There have been many studies that have shown "endurance performance correlates with carbohydrate stores" (muscle glycogen), and that fatigue occurs when these stores are used up. Most athletes are aware of glycogen depletion and describe it as "hunger knock" or "bonk". Since it is impossible to burn fat anaerobically, high intensity workouts deplete the body of carbohydrate rapidly. It is possible to deplete carbohydrate stores with as little as 20 minutes of interval training. So carbohydrate is important for both power and endurance athletes. This is why it is important to have a diet that is high in complex carbohydrate and why many athletes have adopted the strategy of carbohydrate loading.

Recent work has shown that it is possible for trained athletes to achieve an increased carbohydrate store by tapering training and increasing carbohydrate intake in the days preceding competition. The only major problem with this is physically eating the required quantity of carbohydrate. This is usually more than that with which the athlete feels comfortable. 600g per 24 hours is required e.g. 3 kg of potatoes! PSP22 has been recommended as a more palatable way of ingesting the required amount of carboydrate without eating too much fat or protein. Depletion loading regimes, where by athletes deprive themselves of carbohydrate and continue to train in order to fully deplete their carbohydrate stores, before ìsuper-compensatingî with a high carbohydrate diet are no longer recommended.

Latest research has shown that it is much more important to keep blood sugar levels high during exercise with a regular supply of carbohydrate energy drinks and gels, in order to improve performance. Energy drinks and gels provided during exercise help to maintain blood glucose levels, which helps access more of the scarbohydrate stored in the muscles. Once blood glucose levels start to fall, fatigue sets in and performance suffers.