How Much Water Should You Drink When You Exercise?

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My trainer is always telling me to stay hydrated. How much water should I drink when exercising? What will happen if I drink too much?

Doctor's response

The National Athletic Trainers' Association recommends the following hydration guidelines for exercise:

  1. Two to three hours pre-exercise: 17 to 20 fluid ounces of water or sports drink.
  2. Ten to 20 minutes pre-exercise: 7 to 10 ounces of water or sports drink.
  3. During exercise: Fluid replacement should approximate sweat and urine losses and at least maintain hydration at less than 2% body weight reduction. This generally requires 7 to 10 ounces of water or sports drink every 10 to 20 minutes. Include carbohydrates in the beverage if the exercise is intense or lasts more then 45-50 minutes. Water alone will suffice, and save calories, if the exercise is moderate or less than 45-50 minutes.
  4. Post-exercise: Athletes should weigh themselves nude before and after workouts to learn how much weight is lost from sweat (water and salt) and then ingest fluid equal to 150% of the weight loss, ideally within two hours, and no more than four to six hours after the event. Including sodium in the drink allows fluid volume to be better conserved and increases the drive to drink, and carbohydrate in the drink will improve the rate of intestinal absorption of the fluid as well as replenish glycogen stores in the muscles and liver.
  5. The volume of fluid in the stomach is critically important for proper hydration. Maintaining 12 to 20 ounces of fluid in the stomach will optimize gastric emptying and prevent dehydration. Concentrations of 4% to 8% of carbohydrates should be used if they are included in the fluid (for example, Gatorade and other energy drinks). Concentrations higher than 8% slow the rate of fluid absorption, while 6% to 8% concentrations are optimal for hydration and performance.

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Medically Reviewed by a Doctor on 8/7/2017

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