Athletes are always seeking a competitive edge. Frequently, they look to some new diet, food or vitamin to give them that extra advantage. Most nutrient supplementation programs turn out to be useless, and some may even be harmful.
By contrast, carbohydrate loading can actually help--but only in the right circumstances. To know when to use this measure, one must first understand the principle behind it.
During mild to moderate exercise, free fatty acids derived from stored body fat are the main source of energy for working muscles. But as the intensity and/or duration of the activity increases, the supply of oxygen to the tissues dwindles. The body then relies increasingly upon carbohydrate, which uses less oxygen than fat does as it is converted to energy.
In the body, carbohydrate is stored as glycogen, primarily in muscle tissue and in the liver. We have relatively large quantities of fat, but only small reservoirs of glycogen. This is important to the athlete because muscle fatigue is believed to be directly related to the depletion of muscle glycogen. Theoretically, then, the larger the available carbohydrate pool, the longer the athlete can exercise before she or he "hits the wall" and has to stop.
Demonstrating the Importance
A fair amount of research has been aimed at finding ways to stockpile carbohydrate. Two paths to this goal have emerged. First, physical training itself stimulates glycogen production, increasing stores by as much as 50%. In addition, these reserves can be further augmented by making changes in the diet.
The importance of diet in this respect was first demonstrated in the late 1960s in a study that compared muscle glycogen levels following three different regimens: high-fat and low-carbohydrate; low-fat and high-carbohydrate, and a normal ratio of the two. The researchers found that the high-carbohydrate diet doubled the level of stored carbohydrate--from 1.75 to 3.5 grams per 100 grams of muscle.
The high-fat diet resulted in the lowest concentration of glycogen, just 0.6 grams per 100 grams of muscle. These levels correlated well with the length of time the volunteers could exercise before becoming exhausted--170 minutes on the high-carbohydrate diet, 115 minutes on a normal diet and only 60 minutes following the high-fat regimen. Further studies indicated that the highest stores could be achieved if reserves were first depleted and then built back up again.
This information led to the development of the carbohydrate-loading programs that are in vogue among many athletes today. In general, the procedure has included a period of muscle-glycogen depletion by vigorous exercise coupled with a diet high in protein and fat, and then followed by a rest and replenishment of muscle glycogen with generous amounts of dietary carbohydrates.
Recent studies have suggested that it is unnecessary to use the high-fat diet during depletion to achieve maximal glycogen stores during refeeding. In fact, this may actually impair performance. Thus, the procedure has been altered to include normal carbohydrate intake during depletion.
So far, research has barely touched on the question of whether one carbohydrate is better than another. But one fact is clear: Natural foods containing complex carbohydrates provide essential vitamins and minerals, rather than just calories.
As simple as it seems, carbohydrate loading is not without side effects. It should definitely not be used indiscriminately. Besides the increase in glycogen, there is an upsurge in the water content of the muscles. That can translate into a weight gain of as much as six pounds and can affect performance directly. The added water can also cause muscle stiffness, which can impair ability.
Some individuals seem to tolerate the procedure better than others. People with diabetes/hypertriglyceridemia are advised to avoid carbohydrate loading altogether because it alters carbohydrate and fat metabolism in ways that can exacerbate their conditions.
Trainers, coaches and athletes must understand that carbohydrate loading provides endurance, not strength. It is effective only in sports such as long-distance running, cross-country skiing and cycling--competitions in which the exercise continues for more than two hours at a time. A football game may last longer than two hours, but the individual players are involved only a fraction of that time, and the conditioned athlete has more than enough glycogen to see him or her through to the end.
Even for those sports where it is indicated, experts advise that carbohydrate loading be used only occasionally--once or twice a year for big events.
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