Precooling was via chest-deep immersion ( ~ 24 C ) for 1 hour or until core temperature dropped 0.5 C. Participants then cycled at 95 % ventilatory threshold in a hot environment ( temperature = 30 C , relative humidity = 50 % ) until volitional exhaustion , core temperature reached > 39.5 C , or heart rate reached > 95 % of maximum .