Jun 22, 2017
Understanding Sweat Rate
Linda Samuels

Summer is here! Before athletes kick off any long workouts in the sun, make sure they’re familiar with their sweat rate and have a personal hydration plan. Here’s how to calculate sweat rate:

Step 1: Have athletes record their weight just prior to exercise (have them urinate prior to this weigh-in).

(Have the athlete make note if they urinate during exercise session.)

Step 2: Record athletes’ weight just after exercise (have them urinate prior to this weigh-in).

Step 3: Subtract weight from Step 2 from Step 1 for weight loss.

Step 4: Convert to ounces by multiplying by 16.

Step 5: Add the ounces of fluids the athlete drank during exercise to weight loss ounces. This equals their total weight loss.

Step 6: Divide total weight loss by the number of hours they exercised = sweat rate.

Note: If you find that an athlete loses more than 2 percent of their bodyweight during the sweat rate test (taken during a typical exercise session), or if they are a “salty sweater,” it is recommended that they work with a sports dietitian.

Example: Athlete A

Weight prior to exercise = 160 pounds

Weight after exercise = 158 pounds

Convert the difference to ounces = 2 pounds x 16 ounces = 32 ounces of weight loss

Add ounces of fluid drank = 12 ounces

Divide by hours exercised = 44 ounces ÷ 2 hrs

Athlete A’s sweat rate is 22 ounces per hour. Then, divide this number into the number of hydration opportunities during each hour to come up with a personal hydration plan. For example, if the athlete can drink every 10 minutes each hour of exercise, you would divide the 22 ounces by 6 for a drinking plan of approximately 3 to 4 ounces per 10 minutes. If the athlete can only drink every 15 minutes, you would divide 22 by 4 for a drinking plan of approximately 5 to 6 ounces per 15 minutes.

One important reminder: Personal hydration plans can change if the weather or intensity of exercise is different from conditions during the sweat rate test. You need to know athletes’ sweat rate for many different weather conditions/intensities. Log their sweat rates/conditions so you can easily reference your data.

Here’s a handout to walk you through how to find athletes’ sweat rates.

Weight prior to exercise _____________

Weight after exercise (subtract) – _____________

Convert to ounces _____________ (pounds x 16 ounces = ounces of weight loss)

Add ounces of fluid drank +_____________ (total ounces of weight loss)

Divide by hours exercised =______÷_______ = sweat rate per hour

Temperature/humidity _____________

Describe training session/intensity __________________________________________________

Image by Keith Allison

Linda Samuels, MS, RD, CSSD, LDN, is the owner of Training Table Sports Nutrition, LLC, a private nutrition consulting practice in Chicago that specializes in working with endurance athletes, particularly triathletes. She also is the Team Dietitian for the Northwestern University triathlon club team and works with professional boxers. Samuels can be reached at: [email protected].

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