hiker staying hydrated

Exercise raises our body temperature depending on the intensity and duration of the workout. To regulate our temperature and keep from getting too hot while exercising or playing sports, we produce sweat that’s composed of water and electrolytes.

Sweat is the primary way we cool down, but this can also lead to a substantial loss of water and electrolytes leading to dehydration and possibly heat illness.

Know the Signs: Dehydration Symptoms

Mild Dehydration

  • Dry sticky mouth
  • Dry skin
  • Headache
  • Muscle fatigue
  • Decreased performance
  • Increased urine concentration (appears darker yellow)
  • Constipation

These symptoms are non-specific and can also be caused by heat illness, including cramps, heat exhaustion and heat stroke.

Severe Dehydration

  • Extreme thirst
  • Heat illness
  • Mental fogginess
  • Irritability
  • Confusion

Individuals showing signs of severe dehydration or heat illness should be cooled down immediately by transferring to a cool location and possibly placing the individual in an ice immersion bath. (Medical personnel should be contacted immediately if showing any confusion or mental fogginess.)

Hydration Strategies to Prevent Dehydration

  1. Don't go by thirst alone.

    Thirst is not the sole indicator of hydration status and should not be used to monitor hydration.

  2. Weigh yourself before and after exercise.

    This is a more exact method to monitor sweat loss and fluid needs (see guidelines below). This can be helpful you have multiple workouts in a row (i.e. fall sports practices).

    • Well hydrated: +/- 1% of body weight
    • Minimal dehydration: - 1 to 3 %
    • Significant dehydration: - 3 to 5%
    • Serious dehydration: - 5%
  3. Prepare by taking it slow.

    If you’re new to exercising in heat, it takes two weeks for your body to adjust and regulate use of water.

    • Increase your workout intensity and duration slowly while acclimating.
    • Exercise in cool areas or earlier in the day.
    • Stay motivated. Dehydration is the number one cause of mild and serious heat related illness.
  4. Rethink your drinks.

    You only need water if you are exercising for less than an hour. When choosing a sports drink for a workout longer than an hour, look for 4-8 percent carbohydrate concentration, 20-30 meg/L of sodium and to 2-5 meg/L of potassium.

Listen to Dr. Jeremy Johnson discuss keys to hydration.

Hydration Before, During and After Workouts

Before Exercise

In hot conditions, drink 16-20 ounces of water four hours before your workout; consider an additional 8-12 ounces of water 15 minutes before your workout if you are sweating a lot or it is extremely hot.

During exercise

For workouts lasting less than one hour: Drink 3-8 ounces of water every 15-20 minutes, or 16-32 ounces after the workout.

For workouts greater than one hour: Drink 3 to 8 ounces of a sports beverage, every 15-20 minutes.

For all workouts, avoid over-hydrating. “Water intoxication” can be very dangerous, even deadly. Symptoms are similar to dehydration and heat illness. To avoid over-hydration, DO NOT drink more than 1 liter (33 ounces) of water per hour.

After Exercise

Check your body weight. Aim to correct losses within two hours after exercise. Drink 20-24 ounces of water for every pound lost.


June 17, 2019 | by Jeremy D. Johnson MD, MPH, RMSK