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Table 16.1 The goals of sports nutrition. Everyday nutrition goals

Continue to enjoy food and the pleasure of sharing meals. Keep healthy especially by looking after the increased needs for some nutrients resulting from a heavy training programme. Get into ideal shape for their sport achieve a level of body mass, body fat and muscle mass that is consistent with good health and good performance.

Refuel and rehydrate well during each training session so that they perform at their best out of each session. Practise any intended competition eating strategies so that beneficial practices can be identified and fine-tuned. Enhance adaptation and recovery between training sessions by providing all the nutrients associated with these processes. Eat for long-term health by paying attention to community nutrition guidelines.

Source: adapted from Burke and Read (1).

Of equal importance with the science of sports nutrition is its practice. Athletes are often required to meet nutrient intake targets that are beyond the constraints of appetite, gastrointestinal comfort or access to food. Whether chocolate bars are a practical food choice in typical sporting situations, and whether they assist in the achievement of other goals of sports nutrition, is also discussed.

Carbohydrate Intake and Exercise Performance

The availability of carbohydrate for oxidation by the muscle and central nervous system is a critical factor in the performance of prolonged sessions (>6090 min) of submaximal or intermittent high-intensity exercise, and is a permissive factor in the performance of brief high-intensity exercise (for a review, see (2)). However, the total body stores of carbohydrate are limited, and are often substantially less than the fuel requirements of the exercise programmes of many athletes. Carbohydrate intake before, during and in the recovery after exercise provides a variety of options for increasing body carbohydrate availability.

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For competition, the athlete must

In the case of weight-classed sports, achieve the weigh-in target without sacrificing fuel stores and body fluid levels. 'Fuel up' with adequate body carbohydrate stores prior to the event. Minimize dehydration during the event by using opportunities to drink fluids before, during and after the event.

Supply additional carbohydrate during events >1 hour in duration or other events where body carbohydrate stores become depleted. Achieve pre- and during-event strategies without causing gastrointestinal discomfort or upsets.

Promote recovery after competition, particularly in sports played as a series of heats and finals, or as a tournament.

'Fuelling up' before Exercise

Before competition, an athlete should ensure that liver and muscle glycogen stores are able to support the anticipated fuel needs of the event. For sports events lasting less than 60 min, muscle glycogen stores, which have been normalized to the resting levels of trained athletes, are considered adequate (3). In the absence of muscle damage, muscle glycogen levels can be restored by 2436 hours of high carbohydrate intake, in conjunction with a reduction in exercise volume and intensity (4). Thus, 'fuelling up' for most events simply consists of high carbohydrate eating and tapered training on the day before competition. Athletes who compete in events longer than ~90 min may improve their performance by maximizing muscle glycogen stores over the 36 days prior to their competition via an exercise-diet programme known as glycogen (or carbohydrate) loading. 'Loaded' glycogen stores permit the athlete to continue exercising at their optimal pace for a longer time, postponing the onset of fatigue and decreasing the time taken to complete a set task of prolonged duration (3).

The original carbohydrate loading protocol, developed by Scandinavian scientists in the late 1960s, used extremes of diet and exercise to first deplete then supercompensate glycogen stores (5). Recent research suggests that trained athletes do not need to undertake a severe depletion phase to subsequently 'load' glycogen stores. It appears that similar increases in muscle glycogen can be achieved simply by tapering training and consuming a daily carbohydrate intake of ~810 g/kg body mass over the 72 hours prior to an event (6). The most important dietary factor in glycogen storage is the amount of carbohydrate consumed (4) (see 'Carbohydrate and post-exercise recovery' below). Muscle glycogen storage increases in relation to dietary carbohydrate intake, reaching a threshold above which no further storage occurs at a carbohydrate intake of ~500600 g/day or 810 g/kg body mass/day (7).

In theory, a variety of carbohydrate-rich menus may be used by athletes to 'fuel up' before events. However, studies have reported that in real life, athletes do not have sufficient practical nutrition knowledge to achieve such carbohydrate intakes and may require dietary counselling (8). Dietary patterns that may limit total carbohydrate intakes include reliance on three meals per day instead of more frequent food intake opportunities, emphasis on high fibre and bulky carbohydrate-rich foods which may cause gastrointestinal fullness before fuel intake targets are reached, and the failure to recognize sugar and sugary foods as suitable carbohydrate-rich sources (8). Education should promote the advantages of frequent meals and snacks and compact, dietary forms of carbohydrate such as sugar-rich foods and carbohydrate-containing drinks.

A high carbohydrate intake should be a daily routine for athletes who need to promote recovery between prolonged training sessions. In the situation of everyday nutrition, athletes need to choose foods that balance their fuel requirements with total nutrient needs and general energy balance. However,

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