If you’re feeling extra hot on your runs, it may not just be the outside temperature. It could be your menstrual cycle speaking to you. 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 your 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. Not a good thing when running on a hot and humid day, when you want to begin the cooling response as soon as possible.
Estrogen has the opposite effect on the hypothalamus, decreasing body temperature, which explains why body temperature is lower during the estrogen-dominant follicular phase.
A higher body temperature during the luteal phase makes it harder to run in the heat during this phase, as runners don’t begin sweating to dissipate heat until they have reached a higher body temperature. They also have a decreased ability to dilate the small blood vessels under the skin, which compromises the ability to release heat to the environment.
Long, intense workouts and races in the heat, such as half-marathons and marathons, can be more difficult during the luteal phase of the menstrual cycle.
If the weather is hot, try to plan your half-marathon or marathon during the cooler body temp follicular phase of your cycle.