Calculating Sweat Rates
Why Calculate Sweat rates?
Sweat rates are highly variable between athletes and can also vary for any given individual (due to changes in conditions, such as ambient temperature and humidity). As a result it is impossible to predict the exact amount of fluid to replace during exercise.
However the following method will give you reasonably accurate data to then adopt a hydration plan that’s tailored to your body’s specific needs!
What Equipment Will I Need?
- Accurate weighing scales
- A dry towel
What Are The Steps?
Immediately before your exercise session weigh yourself naked (A).
Complete your session (keep a note of exercise duration) and record how much fluid was consumed during the session (B).
An easy way to measure this is to weigh your full bottle before and then after exercise, subtracting these values to record fluid consumption. *1 gram = 1 millilitre.
Immediately after exercise use the dry towel to wipe off any sweat from your skins surface before weighing yourself naked for a second time (C).
Subtract your post-exercise weight (C) from your pre-exercise weight (A) to calculate weight loss (X).
Your sweat rate can then be calculated using the following equation:
(X+B) / Exercise Duration
Working ExamplePre-exercise weight (A) – 75 kg
Post-exercise weight (C) – 5 kg
Fluid consumed during session (B) – 400ml or 400g
Exercise duration – 1 Hour
1. 75 kg (A) – 74.5 kg (C)
= Weight loss of 500g or 500ml (X)
2. (X+B) / Exercise Duration
So… (500g + 400ml) / 1 hour = 900ml per hour
Providing exercise conditions such as ambient temperature, humidity, and clothing are consistent to those of the test, you can then plan a hydration and fuelling strategy based on drinking 900ml per hour of exercise.
Whilst completing this test, we advise not to urinate between pre and post weight measurements, as this exact amount of extra fluid loss would not be taken into account. However if it does became unavoidable, you can use an estimate of 300ml fluid loss per urination. This will need to be subtracted from your estimated sweat rate.