Background: The skin is the primary interface between ambient temperature and the human thermoregulatory system. It has been reported that approximately 25-50% of POAH neurons are activated by warming of the skin or spinal cord, proving the importance of skin temperature inputs in thermoregulatory responses. In addition, it remains unclear whether males and females perceive thermal stress similarly during exercise and at rest in hot and/or cold environments. Research examining the female endurance athlete and warfighter is severely lacking and thus, it is paramount to identify the effects of sex and menstrual cycle phase in females on skin temperature (Tsk), and thermal sensation (TS). The purpose of the current study is to identify physiological differences in thermoeffectors between males and females during exercise and rest in hot and cold environments. Methods: Twelve males and twelve females (males: 22 ± 2 years, females: 23 ± 3 years), completed exercise trials in extreme hot (EH) (35°C and 50%) and extreme cold (EC) (~0°C and 50%) conditions. Males completed two trials (EH and EC) and females completed four trials over two menstrual cycle (MC) phases (follicular: EH-F, EC-F; luteal: EH-L, EC-L). Each trial consisted of three 30 min blocks of exercise (B1, B2, B3) separated by 10 min of rest (R1, R2, R3). Mean weighted Tsk was calculated using Ramanathan’s 4-points formula. Verbal reports of TS were recorded during all trials. The relationship between Tsk and TS was analyzed using Pearson’s correlation coefficient test. Results: During the EC trial, females in the follicular phase had a significantly lower Tsk compared to males (p = 0.02). Furthermore, the times (T) at which follicular females had significantly lower Tsk compared to males include T20 (p = 0.05), T35 (p = 0.007), T40 (p = 0.01), T50 (p = 0.02), T60 (p = 0.02), T70 (p = 0.02), T75 (p = 0.03), T80 (p = 0.01), T100 (p = 0.03), T115 (p = 0.02), and T120 (p = 0.04). No significant differences in Tsk were observed between MC phase during the EC trial (p = 0.38). During the EH trial, no significant differences in Tsk were observed between sex (p = 0.24) or MC phase (p = 0.86). During the EH and EC trials, no significant differences in TS were observed between sex (p = 0.62, p = 0.07 ) or MC phase (p = 0.96, p = 0.30). A moderately strong correlation was found between Tsk and TS for EH-F (R2 = 0.49). In addition, a fair correlation was found between Tsk and TS for males EH, females EH-L, females EC-L and females EC-F trials (R2 = 0.35, R2 = 0.34, R2 = 0.10, R2 = 0.30), respectively. Conclusion: Females, regardless of MC phase, had elevated Tsk compared to males during the EH trial and decreased Tsk compared to males during the EC. Females, particularly during the follicular phase, could be at a higher risk for sustaining cold injuries (e.g., frostnip, frostbite) compared to males.
