A: Fluid balance or maintenance of normal hydration is critical for optimal exercise performance and overall health. A disturbance in fluid and electrolyte balance can affect cellular activities and the function of heart and muscles. For example, as little as a one percent reduction (e.g. 2 pounds in a 150 pounds person) in body weight due to dehydration can negatively affect the ability of the body to transfer heat and maintain normal temperature. Inability to regulate body temperature increases demands on the heart and impairs exercise-performance. Both high-intensity duration and moderate-low intensity endurance exercise-performance can be affected by fluid balance. For example, during one hour of exercise you can lose more than one quart of sweat, which is equivalent to 2.2 pounds if the fluid is not replaced. Additionally, the exercise intensity, duration of exercise, and the climate temperature can have dramatic influences on fluid balance.
Recommendations from The American College of Sports Medicine*:
- Before sports event make sure to drink adequate fluids and prior to the event or exercise.
- Drink about 500 ml (~2 cups) of fluid 2 h prior to exercise or event to promote adequate hydration and allow for time to relieve the body of excess water.
- During exercise start drinking early and continue drinking during the exercise or event at a rate that will replace lost fluids (i.e. sweating), or consume the maximal tolerated.
- Attempt to consume fluids with a temperature below ambient temperature (i.e. below 59-79∞F). Additionally, flavored beverages can be consumed to improve taste and increase likelihood of drinking.
- The addition of carbohydrate and/or electrolytes to fluid replacement solution is recommended for events greater than 1 h in duration since they may enhance performance.
- During exercise it is recommended to consume 30-60 g of carbohydrate every hour to maintain energy and delay fatigue. This can be achieved by consuming carbohydrate-containing fluids (600 to 1200 ml per hour) of solutions containing 4-8% carbohydrates as sugars (e.g. glucose or sucrose) or starch (e.g. maltodextran).
- Including sodium in drinking water (0.5-0.7 g/l) in fluid replacement beverage during exercise longer than 1 hour is recommended because it may improve palatability, promote fluid retention, and possibly prevent hyponatremia.
*Adapted from American College of Sports Medicine, Position Stand on Exercise and Fluid Replacement, Med. Sci. Sports Exerc., Vol. 28, No. 1, pp I-vii, 1996.
Web Resources:
Hydration Calculator: http://www.csgnetwork.com/hydratecalc.html
Sports Medicine: http://sportsmedicine.about.com/cs/hydration/
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