A fluid loss of as little as 2 - 3 percent of body weight impairs performance. Fluid losses of 7 - 10 percent of body weight will lead to heat stroke and death. For a 150-pound person, a 2 - 3 percent fluid loss equates to 3 to 4 1/2 pounds of body weight.
Research shows that endurance athletes who are involved in physical activity for more than an hour and a half can produce up to three quarts of sweat per hour. That equals a loss of 6 pounds of body weight.
Fluid replacement is a special concern for children involved in sports. Children have lower sweating capacity and they tolerate temperature extremes less efficiently than adults. Young children also produce more heat during exercise. They typically take 2 to 3 days longer to acclimatize to exercise during warm weather. It is essential to keep the water bottle handy during all sports activities for children.
To best handle your fluid needs, the following simple rules can guide you as you exercise:
2. Plain water adequately replaces fluid for most athletes. Sports drinks or diluted juices that have less than 10 percent carbohydrate concentration may also be fluid replacers. On sports drink labels look for carbohydrate contents of less than 24 grams per 1 cup (8 oz). Dilute fruit juice by mixing one part juice with one part water. Extremely concentrated beverages such as carbonated sodas, undiluted fruit drinks and juices, and high carbohydrate supplements will slow absorption rates. They are not useful for immediate fluid replacement.
3. Don't depend on thirst. By the time you feel thirsty, your body has already started to dehydrate.
4. Weigh before and after an athletic event. Replace 2 cups of fluid for every 1 pound lost.
5. Sip water or dilute fluids (less than 24 grams of carbohydrate per cup) during competition or training. Athletes involved steadily in competition or training for longer than 90 minutes may benefit by using cool, pleasantly flavored and lightly sweetened beverages such as diluted fruit juices or sports drinks. These beverages provide both a fluid replacement and are a source of carbohydrate fuel.
The suggested protocol for fluid replacement is as follows:
Drink 2 1/2 cups fluid 1 to 2 hours before competition or training. Follow this by drinking about 1 1/4 cups fluid 15 minutes before the event.
Drink 3 to 6 oz (1/3 to 3/4 cup) every 10 to 15 minutes during competition or workout.
After competition or workout, weigh and replace every pound of lost weight with 2 cups fluid.
Table 1. Composition of selected commercial sport drinks
Product Carb Energy Sodium Potassium Carbohydrate
(8 oz) concentration
% kcal mg mg g
Bodyfuel 4.5 40 80 20 10
450a
Exceed Fluid 7.0 70 50 45 17
Replacementb
Gatoradec 6.0 50 110 25 14
Squincherd 6.8 60 55 45 16
aVitex Foods, Los Angeles, CA
bRoss Laboratories, Columbus, OH
cQuaker Oats Co., Chicago, IL
dUniversal Marketing Corp., Columbus, MO
Davis, J.M., Burgess, W.A., Slentz, C.A. and Bartoli, W.P. Fluid availability of sports drinks differing in carbohydrate type and concentration. Am. J. Clin. Nutr. 51:1054-1057, 1990.
Hoffman, C.J. and Coleman, E. An eating plan and update on recommended dietary practices for the endurance athlete. J. Am. Diet. Assoc. 91:325-330, 1991.
Houmard, J.A., Egan, P.C., Johns, R.A., Neufer, P.D., Chenier, T.C. and Israel, R.G. Gastric emptying during 1 h of cycling and running at 75% VO2max. Med. and Sci. in Sports and Exer. 23:320-325, 1991.
Marcus, J.B., ed. Sports Nutrition: A Guide for the Professional Working With Active People. Chicago, IL: American Dietetic Association (430 North Michigan Avenue). 1986.