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Abstract
Lecture 23
It is well documented that exercise performance is greatly influenced by nutrition. The key factor in coping with the heavy demands of exercise faced by elite athletes seems to be carbohydrate intake. Carbohydrate recommendations range from 6–10 g/kg of bodyweight depending on gender and physical fitness level of the individual, total training load, energy expenditure, type of physical activity and environment.
Although carbohydrate rich diets were recommended in the past, specific recommendations in percentages should be used with caution. For example, in a 5000 kcal diet, a 50% of energy in carbohydrates will provide 7–8 g/kg of bodyweight for a 70 kg athlete. On the contrary, a 60% in carbohydrates diet will provide only 4–5 g/kg of bodyweight for a 60 kg athlete.
The proportional increase in carbohydrate requirement increases accordingly the proportional need in number of servings for carbohydrate-based food groups. Thus, many athletes should exceed the upper range of servings for these food groups, that is: (A) bread-cereals-legumes: more than 10 servings/day, (B) vegetables: more than 5 servings/day, (C) fruits: more than 4 servings/day, (D) milk-alternatives: more than 3 servings/day. Athletes with lower energy needs of small body shape are advised to select nutrient-dense foods in order to obtain adequate carbohydrates.
Athletes seem to benefit from 200 to 300 g of carbohydrates consumed 3–4 h before the athletic event. Pregame meal targets to prepare the athlete for the upcoming event, providing him with carbohydrates, electrolytes and water. Carbohydrates are essential to maintain blood glucose levels and maximise glycogen stores. There is a dispute whether glycaemic index of carbohydrates influences performance.
During exercise athletes should consume 30–60 g carbohydrates per hour (or 0.7 g/kg of body weight) in order to maintain blood glucose levels. This is of extreme importance when the event lasts more than an hour and it takes place in extreme environmental conditions (cold, heat or high altitude).
After exercise athletes should consume 1.0–1.5 g/kg of bodyweight during the first half hour and again every 2 h for 4–6 h in order to replace liver and muscle glycogen stores.
Carbohydrate intake can enhance training capacity and may consist the trigger point for winning an event and achieving the best possible performance.