Carbohydrate is stored in the body in the form of glycogen - By: sulamita berrezi

Carbohydrate is stored in the body in the form of glycogen, primarily in the liver (about 70–100 g in the fed state) and in the skeletal muscles (about 300–500 g, depending on muscle mass and preceding diet). These stores are small relative to the rate of carbohydrate use during exercise. Fat and carbohydrate are the main fuels used for energy supply in exercise. In low-intensity exercise, most of the energy demand can be met by fat oxidation, but the contribution of carbohydrate, and especially of the muscle glycogen, increases as the energy demand increases. In high-intensity exercise, essentially all of the energy demand is met by carbohydrate metabolism, and carbohydrate oxidation rates of 3–4 g min1 may be sustained for several hours by athletes in training or competition. When the glycogen content of the exercising muscles reaches very low levels, the work rate must be reduced to a level that can be accommodated by fat oxidation. Repeated short sprints will also place high demands on the muscle glycogen store, most of which can be converted to lactate within a few minutes. Carbohydrate supplies about 45% of the energy in the typical Western diet: this amounts to about 200– 300 g day1 for the average sedentary individual, and is the amount that is necessary to get through normal daily activities. In an hour of hard exercise, up to 200 g of carbohydrate can be used, and sufficient carbohydrate must be supplied by the diet to replace the amount used. Replacement of the glycogen stores is an essential part of the recovery process after exercise; if the muscle glycogen content is not replaced, the quality of training must be reduced, and the risks of illness and injury are increased. Low muscle glycogen levels are associated with an increased secretion of cortisol during exercise, with consequent negative implications for immune function. Replacement of carbohydrate should begin as soon as possible after exercise with carbohydrate foods that are convenient and appealing, and at least 50– 100 g of carbohydrate should be consumed within the first 2 h of recovery. Thereafter, the diet should supply about 5–10 g of carbohydrate per kg body mass, including a mixture of different carbohydrate-rich foods. For athletes preparing for competition, a reduction in the training load and the consumption of a high carboydrate diet in the last few days are recommended: this will maximize the body's carbohydrate stores, and should ensure optimum performance, not only in endurance activities, but also in events involving short-duration highintensity exercise and in field games involving multiple sprints. The high-carbohydrate diet recommended for the physically active individual coincides with the recommendations of various expert committees that a healthy diet is one that is high in carbohydrate (at least 55% of energy) and low in fat (less than 30% of energy). However, where energy intake is either very high or very low, it may be inappropriate to express the carbohydrate requirement as a fraction of energy intake. With low total energy intakes, the fraction of carbohydrate in the diet must be high, but the endurance athlete with a very high energy intake may be able to tolerate a higher fat intake.

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