Hydration for Peak Performance
BY BARBARA A. BREHM, ED.D.
PHYSICAL ACTIVITY INCREASES your fluid needs in several ways. You sweat during exercise to get rid of excess heat. You also lose water when you breathe, especially when the air is dry, since you humidify the air in your lungs. Cold air holds little moisture, and you can lose more than 1 liter of fluid when you exercise for several hours in the winter.
In cold air or water, your blood huddles into your core to prevent heat loss. But this change in core blood volume stimulates the kidneys to make urine, another form of fluid loss. As you warm up and circulation expands back into the skin, this water needs to be replaced for optimal performance.
It's easy to keep up with your increased fluid needs if you keep an eye on your water intake. While thirst tells you it's time to drink, athletes need to drink before the thirst mechanism is activated in order to keep up with rapid fluid losses during exercise, especially when exercise is vigorous and lasts for more than 30 minutes. Here are some guidelines to help you be sure you are getting enough to drink:
Weigh yourself before and after physical activity. Weight loss is a good indicator of dehydration. Each pound of lost weight means you should drink another 2 cups of fluids before and during exercise. If you weigh yourself before and after exercise, you can calculate your water deficit.
Check the color of your urine throughout the day. Urine should be pale in color. Dark, concentrated urine indicates dehydration. Some vitamin supplements cause deep yellow urine. If this is your case, then monitor urine volume, which should be plentiful.
Practice drinking adequate fluids during training. Learning how to stay hydrated is especially important if you are training for an event requiring prolonged, vigorous activity, such as a marathon or triathlon. Part of your training is to figure out how much water you typically lose for a given period of time under standard conditions (whatever they are for your area), and then practice staying hydrated.
If you will be consuming sports drinks, figure out which sports drinks work best for you during your training workouts, not on race day! Some people find certain drinks, especially those containing fructose, cause abdominal cramps or diarrhea when consumed during vigorous exercise.
Drink plenty of water before an important competition. You are limited in how much water you can absorb during exercise, so it is possible to lose water more quickly than you can replace it. Therefore, it is important to begin your long workout or contest well hydrated. Drink plenty of fluids during the 24 hours preceding your event. Then drink 2 or 3 cups of water or a sports drink two or three hours before the event. Finally, drink another cup 10 or 20 minutes before the race begins.
Drink during exercise. Optimal water intake during a contest varies widely, but sports nutritionists generally recommend about 1 cup every 15 minutes -- more if you are larger or a heavy sweater. Water is fine for shorter (less than one hour) events. If you will be exercising longer, a sports drink might be helpful to keep your blood sugar levels up and replace electrolytes (especially sodium and potassium) lost in sweat.
But don't drink too much. Sodium levels in the blood can dip too low when sodium losses through sweating are combined with excessive water intake. Most cases occur in slow, inexperienced marathoners (more than four hours) who exercise at lower intensities and drink too much water.
Drink after exercise. If your workout or event was quite long, you may not have been able to drink enough to keep up with fluid losses. Drink 2 cups of fluids for every 1 pound of weight lost. Sports drinks are especially helpful if you are dehydrated. Consuming fluids with carbohydrate soon after exercise will help your body replenish glycogen stores. FM
Barbara A. Brehm, Ed.D., is professor of exercise and sport studies at Smith College, Northampton, Mass.