In brief: The responses of four interior linemen and four backs were compared during an hour of treadmill walking in a football uniform at 25% of VO2max in a control environment (25 C dry bulb, 48% relative humidity) and a hot, wet environment (35 C dry bulb, 80% relative humidity. After the work session each subject completed two 75-second sprints at 8 mph. The linemen's VO2max was significantly lower and their percent body fat was greater than that of the backs. At the end of the experimental sessions there were significant differences in percent of heat load stored, rectal temperature, heart rate, and mean skin temperature, indicating that the linemen were not able to regulate body temperature as well as the backs in the hot environment.