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 (M - W) of similar to 500 W separated by three 15-min periods of inactive recovery. Rate of total heat loss (H-L) was measured by direct calorimetry, while M - W was determined by indirect calorimetry. Esophageal (T-es) was measured continuously. Exercise at a constant M - W of similar to 500 W, was paralleled by a similar H-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 degrees C, F: 0.97 +/- 0.26 degrees 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.