Aspekte der korperlichen und mentalen leistungsfahigkeit

Carbohydrates play a special role as energy carriers and, in the form of glucose, are essential as energy source for cell performance especially during muscular activity. A balanced nutrition is of enormous importance during physical activity to maintain or improve performance. During intensive muscle work, carbohydrates are an indispensable source of energy and there is broad consensus that energy used up in physical activity should be replaced principally by carbohydrates. Full glycogen stores prior to training and competition as well as an intermittent uptake of carbohydrates, e.g., as 8- 10% solutions of a mixture of oligosaccharides, sucrose and glucose or as confectionery products, sweetened fruits, etc. are advantageous, especially during longer-lasting work in the region of 70% VO(2max). Accordingly, a contribution to the total daily energy supply of 60 to 65% from carbohydrates is recommended for athletes under intensive training. Long-term stress is limited by the capacity of the organism to take up oxygen (VO(2max)) SO that the 16% or 13% higher energy production from the oxidation of glycogen or glucose, respectively, in comparison to the consumption of fat is highly significant. The glycogen stores in muscle (ca. 300-500 g) and liver (ca. 100 g), corresponding to 1600-2000 kcal are modest in comparison to fat stores (80000 kcal). Furthermore, the energy flow rate from the degradation of glucose or glycogen is about 2- to 5-fold higher in comparison to the oxidation of fat. When the glycogen stores are exhausted, energy is increasingly supplied by the consumption of fat and thus the intensity of performance is reduced. Thus, the maintenance of the blood glucose level plays an important role in delaying the onset of fatigue. It is important to ensure the glucose supply to the musculature by means of a carbohydrate-rich diet as well as sugar-containing drinks, confectionery products, etc., especially when the glycogen stores are empty. The correct time of glucose uptake prior to stress is of major importance. In a roller ski test over 30 km at ca. 75% VO(2max) and 2 hours duration, sucrose (100 g dissolved in 600 ml water) given directly before and during the test resulted in improved performance. In the placebo test, 24% of the subjects gave up with clinical signs of hypoglycemia. The blood glucose level as compared to the placebo group did not decrease under intermittent uptake of sucrose. In addition to that of the muscles, the energy requirements of the central and peripheral nervous systems must also be fulfilled and this occurs almost exclusively via blood glucose. A sufficient blood sugar level is indispensable for the maintenance of central and peripheral nervous functions. A reduced blood sugar level and thus a restricted energy supply leads not only to peripheral but also to central fatigue. Thus, in motorsports, tennis, ski jumping, sky- diving, etc., the concentration-coordination ability is improved by carbohydrates and the incidence of driver errors, especially in tracks with many curves, is significantly reduced. Apart from the nutrition- physiologically and medically recommended ratio of the daily calorie intake of 55-60% carbohydrates, 25-30% fat, and 10-15% protein, especially for athletes, too little attention is paid in general to the further differentiation of the carbohydrates. Since snacks, energy chocolate bars, and other sweet things are readily consumed by athletes before, during, and after physical stress in order to maintain the glucose level or refill the glycogen stores, mono-, di-, and oligosaccharides should be offered in a balanced ratio for this nutritional purpose.