What to Drink for Proper Hydration During Exercise

Side view of woman drinking water

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Staying hydrated is essential for everyone, but athletes have an even greater need to drink and replace fluids during exercise. Water is the most important nutrient for life and has many important functions including regulating temperature, lubricating joints and transporting nutrients throughout the body while removing waste and toxins from the body.

Hydration During Exercise

Proper hydration throughout the whole day is essential for peek performance even before exercising. Staying hydrated is also particularly important during exercise. Adequate fluid intake is essential to comfort, performance, and safety. The longer and more intensely you exercise, the more important it is to drink the right amount of fluids, along with consuming carbohydrates and minerals like potassium, magnesium, and sodium.

Dehydration Decreases Performance

Studies have found that athletes who lose as little as two percent of their body weight through sweating have a drop in blood volume which causes the heart to work harder to circulate blood. A drop in blood volume may also lead to muscle cramps, dizziness, fatigue, and heat illness including:

Common causes of dehydration:

  • Inadequate fluid intake (especially before starting exercise and/or not replenishing enough fluids post-exercise)
  • Excessive sweating
  • Failure to replace fluid losses during and after exercise
  • Exercising in dry, hot weather
  • Drinking only when thirsty

What Should Athletes Drink?

At baseline, the average amount of fluids lost during exercise for an hour is about 0.5 to 2 liters of fluid or about 2–4 cups of fluid. This comes out to about 12-16 ounces every 5-15 minutes of exercise with performance decreasing after 60–90 minutes without replenishing fluids, carbohydrates, and electrolytes. The wide variability is related to sweat rates, losses and hydration levels of individuals, intensity of the exercise, length of exercise, humidity, heat, and elevation.

There are, however, two more individualized methods to estimate adequate hydration:

  1. Monitoring urine volume output and color. A large amount of light-colored, diluted urine probably means you are hydrated; dark colored, concentrated urine probably means you are dehydrated.
  2. Weighing yourself before and after exercise. Any weight lost is likely from fluid, so try to drink enough to replenish those losses. For every pound lost, drink about 3 cups of water.

How Athletes Lose Water

  • High altitude. Exercising at altitude increases your fluid losses and therefore increases your fluid needs.
  • Temperature. Exercising in the heat increases your fluid losses through sweating and exercise in the cold can impair your ability to recognize fluid losses and increase fluid lost through respiration. In both cases, it is important to hydrate.
  • Sweating. Some athletes sweat more than others. If you sweat a lot you are at greater risk for dehydration. Again, weigh yourself before and after exercise to judge sweat loss. Remember, about 3 cups of fluids for every pound loss during exercise.
  • Exercise Duration and Intensity. Exercising for hours (endurance sports) means you need to drink more and more frequently to avoid dehydration.

To find the correct balance of fluids for exercise, the American College Of Sports Medicine suggests that "individuals should develop customized fluid replacement programs that prevent excessive (greater than 2 percent body weight reductions from baseline body weight) dehydration. The routine measurement of pre- and post-exercise body weights is useful for determining sweat rates and customized fluid replacement programs. Consumption of beverages containing electrolytes and carbohydrates can help sustain fluid-electrolyte balance and exercise performance."

According to the Institute of Medicine, the need for carbohydrate and electrolytes replacement during exercise depends on exercise intensity, duration, weather, and individual differences in sweat rates.

They write, "fluid replacement beverages might contain ~20–30 meqILj1 sodium (chloride as the anion), ~2–5 meqILj1 potassium and ~5–10% carbohydrate." Sodium and potassium are to help replace sweat electrolyte losses, and sodium also helps to stimulate thirst. Carbohydrate provides energy for exercise over 60-90 minutes. This can also be provided through energy gels, bars, and other foods.

What About Sports Drinks?

Sports drinks can be helpful to athletes who are exercising at a high intensity for 60 minutes or more. If you find yourself exercising in extreme conditions over 3 or 5 hours (a marathon, Ironman or ultramarathon, for example) you may likely want to add a complex sports drink with electrolytes, including magnesium as this is lost through sweat as well.

Fluids supplying 30-60 grams of carbohydrates per hour are needed for continuous performance beyond 60-90 minutes.

General Guidelines for Fluid Needs

While specific fluid recommendations aren't possible due to individual variability, most athletes can use the following guidelines as a starting point and modify their fluid needs accordingly.

Hydration Before Exercise

  • Drink about 2.5 cups of fluids or sports drink before bed
  • Drink about 2.5 cups of fluids upon waking up
  • Drink another 1.5-2.5 cups of fluids 20-30 minutes before exercising

Hydration During Exercise

  • Drink 12-16 fluid ounces every 5-15 minutes
  • If exercising longer than 90 minutes, drink 12-16 fluid ounces every 5-15 minutes of a solution containing 30-60 grams of carbohydrates (or 6%–8% carbohydrate solution), sodium (300-600 mg per hour), potassium, and magnesium.

Hydration After Exercise

  • Weigh yourself before and after exercise and replace fluid losses.
  • Drink 24 fl oz or about 3 cups of water for every 1 lb lost.
  • Consume a 4:1 ratio of carbohydrate to protein close to the time when the exercise ends.

Drinking too Much Water

Although rare, athletes can drink too much water and suffer from hyponatremia (water intoxication). Drinking excessive amounts of water can cause a low concentration of sodium in the blood—a serious medical emergency.

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Article Sources
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  1. Kerksick, C.M., Wilborn, C.D., Roberts, M.D. et al. ISSN exercise & sports nutrition review update: research & recommendationsJ Int Soc Sports Nutr 15, 38 (2018). doi:10.1186/s12970-018-0242-y

Additional Reading
  • Consensus Statement of the 1st International Exercise-Associated Hyponatremia Consensus Development Conference, Cape Town, South Africa 2005. Clinical Journal of Sport Medicine. 15(4):208-213, July 2005.

  • Institute of Medicine. Water. In: Dietary Reference Intakes for Water, Sodium, Cholride, Potassium and Sulfate, Washington, D.C: National Academy Press, pp. 73–185, 2005.

  • Exercise and Fluid Replacement, ACSM Position Stand, American College Of Sports Medicine, Medicine and Science In Sports & Exercise, 2007.