Cheuvront et al developed field equations for estimating sweat loss in women runners. The authors are from the U.S. Army Research Institute of Environmental Medicine and Florida State University.


The full equation for estimating sweat loss is:


total sweat loss in kilograms =

= (change in body weight in kilograms) + (fluid intake in kilograms) + (trapped sweat in clothing in kilograms) – (urine loss in kilograms) – (respiratory water loss in kilograms) – (metabolic mass loss in kilograms)


change in body weight in kilograms =

= (weight before running in kilograms) – (weight after running in kilograms)


trapped sweat in clothing in kilograms =

= (weight of clothes after running in kilograms) – (weight of clothes before running in kilograms)


respiratory water loss =

= (0.019 * (oxygen uptake in liters per minute) * (44 – (ambient water vapor pressure in mm Hg)) * (run time in minutes))



• Including trapped sweat in clothing strikes me as if this amount was being counted twice.

• The equation for metabolic mass loss was hard to decipher (see page 1346). This only amounted to 0.1 kilograms.

• The units for sweat loss was in kilograms, but the authors also referred to loss in liters per hour. The conversion requires knowing the density of the sweat, with liters = (kilograms sweat) / (density). According to the Geigy Scientific Tables, sweat has a specific gravity from 1.001 to 1.008. To keep things simple I left this isodense with water.


To simplify this for field use, the following equation (formula F-3) can be used:


field estimate total sweat loss in kilograms =

= (change in body weight in kilograms) + (fluid intake in liters) – (urine loss in liters)



• The equation tended to overestimate sweat loss by about 0.2% in warm weather and by about 14.1% in cool weather.

• If the urine was not measured, the equation overestimated sweat loss by 6.4% in warm weather and 31.2% in cold weather.


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