After familiarization , seven male endurance-trained volunteers , unacclimated to exercise in the heat , performed two experimental trials in 30C ( 60 % relative humidity ) in a crossover fashion separated by at least 7 d. Subjects ingested 150 mgkg ( -1 ) body mass tyrosine ( TYR ) or an isocaloric quantity of whey powder ( PLA ) in 500 mL of sugar-free flavored water in a randomized , double-blind fashion .