carbo loading is far more difficult to acheive than simply eating one meal high in carbohydrates.

Occasionally it may be prudent to supersaturate the muscle cells with glycogen. This is done by "carbohydrate loading" and is of value if you plan to compete in an event which will last for at least 90 minutes and which will lead to exhaustion or near exhaustion. Carbo loading actually entails a weeks worth of preparation: beginning a week prior to the event exercise is cut by 50% every second day, thus sparing the depletion of glycogen. This will also allow for complete rest the day or two prior to competing. With four days to go the diet is increased to approximately 70% carbohydrate. For most people this would mean eating about 4 grams of carbohydrate per pound body weight.

According to this formula, a 150 pound person would therefore be required to eat 600 grams of carbohydrate per day during the loading period. This is a lot of carbohydrate!