Author and graduation date: Gretchen VURBEFF, December, 2000

Committee members: Michael Buono (Chair), Patricia Patterson, John Martin

Thesis title: The Influence of the Menstrual Cycle on Thermoregulatory Response to Exercise in Women

The effect of the normal menstrual cycle on the thermoregulatory response to endurance exercise was investigated in 7 naturally menstruating women (age 29.4 ± 4.4 years, peak V02 42.7 + 8.4 ml/kg/min). No subjects had been on oral contraceptives for at least 12 months. In order to estimate phase of cycle for exercise testing, subjects recorded normal menstrual cycle history two months prior to testing and throughout the two-month testing period. Exercise bouts were performed during two phases: early follicular phase (days 3-7 after onset of menstruation) and mid-luteal phase. Capillary blood samples were taken prior to each exercise session and analyzed for progesterone levels to assure phase of cycle. Each subject cycled on an ergometer at approximately 60% of their peak V02 for 60 min. in an environment of 30oC and 50% relative humidity. Measurements included: rectal temperature (Tre), heart rate (HR), stroke volume (SV), forearm blood flow (FBF), skin blood flow (SkBF), whole body sweat rate (WBSR), and local sweat rate (LSR) to identify differences between the two phases. Values for TIe (p = .012) and HR (p = .008) were significantly higher during exercise in the luteal than the follicular phase. However, SV, FBF, SkBF, WBSR, and LSR differences were nonsignificant between luteal and follicular phase. The findings suggest that rectal temperature and heart rate are influenced by menstrual phase. The higher progesterone levels shown during the mid-luteal phase may contribute to the higher core temperature, which in turn increases heart rate. Future consideration should be given to determine the overall effect of the normal menstrual cycle on thermoregulation and performance of active women.

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