Carbohydrate Loading

old message Carbohydrate Loading Darrell Miller 10/17/06

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Date: October 17, 2006 01:50 PM
Author: Darrell Miller (
Subject: Carbohydrate Loading

Carbohydrate loading is an ergogenic technique devised for endurance athletes to trick the muscles into storing more fuel than it normally would. Although carbohydrate loading has been hailed as an innovative training technique in the past few years, the discovery of carbohydrates as the preferred fuel of the body dates back several decades. In 1939 two scientists named Christiansen and Hensen demonstrated that the body burns carbohydrates before drawing upon its fat and protein. The research found that the body readily uses carbohydrates as fuel for the muscular and nervous system with minimal wastage and toxic by products – unlike the case with protein and fats.

The body stores carbohydrates in the form of glycogen in the muscles and liver. This glycogen helps the liver to detoxify otherwise dangerous substances. It also supplies a readily available source of glucose to maintain the essential blood sugar level. Glycogen stored in a muscle is available for energy use for only that particular muscle, unlike glycogen stored in the liver, which is available systemically. At rest, and during low-intensity exercise, the body burns about an equal mixture of fat and carbohydrate for energy purposes. However, as work intensity increases, carbohydrates become the dominant fuel because of its quick availability. Laboratory research has shown that an exercise intensity of less than 40-50 percent VO2 max, the body burns mostly fat, and the degradation of stored glycogen is minimal.

The situation changes during high intensity exercise, when carbohydrates become the sole source of energy. The activity itself is limited by the availably of glycogen as an energy source.

Muscle glycogen is five times more available as an energy source for intensity exercise as compared to liver glycogen. When the muscle glycogen becomes depleted, the muscle its self begins to fail, and fatigue rapidly sets in marathon running, this dreaded phenomenon is known as “hitting the wall”.

Since it is obvious that the availability of glycogen is a limiting factor in endurance athletic events, exercise physiologists devised ways to increase glycogen storage in the body. In 1967 two Swedish exercise physiologists came up with carbohydrate loading, also called glycogen loading, as a method of supper-compensation of glycogen through diet and exercise.

Hydrate loading usually is approached by any of the following means:

  • Consumption of high (complex) carbohydrate and high protein foods while limiting intake of refined sugars, 3-4 days before competition. This results in a glycogen level 40-60 percent above normal.
  • Exercise to exhaustion for several days, followed by a carbohydrate-loading period. This will deplete stored glycogen and then double its reserves.
  • A combination of low carbohydrate consumption and exhaustive exercise. The athlete eats only proteins and fats for 3 days, followed by eating only carbs for the next 3 days. On the carbo-concentration days, the athlete exercises minimally, so as not to interfere with the glycogen storage process.

According to researchers David Costill, Ph.D., carbohydrate consumption in excess of 600 grams daily won’t result in proportionally larger amounts of synthesized glycogen. In the first 24 hours of carbo-loading, the type of carbs eaten is not of critical importances. However, after the second day, Costill suggests eating complex rather refined or simple sugars.

Complex carbs are those which contain lots of intact fiber, such as whole grains, fruits and vegetables. An exception to this rule is pasta, which is a refined sugar but is good to ingest during carbo-loading. Complex carbs tend to maintain a steady output of the hormones insulin, which activates the enzymes glycogen synthetase, essential for effective glycogen storage.

Most experts today advocate a gradually tapering exercise program while increasing carbo consumption to about 525 grams daily. This avoids the problems associated with the low-carb period, such as fatigue, weakness, potassium loss and muscle tissue loss.

One day prior to competition, the athlete rests completely and consumes about 550 grams of carbohydrates.

The carbohydrate loading program should be limited to three times a year. More often than seems to decrease its effectiveness. Costill suggests that athletes engaged in intense exercise on a daily basis consume about 70 percent of their daily calories in carbohydrates. This will maintain adequate glycogen levels in both the liver and muscles, according to Costill.

Carbohydrate loading is of no real benefit in athletic events lasting less than 60 min, because lesser activity time does not deplete glycogen levels enough to inhibit work capacity of endurance.

Carbohydrate loading isn’t for everyone. Each gram of cellular glycogen is stored with 2.7 gram of water. This rapid water storage makes some people feel stiff and tight, resulting in decreased performance. The only way to determine if the carbohydrate loading works for you is to try it – carefully!

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