Muscle glycogen concept

The importance of carbohydrates as an energy source during endurance training is known for 60 years. With the advent of needle muscle biopsy in the 1960s, it was found that the main source of carbohydrates during exercise are the glycogen reserves. It was shown that the capacity between 65 to 75% VO2max exercised at intensities of pre-exercise glycogen levels in the muscle bound, ie more glycogen reserves, more exercise time to exhaustion. Because of the critical importance of muscle glycogen during prolonged, intense exercise, a considerable amount of research has been conducted in order to design the best diet to increase muscle glycogen stores prior to the competition and the most effective means of replenishment quickly determining the glycogen after training. The rate determining step in the glycogen synthesis is the transfer of glucose from uridine diphosphate-glucose on an amylose chain. This reaction is catalyzed by the enzyme glycogen synthase, which in a glucose 6-phosphate-dependent, inactive form (form D) and an active form of glucose 6-phosphate can independent (I-form) exist. The conversion of glycogen synthase from one form to the other is controlled by phosphorylation-dephosphorylation reactions. The concentration of muscle glycogen can vary greatly depending on the level of conditioning, exercise routines and diet. The pattern of muscle glycogen re-synthesis after exercise-induced exhaustion is biphasic. After completion of movement and adequate glycogen muscle carbohydrate consumption is rapidly resynthesized to close before training levels within 24 hours. Muscle glycogen then increased very gradually to normal in the coming days. A contribution to the rapid phase of the re-synthesis is to increase the proportion of glycogen synthase I, an increase in muscle cell membrane permeability to glucose and an increased sensitivity of muscle to insulin. The slow phase of the glycogen synthesis is under the control of the intermediate form of glycogen synthase, which is very sensitive to the activation of the glucose 6-phosphate. The conversion of the enzyme can be attributed to this intermediate to form a plasma insulin concentration elevated after several days of high consumption of carbohydrates constantly exposed to muscle tissue. For optimal performance of the exercise, muscle glycogen stores must be replenished on a daily basis again. For athletes daily average endurance of a carbohydrate consumption of 500 to 600 g is required. This leads to a maximum glycogen from 80 to 100 micromol / g wet weight.