Athletes should drink fluid at rates that exceed their sweat rates.
When sweat leaves the skin's pores, it evaporates into the air, taking some heat with it.
It's not just body temperature that causes sweating. During exercise, heart rate and blood pressure increase, which in turn cause the body to pump out more sweat.
To over come sweating excessive water is needed as water evaporates and comes out while exercising in the form of sweat.
