Assessing Physiologic Responses To Exercise In The Heat In Unacclimatized, Endurance (aerobic) And Resistance Trained Females

PURPOSE.Sex differences in thermoregulation stem from innate physiological variations in anthropometrics and workload capacity. These differences have not been investigated in trained females with different exercise backgrounds. This study involved exercise in hot and thermoneutral environments with endurance (ET) and resistance (RT) trained unacclimatized females to assess physiologic responses. METHODS. ET and RT females completed a DEXA scan, an aerobic capacity test, and 1 repetition max (1RM) of bench press and back squat. The experimental procedure involved a 75-minute walk at 60% VO2 peak in HOT (33 °C, 50% rh) and NEUTRAL (21 °C, 50% rh) conditions. Heart rate (HR), core temperature (Trec), and respiratory measures (VO2, Ve, and RER) were taken at baseline, and every 15 minutes of exercise. Blood lactate was taken pre- and post-exercise. Cortisol (CORT) and heat shock protein 70 (HSP70) were measured pre-, post-, and 24-hour post-exercise. RESULTS. There were no significant differences in anthropometric measures between the groups. The ET females had significantly higher VO2 peak values (p<.001). The RT females had significantly higher 1RM back squat values (p<.001) and 1RM bench press values (p=.002). There were no significant differences between the two groups in relative VO2, Ve, RER, HR and Trec responses throughout all exercise time points in both conditions. The ET group had significantly lower lactate levels after exercise in the HOT condition compared to the RT group (p<.001). The RT group experienced higher lactate levels after exercise in the HOT condition compared to lactate levels after the NEUTRAL condition (p=.003). There were significant differences in CORT levels pre-exercise in HOT (p=.037), 24 hr post-exercise in HOT (p=.036), and 24 hr post-exercise in NEUTRAL conditions (p<.001) between the groups. There were no significant differences in HSP70 across the respective time points within both conditions. CONCLUSION. These results suggest that training adaptations induced through participating in resistance exercise allow unacclimatized females to tolerate aerobic-based exercise in HOT and NEUTRAL conditions to a similar degree as unacclimatized females with an endurance exercise background although RT females may experience a greater metabolic response to heat stress.