An Athlete's Guide to Late-Summer Dehydration

Learn how to avoid hitting the wall this summer with hydration tips from STACK Expert Amy Rizzotto.

Summer dehydration

With the summer heat bearing down, athletes should be especially mindful of proper hydration. During strenuous exercise in extreme heat, your body can lose up to two liters of fluid every 30 minutes, and you need to drink two to four glasses of water for each hour of physical activity.

This shouldn't be surprising when you consider that on average, a man's body weight is 60 percent water, and a woman's approximately 50 percent. Since muscle contains more water than fat does, the percentage can be as low as 40 in an overweight person and 70 in a muscular person.

Nothing affects endurance, strength and performance more than dehydration. It can decrease your cardiovascular system function and aerobic power and throw off your body's ability to regulate its temperature. It can also contribute to gastrointestinal discomfort and overall fatigue, making it nearly impossible to be at the top of your game.

Dizziness, headaches, profuse sweating, nausea, weakness and visual disturbances may indicate the onset of heat exhaustion from dehydration. Drinking water and electrolytes at the first sign of these symptoms may help you avoid painful cramps. Ignoring the symptoms, on the other hand, could put you in serious trouble with heat stroke, possibly leading to seizures and even death.

According to a study published in June 2013 by the Centers for Disease Control and Prevention (CDC), extreme heat contributes to more 650 deaths each year. From 1999 to 2009, 7,233 people in the United States died from heat-related conditions.

For prolonged physical activities like marathons, triathlons and tournaments, athletes absolutely need to replace fluids. After 60 minutes of strenuous exertion, you should also replenish energy-stoking glucose stores along with the salt that you lose when you sweat. Sports drinks with added electrolytes may be helpful.

Most sports drinks on the market today—think Gatorade—typically contain 14 to 18 grams of carbohydrates in the form of glucose per 8-ounce serving, as well as a blend of muscle-friendly electrolytes like sodium and potassium. One 24-ounce bottle can give your body all it needs to replenish itself after an hour of intense training in high temperatures.

Active women should drink at least two liters of water every day, and men should drink three liters. If you're working out for more than an hour in the heat, add sports drinks to your fluids, too.

How to Prevent Summer Dehydration

Here are guidelines for athletes to avoid dehydration-related "bonking" (hitting the wall), as well as more serious heat-related illness:

  • Drink three 8-ounce servings of water for every pound of body weight you lose during activity.
  • Check urine color—the clearer the better!
  • Chug as much water as possible 24 hours before competition (hyperhydration).
  • Two to three hours before an event, drink 1-1/2 to 2-1/2 cups of water.
  • For events lasting longer than 30 minutes, consume 1/2 cup to 1-1/2 cups of water every 15 minutes.
  • Make sure you're losing no more than 2% of your body weight during competition (a 150-pound runner can lose up to 3% of her body weight in an hour without proper hydration).
Read more:


Williams, Melvin H. Nutrition for Health, Fitness and Sport: 8th Edition. McGraw-Hill. May 2006.

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