3.1 Eating and drinking for performance; before, during and after exercise
During exercise, fatigue may be caused by depletion of muscle glycogen stores and low blood sugar levels. In overall terms, a low-fat diet with plentiful, low GI (glycaemic index) carbohydrates and a suitable amount of protein and plenty of vitamins and minerals is most suitable for athletes. Hydration is also very important and it is considered later in this course. To prepare for exercise, high-carbohydrate meals and snacks are needed to maximise stores. The pre-exercise meal should be taken around two hours before exercise and should consist of low to moderate GI carbohydrates with small amounts of protein and some vitamins and minerals, for example, a chicken salad sandwich made with wholemeal bread. Both immediately before and during exercise which lasts for more than one hour, carbohydrate foods with a high GI value will delay the time before muscle glycogen stores become depleted.
The important aspect of post-exercise recovery is the replacement of carbohydrate. Depending on the intensity of exercise, 7 to 12 grams per kilogram of body weight per day of carbohydrate are required. Evidence suggests that higher GI snack foods may also be more appropriate immediately after exercise since they promote glycogen storage. Glycogen storage occurs faster in the first two hours after exercise but does not begin until after 1 gram per kilogram of body weight has been consumed (Burke, 2007). Therefore it is very important to refuel quickly, using a suitable snack, when there is limited time between training sessions. One example of a high GI snack providing 75 grams of carbohydrate would be a plain bagel (90 grams) with two heaped teaspoons of jam (Bean, 2006) and this snack would begin the refuelling process. This should be followed by a carbohydrate-based main meal. It is important to begin training sessions in a fully hydrated state and it is crucial to re-hydrate during and after exercise to aid a speedy recovery. It may take several hours to fully hydrate even after a loss of only 2 per cent of body weight due to physical exertion. Since alcohol is a diuretic agent and will interfere with rapid hydration, as well as interfering with recovery, the choice of post-exercise drinks should be carefully considered. Alcohol should be avoided for at least three hours.