Why Do Athletes Go In for Glycogen Loading?
Glycogen is the primary energy source for a muscle that was at rest and then starts working vigorously. The energy of ATP hydrolysis derived from glycogen breakdown is initially produced anaerobically, with the lactic acid product being processed back toglucose in the liver. As an athlete becomes well conditioned, the muscle cells have more mitochondria, allowing for more aerobic metabolism of fats and carbohydrates for energy.
The switch to aerobic metabolism takes a few minutes, which is why athletes must warm up before an event. In long-distance events, athletes rely more on fat metabolism than they do in short-distance events, but in any race there is a final surge at the end in which the level of muscle glycogen may well determine the winner.
The idea behind glycogen loading is that if there is more avail-able glycogen, then a person can carry out anaerobic metabolism for a longer period of time, either at the end of a distance event or for the entire event, if the effort level is high enough. This is probably true, but several questions come to mind: How long does the glycogen last? What is the best way to “load” glycogen? Is it safe? Theoretical calculations estimate that it takes 8 to 12 min-utes to use all the glycogen in the skeletal muscle, although this range varies greatly depending on the intensity level. Allowing for loading of extra glycogen, it might last half an hour. Evidence shows that glycogen may be used more slowly in well-conditioned athletes because they exhibit higher fat utilization.
Early loading methods involved glycogen depletion for three days via a high-protein diet and extreme exercise, followed by loading from a high-carbohydrate diet and resting. This method yields a marked increase of glycogen, but some of it then is stored in the heart (which usually has little or no glycogen). The practice actually stresses the heart muscle. There is clearly some danger here. Dangers are also associated with the high-protein diet because too much protein often leads to a mineral imbal-ance, which also stresses the heart and the kidneys. Again, there is some danger. In addition, the training was often nonoptimal during the week because the athlete had trouble performing while on the low-carbohydrate diet and didn’t train much at all during the loading phase. Simple carbohydrate loading without previous extreme glycogen depletion does increase glycogen, but not as much; however, this increase does not risk potential stress to the heart.
Simple loading merely involves eating diets rich in pasta, starch, and complex carbohydrate for a few days before the stren-uous exertion. It is not clear whether simple loading works.
It is certainly possible to increase the amount of glycogen in muscle, but a question remains about how long it will last during vigorous exercise. Ultimately, all diet considerations for athletes are very individual, and what works for one may not work for another.