Heat strain at the critical WBGT and the effects of gender, clothing and metabolic rate

Heat strain at the upper limit of thermoregulatory control depends on gender, clothing and metabolic level. Twenty nine acclimated participants (20 men and 9 women) walked on a treadmill at a moderate metabolic rate in the heat wearing five different ensembles. A subset of 15 participants (11 men and 4 women) completed trials for all ensembles at low and high metabolic rates using a progressive heat stress protocol. This allowed each subject to establish a physiological steady state followed by step-wise increases in heat stress to a loss of thermal equilibrium. WBGT crit was the WBGT 5 min prior to a loss of thermal equilibrium and represents the upper limit of thermoregulatory control. As expected, there was an ensemble effect and metabolic rate effect for WBGT crit. Metabolic rate also had significant effects on the measures of heat strain. After adjusting for differences in normalized metabolic rate, there was no gender effect for WBGT crit or T sk. There were significant gender effects for HR, T re and PSI. In conclusion, women exhibited similar heat stress at WBGT crit with higher thermal strain. The gender difference may be explained by a relative difference in fitness. In industrial settings, men and women work at equivalent work rates with the relative workload being greater for women. Women experience a greater physiological strain for a given work rate.