The Effects of Exercise and Gender on Heat Tolerance Time during Prolonged Heat Exposure

The U.S. Navy has recently begun to increase the number of female sailors stationed aboard ship and personnel staffing ratios on the majority of suface ships are to be 50% male and 50% female by the year 2000. There is concern the Navy's current heat exposure policy may not provide the appropriate guidance for female personnel because these heat exposure standards, commonly referred to as the tliysiological Beat Exposure Limits or PHEL curves, were developed using males. It has been established that most gender differences in thermoregulation are negligible when males and females are evenly matched for factors such as age, acclimation, body size, maximal aerobic capacity, and relative versus absolute workload (1,2,3). However, female sailors within the US. Navy population differ in size, fitness, and body composition from male 'sailors. Additionally, though body size was incorporated in the development of the PHEL curves, application of the PHEL curves is based on personnel performing shipboard tasks at an absolute work rate. We hypothesized that gender differences in thermoregulation would not appear at low activity levels (PHEL 1, P E L 2) and/or low thermal environments, but may begin to appear at a moderate work rate and moderate to high thermal environments. We have previously reported the thermoregulatory responses of males to a PHEL 3 work rate (4,5). The purpose of this study was to compare thermoregulatory responses between males and females to the PHEL 3 work rate which has time-weightedmean metabolic rate of 11 1.7 Warn2.