Body temperature changes rhythmically throughout the menstrual cycle, peaking during the luteal phase in response to the surge in progesterone. Progesterone acts on your brain’s hypothalamus, which increases set-point temperature.
A higher body temperature increases the threshold for dissipation of heat. So a woman’s body must reach a higher temperature before her thermostat compensates and begins to cool itself. Estrogen has the opposite effect on the hypothalamus, decreasing body temperature, which is why body temperature is lower during the estrogen-dominant follicular phase.
The increased body temperature during the luteal phase remains elevated when running and when running in the heat. A higher body temperature during the luteal phase makes it harder to run in the heat during this phase, as women runners don’t begin sweating to dissipate heat until they have reached a higher body temperature.
If the date of your long race, such as a half-marathon or marathon (especially in the heat), falls during the luteal phase of your menstrual cycle, when progesterone is high, it’s important to focus on keeping cool and staying hydrated.