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Although research has shown that ingestion of carbohydrate (CHO) and fluids can improve performance, this is not necessarily true for all individuals in all situations. The amount of fluid and the amount of CHO that should be ingested are dependent on the goals of the individual, the nature and duration of the event, the climatic conditions, the pre-event nutritional status, and the physiological and biochemical characteristics of the individual. The circumstances of each athlete, each sport and each competition must therefore be considered when choosing what or whether to eat and drink; it is not possible to give ‘one size fits all’ advice. In a few situations, athletes can get it wrong, and performance can suffer if the type or amount of food and fluid ingested are inappropriate. Drinking too much may be even more harmful than drinking too little (Hew-Butler et al. 2008). Inappropriate intake of nutrients can also contribute to gastrointestinal problems during exercise, and the symptoms can be so severe that they will have an adverse effect on performance. Personalisation of sports nutrition for performance, and to support training and promote recovery and adaptation, is therefore required.

Food and fluid consumed during competition are part of a specific short-term nutritional strategy aimed at maximising performance at that particular time. When choosing foods and fluids to be consumed during competition, there is no need to take account of long-term nutritional goals, except perhaps (and even then to a limited extent) in extreme endurance events such as the Tour de France or in multi-day running events. In the Tour de France, prolonged exercise is performed daily over about 21 days and the food consumed during each day’s competition may account for about half of the total daily intake (Saris et al. 1989), but even this extreme event lasts for only 3 weeks. In the majority of competitive situations, a balanced diet is not the primary objective of sport nutrition and intake is targeted at minimising the impact of those factors that are responsible for fatigue and impaired performance. It is also recognised that sports nutrition practices and strategies during training may differ from those of competition, depending on the goals of the athlete. For example, training in a state of compromised muscle glycogen (‘train low’) is attracting interest in the research and applied sporting world (this and other similar ‘periodisation’ topics are discussed in Chapters 15 and 16).

New information continues to emerge, and this sometimes changes our understanding of the needs of athletes and the advice that is given to them. These new insights, however, have not resulted in fundamental changes in our understanding, and the challenge is more to provide athletes with the available information in a useful format than to generate further confirmations of what we already know. The most recent fluid replacement guidelines from the American College of Sports Medicine (Sawka et al. 2007...

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