Knowing Your Sweat Rate Can Help You Stay Hydrated During Exercise

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January 25, 2013

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This post is available in: Spanish

The thousands of long-distance runners who have trained for months for this weekend’s ING marathon and half-marathon know how important hydration is for health and performance.

But with any type of exercise, it’s crucial to drink plenty of fluids to avoid dehydration.

It’s also important not to overdo it.

“Over-hydration is health a risk, too,” said Thomas San Giovanni, M.D. orthopedic surgeon at the Miami Orthopedics & Sports Medicine, and co-medical director of Miami Marathon. “So how do you know how much you need to consume?  Know your sweat rate.”

Your sweat rate will help you determine how much fluid you lose during exercise, and how many ounces you should drink, explains Dr. San Giovanni.

Here’s how to find your sweat rate:

  1. Before you exercise, weigh yourself without any clothes on.
  2. Perform your exercise activity (running, biking, swimming, etc.), making note of exactly how many fluids you consumed during activity, and exactly how long you exercised.
  3. Immediately after you exercise, weigh yourself without any clothes on.
  4. Calculate the difference between your pre-exercise weight and your post exercise weight in ounces. (Note: 1 lb = 16 oz)  Add to this number the ounces of fluids you drank.  Finally, divide by the duration of activity (in hours).

For example:
» Richard wants to find out his sweat rate when running.
» Weight before exercise = 150
» Weight after exercise = 149
» Fluids consumed during exercise = 20 oz
» Exercise duration = 2 hrs

» 150 lb – 149 lb = 1 lb (1lb = 16 oz)
» 16 oz  + 22 oz = 38 oz
» 38 oz ÷ 2 hrs = 19 oz
» Sweat rate = 19 oz per hour.

Richard loses 19 oz of fluids per hour when he runs. This means he will need to consume 19 oz of fluids to stay adequately hydrated.

Make sure to also take into consideration the climate during your exercise. Your sweat rate in the winter will be different from your sweat rate in the summer. As the weather changes, you’ll need to recalculate your rate.

Your sweat rate may not be the same for different types of activity. If you take part in different types of exercise, you should be aware of your sweat rate for each one.

“In addition to staying hydrated, make sure you stretch, eat well and use the appropriate equipment for your activity,” Dr. San Giovanni said. “Doing all of these will help you avoid injury and get better results out of your exercise.”

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