Water needs difficult to predict
The Army spends substantial resources transporting water to troops in the field, including Afghanistan and Iraq. Water transport accounts for about one-third of in-theatre costs, according to Dr. Cheuvront. The Institute of Medicine has also expressed interest in improving the prediction of water needs for the general public and disaster relief efforts. Dr. Cheuvront points out that an improved sweating prediction equation would not only help keep troops healthy and cut the cost of operations, but would also facilitate better civilian water planning when desired.
The harder an individual exercises, the more oxygen he or she consumes and the more heat the body produces. Sweat is the body's coolant, but it only cools when it evaporates from the skin. When it is muggy out, the air is moist, slowing the sweat evaporation rate and reducing its cooling power.
Sweat rate and water needs are difficult to predict because water needs are so variable. Inactive individuals lose between one and three liters of body water a day. More activity and warmer climates can double or even triple ordinary losses. Sweat rates also vary depending on body size, exercise intensity, clothing, air temperature, humidity, wind, and even the individual's own genes.
The Shapiro equation, developed more than 25 years ago, is expressed as (msw (gm-2h-1) = 27.9 Ereq (Emax)-0.455, where:
|Contact: Christine Guilfoy|
American Physiological Society