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John North of Centerville is running the St. George marathon in October and wanted information on a technique he had heard about called "carbo-loading" as a means of improving performance.

Carbohydrates are the primary fuel for muscle contraction and the most important nutrient in athletic performance. An athlete's intake of carbohydrates depends on the intensity and duration of their workout; if you are an endurance athlete, you should pay particular attention to your carbohydrate intake.Endurance training often lasts 90 minutes or more and expends 1,000 to 1,400 calories in the process. Endurance athletes should obtain at least 50 percent, and ideally 60 to 70 percent of their calories from carbohydrates.

Even though many athletes understand the importance of carbohydrate intake, their diets often contain less than 40 percent.

Carbohydrate stores in the body are limited. When depleted, athletes experience early fatigue. To maximize performance in the endurance events, it is often beneficial to consume carbohydrates before or during competition.

"Carbo-loading" is an attempt to maximize muscle glycogen stores. The most practical approach to carbo-loading involves training intensely five or six days prior to competition.

During the last 3 or 4 days before the competition, you should gradually reduce the amount of training and eat high-carbohydrate meals (greater than 600 grams) on each of the three days before competing. This increases muscle glycogen stores 20-40 percent above normal.

After one to three hours of continuous exercise, you tire because of carbohydrate depletion. To maximize your endurance, it is often beneficial to consume carbohydrates during competition if your exercise lasts more than two hours.

This can be done by consuming liquid and/or nutritional bars that contain simple sugars or complex carbohydrates.

Your pre-competition meals should be low-fat, and high in carbohydrates (75-150 grams). Eat your meal three to six hours before the activity.

Carbohydrate feedings benefit athletes that engage in endurance sports that deplete glycogen stores. However there is little need for carbohydrate supplementation during non-endurance activities.