Proper Hydration for Exercise

Staying hydrated is essential for everyone, but athletes have an even greater need to maintain proper hydration. Water is the most important nutrient for life and has many important functions including regulating temperature, lubricating joints and transporting nutrients and waste throughout the body.

Hydration During Exercise
Staying hydrated is particularly important during exercise. Adequate fluid intake is essential to comfort, performance and safety. The longer and more intensely you exercise, the more important it is to drink the right kind of fluids.

Studies have found that athletes who lose as little as two percent of their body weight through sweating has a drop in blood volume which causes the heart to work harder to circulate blood. A drop in blood volume may also lead to muscle cramps, dizziness, fatigue and heat illness including: Inadequate fluid intake Excessive sweating Failure to replace fluid losses during and after exercise Exercising in dry, hot weather Drinking only when thirsty Because there is wide variability in sweat rates, losses and hydration levels of individuals, it is nearly impossible to provide specific recommendations or guidelines about the type or amount of fluids athletes should consume.

Finding the right amount of fluid to drink depends upon a variety of individual factors including the length and intensity of exercise and other individual differences. There are, however, two simple methods of estimating adequate hydration: Monitoring urine volume output and color. A large amount of light colored, diluted urine probably means you are hydrated; dark colored, concentrated urine probably means you are dehydrated. Weighing yourself before and after exercise. Any weight lost is likely from fluid, so try to drink enough to replenish those losses. Any weight gain could mean you are drinking more than you need. High altitude. Exercising at altitude increases your fluid losses and therefore increases you fluid needs. Temperature. Exercising in the heat increases you fluid losses through sweating and exercise in the cold can impair you ability to recognize fluid losses and increase fluid lost through respiration. In both cases it is important to hydrate. Sweating. Some athletes sweat more than others. If you sweat a lot you are at greater risk for dehydration. Again, weigh yourself before and after exercise to judge sweat loss. Exercise Duration and Intensity. Exercising for hours (endurance sports) means you need to drink more and more frequently to avoid dehydration.

To find the correct balance of fluids for exercise, the American College Of Sports Medicine suggests that "individuals should develop customized fluid replacement programs that prevent excessive (greater than 2 percent body weight reductions from baseline body weight) dehydration. The routine measurement of pre- and post-exercise body weights is useful for determining sweat rates and customized fluid replacement programs. Consumption of beverages containing electrolytes and carbohydrates can help sustain fluid-electrolyte balance and exercise performance."

According to the Institute of Medicine the need for carbohydrate and electrolytes replacement during exercise depends on exercise intensity, duration, weather and individual differences in sweat rates. [They write, "fluid replacement beverages might contain ~20–30 meqILj1 sodium (chloride as the anion), ~2–5 meqILj1 potassium and ~5–10% carbohydrate."] Sodium and potassium are to help replace sweat electrolyte losses, and sodium also helps to stimulate thirst. Carbohydrate provides energy for exercise over 60-90 minutes. This can also be provided through energy gels, bars, and other foods.

Sports drinks can be helpful to athletes who are exercising at a high intensity for 60 minutes or more. Fluids supplying 60 to 100 calories per 8 ounces helps to supply the needed calories required for continuous performance. It's really not necessary to replace losses of sodium, potassium and other electrolytes during exercise since you're unlikely to deplete your body's stores of these minerals during normal training. If, however, you find yourself exercising in extreme conditions over 3 or 5 hours (a marathon, Ironman or ultramarathon, for example) you may likely want to add a complex sports drink with electrolytes. While specific fluid recommendations aren't possible due to individual variability, most athletes can use the following guidelines as a starting point, and modify their fluid needs accordingly.

Hydration Before Exercise
Drink about 15-20 fl oz, 2-3 hours before exercise Drink 8-10 fl oz 10-15 min before exercise Hydration During Exercise
Drink 8-10 fl oz every 10-15 min during exercise If exercising longer than 90 minutes, drink 8-10 fl oz of a sports drink (with no more than 8 percent carbohydrate) every 15 - 30 minutes.

Hydration After Exercise
Weigh yourself before and after exercise and replace fluid losses. Drink 20-24 fl oz water for every 1 lb lost. Consume a 4:1 ratio of carbohydrate to protein within the 2 hours after exercise to replenish glycogen stores. Although rare, athletes can drink too much water and suffer from hyponatremia (water intoxication). Drinking excessive amounts of water can cause a low concentration of sodium in the blood - a serious medical emergency.

Sources

Consensus Statement of the 1st International Exercise-Associated Hyponatremia Consensus Development Conference, Cape Town, South Africa 2005. Clinical Journal of Sport Medicine. 15(4):208-213, July 2005.

Exercise and Fluid Replacement, ACSM Position Stand, American College Of Sports Medicine, Medicine and Science In Sports & Exercise, 2007.

Institute of Medicine. Water. In: Dietary Reference Intakes for Water, Sodium, Cholride, Potassium and Sulfate, Washington, D.C: National Academy Press, pp. 73–185, 2005.

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