Nutritional supplements serve as ergogenic aids removing factors limiting human physical performance. Their ergogenic usefulness enhances a well-balanced diet. Carbohydrates, proteins (amino acids), vitamins, minerals, electrolytes, and trace elements contribute to energy production necessary for maximal oxygen uptake, maximal muscle activity, minimal energy waste, and later onset of fatigue.
Carbohydrate deficiency hinders performance by depriving the muscles the necessary energy source for further exercise and leaves the athlete fatigued and maybe stricken with hypoglycemia, a low blood sugar condition. Chronic depletion of glycogen stores in the muscles leads to reduced speed, precision and endurance. This can be prevented by dietary carbohydrate intake of 500-600 g per day following acute exercise to stimulate proportional glycogen synthesis necessary for energy the next day. In fact, a high-carbohydrate regimen promoted significant 24-hour glycogen rebound. Enhanced muscle glycogen stores allow an athlete to maintain a high work intensity longer, not work faster, during prolonged aerobic exercise.
70% of the calories from carbohydrates is recommended for athletes undergoing hard-training on a day-to-day basis, while maintaining high caloric intake. Many athletes attempt to maximize levels of muscle glycogen by follwing a "loading" or "supercompensation" regimen for long-term training. Essentially, a normal to an undersupplied carbohydrate diet is taken at the beginning of training preceding exhaustive training under the same diet. Then, carbohydrate intake is increased, "loaded", with a concurrent decrease in exercise the following days prior to competition. Rapid synthesis of muscle glycogen, localized in exercising muscles, are twofold, and fatigue is postponed and long-term exercise is enhanced.
Dietary protein is especially needed in intensive and strength training for the support of skeletal muscle. In the absence of protein after the body exhausts its supplies, the body resorts to decomposition of proteins of the liver, kidney, intestinal tract and to the destruction of erythrocytes and plasma proteins for amino acids which may result in sports anemia.
Lack of dietary protein also produces a negative nitrogen balance through bowel movement sweating and urinary losses resulting in a loss of lean body tissue and decreased physical work capacity. Increased protein intake through supplementation provides an adequate amino acid supply for the athlete, especially and most importantly in the early phase of training for the support of strength and power. This includes increases in muscle mass, myoglobin (oxygen storage for "burning" carbohydrates), enzyme content (facilitate energy metabolism), and erythrocyte formation (prevention of anemia). A recommended diet of 2.0g/kg/day (or more, up to 2.6g/kg/day) maintains a level of maximum performance early in training. The dietary protein intake of 2.64g/kg/day based on the physical demands of the athlete's regimen has been shown to secure positive nitrogen balance.
Vitamin deficiences are prevalent in water-soluble vitamins needing to be replaced daily, namely the B-complex and C vitamins. Thiamine (B1), riboflavin (B2), niacin, and pantothenic acid serve as coenzymes in the metabolism of glucose to energy and should be increased as energy expenditure and sweating increases. Pyrodoxine deficiency reduces the utilization of glycogen as an energy source, thereby resulting in reduced oxygen availability to tissues. Deficiencies in folacin or cobalamin leave erythrocytes immature leading to megablasitc anemia. Supplementing B-complex vitamins in a undersupported diet generally results in performance restoration. In contrast to B-complex vitamins, vitamin C (ascorbic acid) affects can be demonstrated in conditions of deficiency. In response to stress, in which physical exercise is a form, vitamin C has been associated with the synthesis to catecholamins and cortisol. Following exhaustive physical exercise, the vitamin C content of the adrenal gland decreases. It was found lower pulse rates during exercise and recovery were maintained upon vitamin C supplementation.
In contrast, fat soluble vitamins, namely A, D and K, usually do not need to be supplemented. However, Vitamin E (alpha tocopherol) supplementation has been examined during exercise. Its function as an antioxidant serves vital in preventing unsaturated fatty acids from being oxidized. A deficiency leads to the decrease in ATP produced per oxygen used and therefore, lack of energy for exercise. Evidence also reveals it may protect the linings of the respiratory tract against air pollutants.
Normally, 10% of the dietary iron is absorbed in a sufficiently supplied diet. However, low iron levels leads to low oxygen intake and inhibition of aerobic metabolism at the tissue level. Athletes excrete more amounts of iron through feces, urine, and sweat (and menses in females) than the average person. Thus, iron supplementation has been shown to maintain adequate iron levels for maximal performance and endurance, and for preventing iron deficiency anemia. Iron deficiency anemia has been shown to lower maximal oxygen intake and physical work capacity, increase the heart rate at submaximal work loads, increases post exercise lactate levels, and prolong the time needed for recovery from exercise. Iron supplementation is beneficial for the iron deficient, but not necessarily anemic, athlete especially in early training when erythrocytes are taken as iron sources. This ensures a restoration of hemoglobin as training progresses.
Water and electrolytes play an integral part in acid-base regulation of body fluids. The extent to which these constituents influence protons and buffering capacity has important implications for setting the limits of physical performance, because acidification of muscle in heavy exercise is believed to powerfully suppress Ca2+ activation of muscle contraction and the enzymatic reactions involved in energy metabolism. Depletion of water beyond 2% of weight will cause significant impairments in thermal and circulatory regulation during exercise essentially leading to decreased endurance proportional to the degree of hypohydration due to sweat loss and a hot environment. Anaerobic function decreases also as sweat loss exceed 5% of weight with deterioration in muscular endurance and power. This results in an increased concentration of electrolytes in extracellular fluids (due to small electrolyte excretion in sweat). It is actually a hypernatremia (and hyperosmolarity) that increasingly impairs exercise thermoregulation as hypehydration progresses. Fluid electrolyte replacements in the form of athletic beverages restore electrolytes balances across cell membranes during exercise.
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