During the increased load for 90-120 minutes at 70% V02max (for example, marathon) the muscle glycogen stores gradually decrease. When they reach the critical level (the point of glycogen depletion), the high intensity load does not follow, because the athlete is exhausted and must either stop training or radically reduce their intensity. Exhaustion of muscle glycogen is a recognized limitation of endurance. Athletes using the method of supercompensation of glycogen (carbohydrate load), can almost double the supply of muscle glycogen.
The carbohydrate loading technique was originally a weekly regimen, which began with a series of grueling exercises one week before the start of the competition. Over the next three days, the athlete was on a low-carb diet, but continued to exercise, lowering further the level of muscle glycogen. For three days before the competition, the athlete significantly reduced the amount of training loads and was on a high-carbohydrate diet, which helps to supercomplement the glycogen. This regime contained many shortcomings. Reduced carbohydrate intake often caused hypoglycemia, ketosis and related nausea, fatigue and irritability. Manipulations with diet have been burdensome for athletes.
The revised carbohydrate loading method, proposed by Sherman et al., Has eliminated many of the problems. Six days before the competition, the athlete trains for 90 minutes at 70% V02 max, for 5 and 4 days - 40 minutes at 70% V02max, for 3 and 2 days - 20 minutes at 70% V02 max and the day before the competition he rests . During the first three days the athlete is on a normal diet, providing consumption of 5 grams of carbohydrates per 1 kg of body weight per day. Over the past three days, he uses a high-carbohydrate diet, which gives 10 grams of carbohydrates per 1 kg of body weight per day. The last three days, when an athlete consumes a high-carbohydrate diet, is the real "loading" phase of the regime. As a result of the modified mode, muscle glycogen stores become equal to those provided by the classical carbohydrate load regimen.
In a field study conducted by Karlsson and Saltin, runners participated in a 30 km race after consuming a normal and high-carbohydrate diet. A high-carbohydrate diet provided a level of muscle glycogen, equal to 193 mmol-kg compared to 94 mmol-kg, obtained with a normal diet. All runners passed the distance faster (about 8 minutes), if they started a race with a high level of muscle glycogen. The carbohydrate load enables the athlete to withstand an intensive load longer, but in the first hour of the competition the speed does not affect.
Endurance training promotes supercompensation of muscle glycogen by enhancing the activity of glycogen synthase, the enzyme responsible for the accumulation of glycogen. The athlete must be trained for endurance, otherwise the regime will not be effective. Since glycogen stores are specific to groups of working muscles, the exercises leading to the depletion of these stocks should be the same as in the competitions in which the athlete participates.
High-carbohydrate liquid supplements manufactured by the industry can be given to athletes if they have difficulty in consuming a sufficient amount of carbohydrates with food. Athletes suffering from diabetes or hypertriglyceridemia may have complications in carbohydrate exercise. Before moving to a workload, they must obtain a doctor's permission.
Each gram of accumulated glycogen requires additional water. Sometimes some athletes feel stiffness and heaviness associated with an increased supply of glycogen, but with physical activity these feelings usually disappear.
Carbohydrate loading will help only athletes engaged in intensive endurance exercises, lasting more than 90 minutes. Excessive reserves of glycogen will not allow the athlete to perform exercises more intensively for a shorter period of time. Stiffness and heaviness associated with an increased supply of glycogen may worsen the results of shorter loads, such as 5 and 10 km races.
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