Core temperature differences between males and females during intermittent exercise: physical considerations

We examined differences in dynamic heat balance between males and females during intermittent exercise. Six males (M) and six females (F) performed three 30-min bouts of exercise (Ex1, Ex2, Ex3) at a constant rate of metabolic heat production (\( \dot{M} - \dot{W} \)) of ~500 W separated by three 15-min periods of inactive recovery. Rate of total heat loss (\( \dot{H}_{\text{L}} \)) was measured by direct calorimetry, while \( \dot{M} - \dot{W} \) was determined by indirect calorimetry. Esophageal (T _es) was measured continuously. Exercise at a constant \( \dot{M} - \dot{W} \) of ~500 W, was paralleled by a similar \( \dot{H}_{\text{L}} \) between sexes at the end of Ex1 (M: 462 ± 30 W, F: 442 ± 9 W, p = 0.117), Ex2 (M: 468 ± 28 W, F: 508 ± 18 W, p = 0.343), and Ex3 (M: 469 ± 17 W, F: 465 ± 13 W, p = 0.657). Consequently, changes in body heat content were comparable after Ex1 (M: 218 ± 21 kJ, F: 287 ± 35 kJ, p = 0.134), Ex2 (M: 109 ± 18 kJ, F: 158 ± 29 kJ, p = 0.179), and Ex3 (M: 92 ± 19 kJ, F: 156 ± 35 kJ, p = 0.136). However, females had greater overall increases in T _es at the end of Ex3 (M: 0.55 ± 0.25°C, F: 0.97 ± 0.26°C, p ≤ 0.05). Differences in core temperature between sexes appear to be solely related to differences in physical characteristics, and not due to concurrent differences in whole-body thermoregulatory responses.