Physiology and Performance Benefits of Optimal Hydration

Ellen Coleman, M.P.H., M.A., R.D., Private Practice

Athletes should closely match their fluid intake with their fluid loss from sweating to prevent dehydration.
Weight before and after training and simulated competitive conditions to determine amount of fluid lost per hour.
Follow a fluid replacement schedule that is based on the hourly amount of fluid lost during exercise.
A one lb weight loss is equivalent to 16 oz (480 mL) of fluid.
For a two lb weight loss per hour, the athlete should drink 8 oz (240 mL) of fluid every 15 minute or 1/2 of a 16 oz water bottle.
Consuming adequate fluids during training enables the athlete to maintain a desirable exercise intensity, allows the athlete to practice proper hydration techniques for competition, and protects against heat illness.
Two hours before exercise, the athlete should hyperhydrate by drinking 17 oz (500 mL) of fluid.
During exercise, the athlete should drink at least 5 - 10 oz (150 - 300 mL) of fluid every 15 - 20 minutes to replace sweat losses. This equals 20 - 40 oz (600 - 1,200 mL) per hour.
The actual amount of fluid consumed during exercise will depend on the athlete's rate of fluid loss from sweating. Inadequate fluid intake is the primary obstacle to fluid replacement.
Thirst is not an adequate guide, since athletes only replace about 50% of their fluid losses during exercise.
Fluid intake must be regulated by drinking according to a schedule, rather than in response to thirst.
Fluid containers must be readily accessible (i.e. personal water bottle or team fluid coolers).
Following exercise, the athlete should drink 17 oz (500 mL) for every pound lost. Avoid beverages containing alcohol and caffeine following exercise.
Urine that is of small volume, dark yellow in color, and has a strong odor may indicate a dehydrated state. (Vitamins can also darken urine)
Enhancing the palatability of the fluid replacement beverage improves the match between fluid intake and sweat losses.
Fluids that are flavored, sweetened, and cooled increase voluntary fluid intake.
The ideal fluid replacement beverage tastes good, promotes rapid absorption, provides energy, and provides electrolytes.
The carbohydrate in sports drinks maintains blood glucose concentration, enhances carbohydrate oxidation, and improves performance.
Fluid replacement and carbohydrate ingestion independently improve high intensity exercise lasting an hour (i.e. a racquetball match). These beneficial effects are additive.
Consume 30 - 60 grams of carbohydrate per hour. Drinking 20 oz (600 mL) each hour of a sports drink which contains 6% carbohydrate (Gatorade) provides 35 grams of carbohydrate.
Sports drinks should provide glucose, sucrose, or maltodextrin as their major carbohydrate source. Fructose should not be the predominant sugar.
Multiple sugars enhance fluid absorption. Carbohydrate concentrations less than 8% (fewer than 19 g of carbohydrate per 8 oz) appear to maximize fluid absorption.
Sodium in sports drinks maintains fluid balance, replaces electrolytes lost in sweat, enhances drink to drink, and enhances palatability.

References

American College of Sports Medicine (1996) Position stand: exercise and fluid replacement. Med Sci Sports Exerc. 28:i-vii

Below, P.R., R. Mora-Rodriguez, J. Gonzalez-Alonzo, and E.F. Coyle. (1995). Fluid and carbohydrate ingestion independently improve performance during 1 hr of intense exercise. Med Sci Sports Exerc. 27:200-210

Coyle, E.F., and S.J. Mountain (1992). Benefits of fluid replacement with carbohydrate during exercise. Med Sci Sports Exerc. 24(suppl):S324-S30

Murray, R. (1998). Fluid needs of athletes. In: J.R. Berning and S.N. Steen (eds) Nutrition for Sport & Exercise. 2nd ed., Gaithersberg, MD: Aspen Publishers.

Physiology and Performance Benefits of Optimal Hydration

Athletes should closely match their fluid intake with their fluid loss from sweating to prevent dehydration.

Weight before and after training and simulated competitive conditions to determine amount of fluid lost per hour.

Follow a fluid replacement schedule that is based on the hourly amount of fluid lost during exercise.

A one lb weight loss is equivalent to 16 oz (480 mL) of fluid.

For a two lb weight loss per hour, the athlete should drink 8 oz (240 mL) of fluid every 15 minute or 1/2 of a 16 oz water bottle.

Consuming adequate fluids during training enables the athlete to maintain a desirable exercise intensity, allows the athlete to practice proper hydration techniques for competition, and protects against heat illness.

Two hours before exercise, the athlete should hyperhydrate by drinking 17 oz (500 mL) of fluid.

During exercise, the athlete should drink at least 5 - 10 oz (150 - 300 mL) of fluid every 15 - 20 minutes to replace sweat losses. This equals 20 - 40 oz (600 - 1,200 mL) per hour.

The actual amount of fluid consumed during exercise will depend on the athlete's rate of fluid loss from sweating. Inadequate fluid intake is the primary obstacle to fluid replacement.

Thirst is not an adequate guide, since athletes only replace about 50% of their fluid losses during exercise.

Fluid intake must be regulated by drinking according to a schedule, rather than in response to thirst.

Fluid containers must be readily accessible (i.e. personal water bottle or team fluid coolers).

Following exercise, the athlete should drink 17 oz (500 mL) for every pound lost. Avoid beverages containing alcohol and caffeine following exercise.

Urine that is of small volume, dark yellow in color, and has a strong odor may indicate a dehydrated state. (Vitamins can also darken urine)

Enhancing the palatability of the fluid replacement beverage improves the match between fluid intake and sweat losses.

Fluids that are flavored, sweetened, and cooled increase voluntary fluid intake.

The ideal fluid replacement beverage tastes good, promotes rapid absorption, provides energy, and provides electrolytes.

The carbohydrate in sports drinks maintains blood glucose concentration, enhances carbohydrate oxidation, and improves performance.

Fluid replacement and carbohydrate ingestion independently improve high intensity exercise lasting an hour (i.e. a racquetball match). These beneficial effects are additive.

Consume 30 - 60 grams of carbohydrate per hour. Drinking 20 oz (600 mL) each hour of a sports drink which contains 6% carbohydrate (Gatorade) provides 35 grams of carbohydrate.

Sports drinks should provide glucose, sucrose, or maltodextrin as their major carbohydrate source. Fructose should not be the predominant sugar.

Multiple sugars enhance fluid absorption. Carbohydrate concentrations less than 8% (fewer than 19 g of carbohydrate per 8 oz) appear to maximize fluid absorption.

Sodium in sports drinks maintains fluid balance, replaces electrolytes lost in sweat, enhances drink to drink, and enhances palatability.

References

American College of Sports Medicine (1996) Position stand: exercise and fluid replacement. Med Sci Sports Exerc. 28:i-vii

Below, P.R., R. Mora-Rodriguez, J. Gonzalez-Alonzo, and E.F. Coyle. (1995). Fluid and carbohydrate ingestion independently improve performance during 1 hr of intense exercise. Med Sci Sports Exerc. 27:200-210

Coyle, E.F., and S.J. Mountain (1992). Benefits of fluid replacement with carbohydrate during exercise. Med Sci Sports Exerc. 24(suppl):S324-S30

Murray, R. (1998). Fluid needs of athletes. In: J.R. Berning and S.N. Steen (eds) Nutrition for Sport & Exercise. 2nd ed., Gaithersberg, MD: Aspen Publishers.