Sexual variations in thermoregulation during heat stress

Four male and three female physically fit, but untrained subjects performed a treadmill walking task in neutral (25 degrees C), warm (32 degrees C) and hot (40 degrees C) environments. The treadmill grade for each subject was based on 50% VO2 max as determined in a neutral environment. Environmental exposures were 2 h in duration divided into 40 min of rest, work, and recovery. No distinct sexual differences in rectal and skin temperature responses were observed in the three environments. The male subjects had higher heart rates and greater evaporative weight losses during exercise in all environments. The female subjects experienced less severe increases in metabolic requirements during work in the warm and hot environments than the male subjects. The greater percentage of increase in heart rates relative to changes in the metabolic cost of work in the females suggested a greater cardiovascular component of thermal regulation in the female than in the male subjects. The results of this study suggest that physically fit females are capable of working in the heat about as well as males when work load is relative to individual maximal aerobic capacity.