How to Perform a Sweat Rate Test
Why Perform a Sweat Rate Test?
Everyone sweats differently. There is a huge between athlete variation in sweat lost per hour during exercise (sweat rate) and amounts of electrolytes lost per liter of sweat (sweat concentration). The American College of Sports Medicine position paper on electrolyte and fluid replacement shows sweat rates ranging from .5 liters per hour to 2.5 liters per hour across a wide range of sports. Other studies have shown that sweat sodium concentration ranges from 200mg per liter sweat lost to 2200mg per liter of sweat lost. A great first step to creating you individual hydration plan is to perform a sweat rate test. Here is how you do it.
Sweat Rate Testing Protocol
It is ideal to calculate sweat rate during a session that lasts 45 minutes to 2 hours. I you do a shorter test, this can be prone to errors in the equation, while anything longer can start to be skewed by things like fuel utilization (after two hours you begin to use larger amounts of glycogen, which can alter weight measurements), the need to urinate (preferably you don’t want to urinate during these tests) and food intake.
Items you will need
A scale
A calculator (fine to use your phone)
A dry towel
Whatever exercise equipment you require to do your sport (bike, running shoes, etc.)
Any fluid you need
Steps
1. Record the temperature outside or in the test room if possible as well as the location in which you are testing. Temperature and location inform the environmental conditions to which the test is applicable.
Temperature _______ Location _______ (record indoor or outdoor and actual physical location like Aspen or Charlotte)
2. Warm-up for approximately 10 minutes. By the end of the warm-up, you should be exercising at the exercise test intensity (your race pace if you are looking to apply the results on race day or your training pace if you are looking to apply the results to training days).
3. Urinate if you need to and then quickly towel dry and measure body weight in the nude (if possible).
Start body weight in pounds_____ kilograms _______
*To convert pounds to kilograms divide by 2.2 (130lb./2.2= 59.1kg) or use this calculator
4. Perform the exercise test (45 minutes to 1 hour is sufficient). The test should be done at the pace you are gathering data for (race pace or training pace).
Exercise Session Duration in minutes _______
5. Immediately dry yourself and take a post-exercise nude body weight.
End body weight in pounds_____ kilograms _______
*To convert pounds to kilograms divide by 2.2 (130lb./2.2= 59.1kg) or use this calculator
6. If you consumed fluid during the exercise session, record the amount of fluid you drank in ounces:
Ounces consumed______
7. It’s best to aim not to pee during these sessions as this can skew the results. However, if you do have to go, record number of pee breaks (it’s not a bad estimate to assume a fluid loss of ~0.3l (300ml) per bathroom stop).
# of pee breaks during the test_______
Calculating Sweat Rate
Now that you have your data, you can perform the following equations and/or plug your data into this excel spreadsheet:
A. Body Weight pre‐exercise _____ [lb/2.2 = kg]
B. Body Weight post‐exercise _____ [lb/2.2 = kg]
C. Change in Body Weight _____ grams [kg x 1000 = g]
(A-B)=C (be sure to convert kg to g as part of calculating C)
D. Volume of fluid consumed _____ mL [oz x 30 = mL]
E. Sweat Loss _____ mL [oz x 30 = mL]
(C + D)= E
F. Exercise time _____ [min or hr]
G. Sweat Rate _____ [mL/min or mL/hr]
(E/F)= G
To convert Sweat Rate (G) back into ounces: G/30 = oz
*Ideally, you should not have to pee during this test. However, if you do end up having to urinate, simply subtract 300mL for each bathroom stop from your final sweat rate number.
The final number (G) is your sweat rate, or the amount of fluid that you lose through sweat during a specific amount of exercise (usually expressed per 1-hour). This should help you determine the amount of fluid you should be drinking during and after your workouts.
A few important things to remember:
1) Sweat rate is effected by environmental factors such as heat, humidity, altitude, etc., so you will want to repeat this test in different conditions (winter vs. summer; hot vs. cold locations, etc.).
2) Sweat rates generally increase after 10-14 days of heat exposure, so sweat rate should be re‐calculated following heat acclimatization.