Optimally, athletes should ingest a carbohydrate electrolyte drink throughout exercise. It has recently been shown that ingestion of carbohydrate throughout exercise improves performance more than when an identical amount of carbohydrate is consumed late in the exercise period. The ideal nutritional strategy during exercise should: provide sufficient carbohydrate to maintain blood glucose levels and carbohydrate oxidation provide water and electrolytes to prevent fluid imbalance not cause any gastro-intestinal discomfort taste good. Optimal carbohydrate sources have been mentioned previously and are also discussed in the section on post-exercise recovery below. The effectiveness of a sports drink in supporting fluid balance depends on a number of factors of which carbohydrate and sodium content, and osmolality are very important. The ideal sports drink for carbohydrate and fluid replacement should have a relatively low carbohydrate content of between 40 and 80 g/l, have an osmolality which is moderately hypotonic to isotonic, and have a sodium content of between 400 and 1200 mg/l. Individual sweat loss can be estimated from weight loss. By regularly monitoring nude body weight before and after training sessions and competitions, it is possible to predict an individual‘s fluid loss in a certain race under most environmental conditions. Weight loss will be due not only to fluid loss but also to glycogen and fat oxidation; for example, over 90 min of exercise 100-250 g of substrate may be oxidized. However, since the main limitation to maintaining fluid balance appears to be the volume of beverage that can be tolerated in the gastrointestinal tract, in most situations it is advisable to drink as much as possible. Completely restoring sweat losses by fluid consumption may not always be possible because these losses may exceed 2 l/h, and ingestion of such amounts usually cannot be accepted by the gastrointestinal tract. Therefore, the volume of drink that can be tolerated by the intestine usually limits fluid and carbohydrate consumption. This highlights the importance of making ‗drinking during exercise‘ a part of the regular training programme.