
The body loses moisture through perspiration as well as through respiration (think of your breath fogging a window). Both of these processes speed up during exercise as the body works to cool itself down with sweat, which evaporates from the skin, taking heat with it, and by breathing harder to get extra oxygen to the muscles. Pile these factors on to a hot summer training session under heavy protective gear, and you have a recipe for some serious fluid loss.
To read the full, original article click on this link: How Much Water Weight Can a Player Lose During a Game?: Scientific American