Preparing yourself for endurance sports This guide is addressed to endurance athletes in sports like marathons, triathlons, cycle and mountain bike races, cross country running and skiing. Whatever your sport, a good diet will provide adequate nutrients to improve training efficiency, enhance performance in competition and support optimal recovery. Content Nutrition during training Achieving energy and fluid balance Dietary carbohydrate intake Hydration Nutrition immediately before and during the race Nutrition before the race Nutrition during the race Recovery after the race 3 5 7 11 17 19 21 25 Nutrition during training Energy sources in body evolve with duration of exercise 100 Muscular Triglycerides Energy Sources (%) Muscular Glycogen 50 Blood Glucose (from the liver) Blood Fatty Acids (from adipose tissue) 0 0 1 2 3 Proteins 4 Duration of Effort (hours) During prolonged, low intensity exercise, with no external source of glucose provided, the balance of energy coming from different sources in the body changes markedly, progressively using more body fat. Nutrition during training 5 Achieving energy and fluid balance Athletes often spend hours in daily training and competition where they expend large amounts of energy. It is thus very important to maintain an energy balance by matching this energy expenditure with total energy intake from food. Energy comes from carbohydrates, proteins, fats and alcohol in food and fluids. Carbohydrate is the main fuel for exercise, especially for prolonged or highintensity exercise when rates of body fluid loss are high due to the sweating needed to dissipate body heat produced. Low carbohydrate stores in the body and just a small degree of dehydration (2% body mass loss, or 1-2 kg) lead to fatigue and impaired performance. Hence the importance of a nutritional strategy that will minimize carbohydrate depletion and dehydration. This means ensuring adequate dietary carbohydrate and fluid intake, along with periods of rest between training sessions and in the days leading up to a competition. Carbohydrate rich foods that provide approximately 50 grams of carbohydrate 750 ml of a sports drink 2-3 slices of white bread 1 PowerBar 50 grams of Cornflakes 200 grams of boiled spaghetti 1-2 apples 2 medium ripe bananas 3-4 medium pancakes 2 cereal bars 1 jam sandwich Nutrition during training 7 Dietary carbohydrate intake The carbohydrates that generate energy come from foods and drinks and/or from glycogen stored in limited amounts in the liver and muscles. Glycogen – long chains of glucose molecules – is the natural storage form of carbohydrate in the body. Also, some 15 to 20 grams of glucose is present in the blood. The goal of carbohydrate ingestion is to maximize the body‘s internal carbohydrate stores. High carbohydrate diets can push up muscle glycogen concentrations by 100-150% above normal levels and this can be beneficial for endurance performance. Recommendations on dietary carbohydrate intake are found in the tables on the following page. Different diets influence build-up of muscular glycogen 5 4 Possible Duration of Work (h) High-carbohydrate diet 3 2 Mixed diet 1 Diet rich in lipids and proteins 0 0 1 2 3 4 5 Muscular Glycogen (g/100 g Muscle) Possible duration of effort depends on muscular glycogen content immediately before exercise. A diet rich in lipids and proteins, gives low glycogen and limits duration of effort. A carbohydrate-rich diet increases glycogen and duration of performance. The surfaces represent individual differences with the same diet. Nutrition during training 9 Carbohydrates are especially important in the week before a competition, combining an exercise taper with a high carbohydrate intake (8-12 g of CHO per kg BM/day) to build up muscle glycogen stores. Most athletes need 36-72 hrs for a full carbohydrate load. The pasta party on the day before a race is a popular form of carbohydrate loading. Daily dietary carbohydrate intake goals Minimal physical activity (<3 hours/week) Light physical activity (3-5 hours/week) Medium physical activity (10 hours/week) Professional/elite athletes CHO loading for a cycling marathon 2-3 g CHO per kg BM 4-5 g CHO per kg BM 6-8 g CHO per kg BM >8 g CHO per kg BM 8-12 g CHO per kg BM CHO = carbohydrate; BM = body mass. Adapted from Burke et al. PowerBar Brochure, AIS. Nutrition during training 11 Hydration Dehydration will impair endurance performance, reducing physical and mental function and increasing risk of heat-induced ailments. Sweat losses vary widely from one person to another, and also depend on weather conditions, exercise intensity and body size. Athletes must take measures to avoid body water deficiency and its adverse effects. This means drinking. The sensation of thirst, in response to signals from the brain, triggers the desire to drink. But when you feel thirsty, it is too late. Dehydration has already begun. Athletes should therefore take in enough fluid to prevent thirst setting in. Before starting training, 300-500 ml of fluid is recommended, followed by small, regular amounts of fluid during the exercise, e.g., 100 ml every 10 min. Drink temperature and type affect voluntary intake of liquid 100 Sugared Water Still Water Voluntary Rehydration (%) Denatured Water Cold Drink (15˚ C) 50 Warm Drink (40˚ C) Pleasant Neutral Unpleasant Decrease of pleasant taste 0 Flavour and temperature of drinks influence the degree of voluntary rehydration. During a 6 hour walk at 40°C, participants drank more water when the flavour was pleasant and the drink cool, thus more effectively combating dehydration and heatstroke. Nutrition during training 13 The choice of beverages largely depends on the specific demands for replacement of water, carbohydrate and electrolyte imposed by a given event. If it is hot and sweat losses are high, a hypotonic or isotonic carbohydrate, electrolyte drink is best. In cold weather, you need a more concentrated carbohydrate drink that supplies the energy needed by working muscles. Training is the time to experiment with different drink strategies and with different beverages (and food) to develop an optimal and comfortable strategy for the event. It also offers a means to estimate sweat losses in different weather conditions, by measuring body weight before and after training. Calculation of sweat loss: Body weight before exercise (kg) + fluid intake during exercise (litre) – body weight post-exercise (kg) = Body weight should be measured in minimum clothing and after going to the toilet. Nutrition during training 15 The body also loses electrolytes as you sweat, which must be replaced to maintain fluid balance, but this may be more important after rather than during exercise. However, sodium replacement may be necessary during very prolonged training with very high sweat losses. This is best done with a commercially available sports drink (40-80 g carbohydrate and 450-700 mg sodium per litre). This will rehydrate the body, replace lost electrolytes and provide carbohydrate for energy. Nutrition immediately before and during the race Training influences efficiency of use of muscular glycogen 2 Glycogen Content of Muscle (%) 1.5 Trained 1 Untrained 0.5 Fatigue 0 Duration of Effort Trained athletes build up greater levels of muscular glycogen and use these resources more efficiently. Nutrition immediately before and during the race 19 Nutrition before the race Pre-exercise carbohydrate ingestion can enhance carbohydrate availability by increasing body glycogen stores, or by providing a source of glucose in the gut for later release into the bloodstream. Ingesting high amounts of carbohydrate (i.e. 150300 g) 2 to 4 h before exercise may be effective for some athletes, but others may prefer a light breakfast or carbohydrate snack 1 to 2 hours before the start of the race, taking on more carbohydrates as soon as the race starts. The carbohydrate meals chosen must be easily digested to prevent gastrointestinal discomfort. This is even more important for carbohydrates consumed shortly before the race (<60 min) because there is less time for complete digestion and absorption of foods. As in training, athletes are generally recommended to drink about 300 to 500 ml of fluid 1.5-2 h before the start of the race. This gives adequate hydration and allows time to excrete excess water. Nutrition immediately before and during the race 21 Nutrition during the race It is well known that carbohydrate consumption during prolonged exercise (>60 min) enhances endurance performance. This has been attributed to better maintenance of plasma glucose concentrations and higher rates of carbohydrate oxidation late in exercise, when muscle and liver glycogen levels are low. The optimal rate of carbohydrate ingestion is not known. Based on oxidation rates of single carbohydrates (<1.0-1.1 g/min), a carbohydrate intake of 60-70 g/h has been recommended. A higher intake may provoke gastric discomfort, while a lower intake may be sub-optimal. In hot conditions, slightly less carbohydrate should be consumed (50-60 g/h) because the oxidation rate is lower. When consuming carbohydrate foods or gels, these should be accompanied by drinking some water (100 ml) to dilute the stomach content. Nutrition immediately before and during the race 23 Athletes should try to limit body mass losses during exercise to 1% of body mass. Here, because of the large variations in sweat rates between individuals, it is difficult to give concrete guidelines for fluid intake. The general advice could be to drink about 100 ml every 10 min. But excessive fluid intake must be avoided as it can cause a life-threatening condition called hyponatremia. Those most at risk are small athletes with low sweat rates and slow competitors who may consume large amounts (up to 8 or 10 litres in an event) of low-sodium or sodium-free drinks (i.e. tap water). Drinks with 450 to 700 mg sodium/litre are better for optimal absorption and to prevent hyponatremia. Recovery after the race Recovery after the race 27 Recovery after exercise calls for replacement of the muscle and liver glycogen energy stores and restoring water and electrolyte balance. For those who participate in events on two or more consecutive days, there may be less than 16 hours between finishing day one and starting day two, so a quick recovery is crucial to maintain optimal performance. The repletion of glycogen is important in any fast post-exercise recovery process. The timing of carbohydrate intake is crucial. The quickest replenishment of glycogen occurs in the first 60-90 min after exercise, so it is recommended to consume carbohydrate as soon as possible in the post-exercise phase. Recovery after the race 29 The most important factor for the rate of synthesis of muscle glycogen is the amount of carbohydrate consumed. The highest rate is achieved with 75-90 g/h of carbohydrate consumed at frequent intervals (every 15-30 min). This allows a maximal rate of storage in the first 4 to 6 hours postexercise. Consuming more than 90 g/h provides no additional storage of muscle glycogen and may give gastrointestinal discomfort. Adding certain amino acids and/or proteins to a carbohydrate supplement can increase glycogen synthesis rates. Optimal glycogen replenishment depends on consuming easily digestible carbohydrate-rich foods (i.e. white bread+jam, rice cakes, sports drinks). If appetite is suppressed immediately after exercise, drinking carbohydrate beverages offers an alternative to solid foods. These also have the advantage of providing fluid for a rapid rehydration. Post-exercise rehydration is best with beverages that have a high sodium content (>1300 mg sodium/l) and the volume of fluid consumed should be at least 150% of sweat loss (= body mass loss). Recovery after the race 31 Depending on the extent of glycogen depletion and provided that at least 8 g CHO/kg BM/day is consumed, glycogen stores can be completely restored within 24 h. Storage in the first 24 h is not affected by the frequency of food intake as long as sufficient carbohydrate is ingested. Practical issues like appetite and the availability of food may determine how much and how often food can be consumed, and whether carbohydrate intake is enough. Since sleeping hours interrupt feeding hours, it is recommended before sleeping to ingest approximately 200 grams of easily digestible carbohydrate rich food so as to attain a total carbohydrate intake of 8-10 g/kg BM/day over the first 24 h. So now, you know as much as we do. We sincerely hope that these guidelines will help you improve your performance and get more enjoyment out of your sport. But please remember: each one of you is an individual, different to all the others. So like your training, you must develop your own personal nutrition strategy to be at your best every time. Through science based nutrition products and services, Nestlé Nutrition will help enhance the quality of people’s lives by supporting health and providing care for specific consumer groups with special nutrition needs at every stage of life.
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