14 DAY TRIAL // For a long time, the United States military has been in doubt over how to most efficiently distribute water to its soldiers when they set out on two- or three-day missions. The solution they came up with in 1982 is called the Shapiro equation and has been used to this day to calculate just how much water a military man needs to carry so as to avoid dehydration. According to a new study, the old calculation vastly overestimates the amount of water needed. The paper also provides calculations that creators say are between 58 and 65 percent more efficient when it comes to the weight a soldier carries on missions.
The document, published in the latest issue of the respected Journal of Applied Physiology, argues that mission planners can safely use the new numbers in calculating water rationing, and gives several reasons why the Shapiro equation needs rethinking. Additionally, it argues that the old formulations need to be changed to take into account new clothing fabrics, expanded so as to predict water needs when working outdoors, and refined, in order to make the overall predictions more accurate, PhysOrg informs. The research also says that the revised form could be used to determine water needs for civilians working outdoors as well.
Water needs are largely calculated based on a person's body surface and on the amount of sweat they generate. Doctors explain that the harder the effort people make, the more oxygen their muscles consume. This leads to them overheating, and to sweat appearing so as to cool them down. When this happens, the overall volume of water in the body naturally decreases as well. But accurate predictions are difficult to make. In addition to each individual's body type, there are other factors to consider. For instance, while inactive people lose anywhere between one and three liters of water per day, those working actively or in intense heat can lose as much as six liters.
Naturally, these amounts of water need to be replaced, and a two-liter ration per day, as advocated by most health experts, seems like a poor way to do it. Moreover, exercise intensity, air temperature, clothing fabrics, humidity, genetic predispositions and wind patterns are all factors to be taken into account when estimating, for example, a soldier's water rations for three or more days. “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 write in the journal.