Each of the three experimental trials will be separated by at least 48 hours. On each of the three trials, participants will be immersed up to the level of the sternal notch in 8˚C for up to 60 minutes or until the core temperature falls to 35˚C. Demerol will be administered by a licensed physician during the final 10 minutes of immersion to suppress shivering. Participants will then exit the water, be dried off and rewarmed with either head or torso warming techniques. After removal from the water, an extra dosage of demerol might be given to suppress shivering only if its necessary. The rewarming will be administered for 120 minutes or until the core temperature returns to normal values (̴36.5-37˚C). The order of warming methods will follow a modified balanced design with control being first and the two active warming conditions being balanced.