Most people lose as much as 1 qt (1 L) to 2 qt (2 L) of fluid during 1 hour of exercise. When you are not drinking enough fluids, your muscles get tired quickly, and you may have leg cramps while walking or running.

If you are an athlete, you can lose as much as 3 qt (3 L) of fluid per hour during an intense workout. Fluid loss in endurance activities such as distance running, cycling, strenuous hiking, or cross-country skiing can be severe. These types of activities can quickly lead to heat exhaustion.

In endurance athletes, dehydration can cause symptoms, called post-extreme endurance syndrome (PEES). Symptoms of PEES include decreased body temperature, nausea, vomiting, diarrhea, dizziness, headache, muscle cramps, and an inability to drink fluids.

Distance runners and other endurance athletes are not the only ones to have problems with dehydration. Football, basketball, and hockey players all may lose large amounts of fluid during a game. High school and college wrestlers often decrease their fluid intake and promote excessive sweating before a match in order to "make weight."

To protect yourself from dehydration:

• Drink 8 to 10 glasses of water every day.
• Drink extra water before, during, and after exercise.
• Take some water or a sports drink, such as Gatorade or Powerade, with you when you exercise and try to drink at least every 15 to 20 minutes. Use a sports drink if you will be exercising for longer than 1 hour.
• Avoid caffeinated drinks, such as coffee and colas, which increase urine output and make you dehydrate faster.
• Avoid alcoholic drinks, which increase dehydration and make it difficult to make good decisions.
• Do not take salt tablets. Most people get plenty of salt in their diets. If you are worried about replacing minerals lost through sweating, use a sports drink.
• Stop working outdoors or exercising if you become dizzy, lightheaded, or feel very tired.

It is important to protect yourself from dehydration in extremely hot or dry weather and at high elevations. Exercise early in the day or later in the evening when it is cooler.