The Shapiro equation needed to be:

• updated, to take into account new fabric in the clothing soldiers wear
• expanded, to predict water needs over long hours working outdoors
• refined, to make the predictions more accurate

In this study, the researchers collected data on 80 men and 21 women who exercised in the laboratory under varying conditions of work intensity and duration, environmental conditions such as temperature and humidity, and types of clothing. They measured the sweat losses for each volunteer and compared that to the sweat loss predicted by the equation. Once they were able to compare the prediction versus the real sweat rate, they derived specific algorithms statistically so that the predictions would more accurately reflect the observed sweat rates.

The study produced two equations. The researchers then cross validated the new equations, using new data from 21 men and 9 women. One of the equations increased the prediction accuracy by 58% and one increased accuracy by 65%. Either of these equations would provide predictions accurate enough to be used in the field, Dr. Cheuvront said.

"The new equations provide for more accurate sweat predictions over a broader range of conditions with applications to public heath, military, occupational and sports medicine settings," the authors wrote. The equation can be used in temperatures of 70-125 F, the same temperature range as the old equation, but now can predict sweat loss for up to eight hours of work, as opposed to two hours for the old formula.

As it stands, the equation would be difficult for members of the public to use. It contains many variables, reflecting the complexity of predicting sweat loss, such a
'/>"/>