In several past issues of Applied Metabolics, I have discussed carbohydrate loading for bodybuilders. Carbohydrate loading (CL) or simply carb loading, was first developed by Scandinavian sports scientists in 1967. It was not developed initially for bodybuilding purposes, but rather to aid the performance of long-distance running and other extended endurance sporting activities. The idea of carb loading was based on the fact that the primary limiting factor in endurance activity was muscular fatigue, followed by dehydration. The primary cause of the fatigue experienced during long-distance events was a depletion of muscle glycogen stores. Glycogen is stored to a limited degree in the liver and muscle. The glycogen stored in the liver is used to maintain vital blood glucose levels within a safe range. The glycogen stored in muscle differs from that stored in the liver because muscle glycogen can only be used by the muscle that it's stored in. Liver glycogen can be degraded by glycolytic enzymes in the liver, allowing the resulting glucose to be passed into the blood. Muscle lacks the enzyme needed to break down and release stored glycogen into glucose and sent into the blood. As such, when muscle glycogen stores in muscle become depleted, such as through extended activity, that muscle is more or less finished in relation to athletic performance. Indeed, athletes have a term for muscle glycogen depletion. They refer to it as "hitting the wall," because that's what it feels like. If you ever view long-distance endurance events on television, you will inevitably see a few athletes who are experiencing hitting the wall. They lack muscular coordination and appear to be drunk. For them, only sheer willpower gets them over the finish line, and in some cases, they are reduced to literally crawling over the finish line.
Clearly, most bodybuilders do not engage in long-distance athletic events. If they did, they likely would lose sufficient amounts of muscle to disqualify them from ever competing in any bodybuilding competition. That raises the question of why bodybuilders would ever engage in carbohydrate-loading techniques. The answer is that although bodybuilders are not long-distance track athletes, they do store glycogen in their muscles. Glycogen itself is nothing more than a large branched-chain carbohydrate. It can be considered a complex carbohydrate because it contains thousands of branched glucose chains. The primary fuel for anaerobic exercises, such as typical bodybuilding workouts, is muscle glycogen. However, while athletes who participate in long-distance sports nearly deplete their muscle glycogen stores at the end of the race, with bodybuilding workouts that rarely occurs. The only way that a bodybuilder would deplete muscle glycogen stores comparable to that of long-distance athletes would be if the bodybuilder trained for about 6 straight hours and did hundreds of sets and reps. But training in this manner would result in gross overtraining that would result in a loss of muscle mass, not gains . . .