Thermophysiological responses to occupational heat stress during simulated wildland firefighting in females and males: influence of fitness and body composition

This study compared thermophysiological responses to prolonged exercise during prolonged occupational heat stress in female and male participants involved in wildland firefighting activities while wearing standard personal protective equipment. Twenty-two participants (11 females and 11 males) performed a graded exercise test followed by a prolonged submaximal protocol simulating wildfire suppression tasks in a controlled environment (30 °C, 30% relative humidity). Physiological responses, gastrointestinal temperature (T g ), chest skin temperature (T skin ), sweat production, and heat balance components were evaluated. Females exhibited higher mean values for most physiological variables, except rating of perceived exertion, which was higher in males. However, when responses were analyzed at matched relative exercise intensities, no meaningful sex-related differences were observed in T g , whereas chest T skin and heart rate remained higher in females. Body fat percentage was positively associated with T g and chest T skin ( r= 0.55 and 0.53), whereas VO 2max was negatively correlated with T g ( r= −0.47). This relationship disappeared when VO 2max was normalized to lean body mass. Heat dissipation pathways differed between groups: males showed greater evaporative heat loss, whereas females exhibited a greater contribution of dry heat exchange. These findings suggest that individual body composition and aerobic fitness may contribute to variability in thermophysiological strain during occupational uncompensable heat stress.