Proper share of energy-supplying ingredients in the diet, with particular emphasis on carbohydrates.
The body gets energy from food mainly from carbohydrates and fats, and to a much lesser extent from proteins. Carbohydrates should cover 55-65% daily energy requirements, fats should deliver 23-30% energy, and the rest 12-15% it should come from protein, the degree of utilization of the above-mentioned ingredients depends on the type of work performed. During low-intensity efforts, most of the energy needed comes from the oxidation of fats, and only a small fraction of it from carbohydrates. The body fat reserves of even a relatively slim person are large (table 8.1) and lasts for many hours of low-intensity work, therefore there is no need to supplement them, even if the exercise takes a long time. With the increase in exercise intensity, the share of carbohydrates in energy supply also increases, and with very intense efforts they become the basic energy substrate., without fats. Although both fats and carbohydrates have their positive qualities as an energy source, it should be emphasized, that for an intensely training athlete, carbohydrates are the most economical energy substrate. Unfortunately, unlike fats, body resources of carbohydrates are not large, are approx 400 g (table 8.1) and only last for around 1,0-2,0 hours of moderate intensity exercise (70%VO2max), hence the need for their continuous supply with food.
Table 8.1. Systemic resources and the efficiency of energy substrates (wg Wilmore i Costilla, 1994).
The diet of a young athlete should be high in carbohydrates, with a moderate fat content. There is much evidence that a high-fat diet may have an adverse effect on an athlete's physical performance. The most important and most frequently mentioned negative effects of eating a high-fat diet are a significant reduction in glycogen stores in muscles and liver., accelerating the development of fatigue, especially with high-intensity efforts. In conditions of low consumption of carbohydrates, with intense efforts, protein utilization may increase (gluconeogenesis) for energy processes, which is a very unfavorable phenomenon for the body. Another negative effect of eating too much fat is the increased need for oxygen. Because to get the same amount of energy, the oxidation of fats requires approx 10% more oxygen than carbohydrate oxidation. Moreover, research shows, that athletes on a high-fat diet find their efforts more strenuous (subjective assessment according to. shall Pay) compared to those on a high-carbohydrate diet.
About 60% energy from carbohydrates in the diet of a young athlete means daily consumption of this nutrient in an amount 8-10 g for every kilogram of the competitor's body weight. Such a large supply of carbohydrates requires frequent inclusion of products rich in this nutrient in the diet. High-carbohydrate foods should be present in virtually every athlete's meal consumed during the day. Listed below are products and foods that are good sources of carbohydrates:
• bread, mainly wholemeal and breakfast cereals,
• rice, groats, corn and other grain products,
• pasta, noodles and other flour dishes,
• both fresh and dried fruit,
• sweet dairy products (yoghurts and fruit smoothies),
• honey, jam, jam,
• carbohydrate drinks (fruit juices, sports drinks),
• small high-carbohydrate snacks between meals (e.g.. bars made especially for sportsmen or made on the basis of dried fruit and cereals).
A diet rich in carbohydrates should apply to the athlete in all periods, both preparation and pre-competition, as well as during and after the competition.. In the preparatory period, carbohydrates consumed regularly during training, prevent fatigue by maintaining normal blood glucose levels, and supplemented right after the end of training, they ensure a faster renewal of the used glycogen resources in muscles and in the liver. Within a few days before the start, eating a diet rich in carbohydrates (with a gradual reduction of training loads) allows you to accumulate significant amounts of muscle glycogen (the so-called. glycogen supercompensation). In the meal immediately preceding the start, the intake of carbohydrates is recommended in order to increase their intracorporeal reserves, and in the course of the starting effort itself (lasting longer than 45 minutes) prevent fatigue, by conserving glycogen in both muscles and the liver. Carbohydrates are also recommended after the competition because, just like after training, they determine the optimal pace of glycogen renewal, which takes on a special meaning, when the competition lasts for several days.
After training or competition, it is best to start taking carbohydrate drinks as soon as possible after the end of physical exertion, because in the first 120 In minutes, glycogen resynthesis is much faster than in the later hours (figure 8.1).
Figure 8.1. Influence of early carbohydrate consumption on post-workout glycogen restoration (wg Ivy, 2001).
In this case, carbohydrates in the form of maltodextrins in an amount of approx 1,2 g / kg body weight per hour, taken in two portions co 30 minutes, although carbohydrate and protein drinks may also be served, then it is recommended to use smaller amounts of carbohydrates – 0,8 g and 0,4 g protein / kg b.w., for an hour, also taken at half-hour intervals.