The goals of your nutrition strategy during practice, training, or competition are to consume enough carbohydrate (if necessary) to optimize performance and to consume an appropriate amount of fluid to maintain hydration. Research has shown almost unequivocally that consuming 30 to 75 grams of carbohydrate per hour during exercise will benefit performance during both prolonged and intermittent,high-intensity activities. Carbohydrate supplementation extends endurance and improves race time during simulated endurance races or trials and also improves sprinting ability and power output at the end of races or sporting events. Although less is known about team sports, a few relatively recent studies have found that carbohydrate intake during exercise improved tennis stroke quality during the final stages of prolonged play and physical and mental function during intermittent shuttle running that mimicked that of many competitive team sports. 

Carbohydrate ingestion most likely exerts these performance benefits by maintaining blood glucose concentration, thereby ensuring a continuous source of carbohydrate for the working muscle. These benefits are most noted during the latter stages of a race or after half-time when the liver and muscle glycogen are compromised, and—with prolonged events—are in addition to those gained by consumption of a pre-exercise carbohydrate meal. Fluid intake, with or without carbohydrate, also ensures optimal performance. Research in this area has shown—without a doubt—that fluid ingestion during exercise improves endurance performance and that the performance-enhancing effects of carbohydrate and fluid are independent but additive. 

For example, one study conducted in the late 1990s at the Chichester Institute of Higher Education in the United Kingdom found that male and female runners were able to run 33 percent longer before exhaustion when they consumed 180 milliliters (0.75 cups)of water every 15 minutes compared to when they consumed no fluids. Their actual time to exhaustion during the treadmill test was 133 minutes when they consumed water and 78 minutes when they did not. Another study conducted at the University of Texas in Austin found that male athletes experienced a 6 percent improvement in sprinting performance when they consumed 1,330 milliliters(5.6 cups) of water, enough to replace about 80 percent of their fluid lost through sweat, compared to when they ingested just 200 milliliters (0.85 cups) of water.

In this study, the athletes cycled for 50 minutes at a relatively intense effort before completing a sprint to the finish that took approximately 10 minutes. Not surprisingly, the athletes experienced a 12 percent improvement in performance when they consumed 1,330 milliliters of carbohydrate-containing sports drink rather than water. Although dehydration from inadequate fluid consumption can impair the performance, both dehydration and overhydration can result in severe, life-threatening health consequences that are worth mentioning here. Briefly, varying degrees of dehydration are common during exercise because athletes typically drink enough to satisfy their thirst but do not drink enough to offset the fluid losses that occur during sweating. 

This is primarily because thirst is not an adequate guide to fluid replacement, but it is also caused by factors such as water availability; game rules and regulations; an intense focus on playing, training, or racing; and even drinking skill during exercise. Dehydration can lead to increased core temperature, headache, dizziness, gastrointestinal discomfort, poor concentration, and reduced performance. All of these symptoms are a result of decreased blood flow, which reduces the escape of heat through the skin and the absorption of ingested fluid and foods. 

If not corrected, dehydration can lead to heat injury, exhaustion, heatstroke, and death.In contrast, hyponatremia, or “water intoxication,” has emerged as a cause of life-threatening illness and race-related death in endurance competitions such as the marathon and ultramarathon. Hyponatremia occurs when excess water, relative to sodium, accumulates in the blood and is defined by an abnormally low concentration of plasma sodium (less than 135 mmol/l). In athletes, it is called water intoxication because it seems to result from drinking an excessive amount of low-sodium fluids during prolonged endurance exercise. 

A recent report found that hyponatremia occurred in approximately 13 percent of runners completing the 2002 Boston Marathon, and of those 13 percent, slightly less than 1 percent experienced severe hyponatremia (sodium concentration less than 120 mmol/l).1 In this event, the strongest indication of hyponatremia was weight gain during the race of one kilogram to almost five kilograms (2.2-11 lbs)caused by fluid intake that far exceeded the sweat rate. This and other studies also seem to indicate that those at greatest risk for hyponatremia are female and slower athletes who finish toward the back of the pack, although hyponatremia does occur in male athletes and appears to increase with the use of nonsteroidal anti-inflammatory drugs during competition. 

To avoid becoming hyponatremic, athletes should know their approximate sweat rate during all sports in which they participate and drink only enough to replace your losses. Drinking sodium-containing fluids such as higher-sodium fluid-replacement beverages or ingesting sodium-containing foods during events lasting more than two hours Pooya Ketab may also be prudent. Unfortunately, general symptoms of hyponatremia are nonspecific and include fatigue, nausea, and confusion. Severe cases can result in grand mal seizures, respiratory arrest, acute respiratory distress syndrome, coma, and death.

In addition to carbohydrate and fluid, several recent studies have also suggested that protein consumed along with carbohydrate and fluid may enhance aerobic endurance, reduce muscle damage, and improve fluid retention above that which occurs with carbohydrate alone or carbohydrate plus fluid. The specific mechanisms for this effect of protein (given in a ratio of 4 grams carbohydrate to 1 gram protein) are not yet well understood and as such should be considered preliminary. In these studies, for example, the researchers tested aerobic endurance by having athletes exercise to exhaustion but did not determine if they would run or cycle faster with the protein-containing carbohydrate beverage compared to just the carbohydrate-containing beverage.