Menstrual cycle effects on thermoregulation while exercising in the heat

Area of Science:

• Exercise Physiology
• Reproductive Endocrinology

Background:

• Hormonal fluctuations during the menstrual cycle can impact thermoregulation in women.
• Understanding these changes is crucial for optimizing exercise performance and safety in heat.

Purpose of the Study:

• To investigate the influence of the menstrual cycle phase (early-follicular vs. mid-luteal) on core body temperature, hydration, and perceived exertion during exercise in heat.
• To assess hormonal responses, including estrogen, progesterone, and aldosterone, in relation to thermoregulatory challenges.

Main Methods:

• Eleven healthy women completed two 180-minute trials in a 35°C, 30% relative humidity environment.
• Exercise consisted of three 50-minute intervals at 50% VO2max, with measurements of core temperature, physiological strain index, perceived heat, and perceived exertion.
• Blood samples and body weight were collected pre- and post-exercise to analyze hormonal and hydration status.

Main Results:

• Core body temperature was significantly higher in the mid-luteal phase compared to the early-follicular phase.
• Aldosterone levels increased post-exercise and remained elevated in the mid-luteal phase.
• No significant differences were observed in sweat rate, hematocrit, hemoglobin, or percent dehydration between the menstrual cycle phases.

Conclusions:

• Women exhibit elevated core body temperature during the mid-luteal phase when exercising in heat, associated with higher estrogen and progesterone levels.
• Despite increased core temperature, perceived exertion and heat stress were similar across phases, suggesting altered thermoregulatory mechanisms.
• Aldosterone plays a role in fluid balance during heat exposure, with sustained elevation in the mid-luteal phase.