The key to this energy exchange is good ol' sweat. For every gram of perspiration which evaporates from your skin, you lose approximately 2.43 kilojoules of energy. The men who drank hot water gained 52 extra kilojoules of heat from the water. But when the sweat started pouring off their bodies, the men also lost 108 kilojoules of heat from sweat evaporation. When it came to chilly drinks, the opposite happened. The men produced much less sweat, and therefore experienced less evaporation. While the cold water cooled them down by 138 kilojoules, that wasn't enough to counteract the 159 kilojoules retained from decreased evaporation on their skin. When the cyclists drank room temperature water, the amount of heat they gained versus the amount they lost stayed the same.