EFFECTS OF THE MENSTRUAL CYCLE ON SERUM CORTISOL DURING MODERATE AND HIGH INTENSITY EXERCISE 1147

Abstract

Twelve males, seven females on oral contraceptives (OC), and five hormonal contraceptive free females (NO-OC) cycled at both moderate (MOD, 60% VO2 peak) and high (HI, 80% VO2 peak) intensities. In MOD subjects rode for three 30 min bouts (25 min cycle, 5 min rest) and for one bout in HI. Males completed each test once while females completed each test twice, once during the follicular phase (FOL, 2-6 days post menses) and once during the luteal phase (LUT, 22-26 days post menses). Serial blood samples were collected and analyzed for serum cortisol levels (CORT) at rest, during exercise, and in recovery. Gender had no effect on CORT response to exercise in either MOD or HI. OC users had higher CORT at all time points in comparison to NO-OC in both MOD (p=0.016) and HI (p=0.002). At rest OC users had 50% higher CORT compared to NO-OC. Menstrual phase had no effect on CORT in NO-OC. However in OC, LUT CORT was consistently higher compared to FOL. This effect was more obvious in HI. Although these data are based on a small population, they suggest that OC use could have a significant effect on performance, especially during endurance exercise where metabolic regulation is more important. Further studies on the influence of OC use on metabolic responses during exercise are warranted.