EFFECTS OF MENSTRUAL CYCLE PHASE AND ORAL CONTRACEPTIVE USE ON INTERMITTENT HIGH-INTENSITY EXERCISE

Abstract

1463 Five women using low-dose, monophasic OC agents (OC group) and ten normally menstruating women (Non-OC group) performed a treadmill protocol on two separate occasions. The Non-OC group were tested in the midfollicular (MFP) and late luteal (LLP) phases of the MC. A two-way ANOVA revealed that body mass, body fat, and maximum heart rate (HRmax) did not vary over the MC. Menstrual phase did not affect resting blood lactate (BLa) and plasma ammonia (NH3) nor the exercise induced increase in BLa and NH3(P<0.05). Aural temperature (Taural) increased with exercise in both phases (P<0.05) however Taural (° C) was higher in the LLP at rest (mean ± SEM; 36.1 [0.1]) and 1 minute post exercise (37.1 [0.2]), when compared to the MFP (35.8 [0.1] and 36.9 [0.2],rest and post 1 respectively, P<0.05). Further analysis showed no significant differences in age, stature, and peak oxygen uptake between the groups, however the OC group were lighter (P<0.05) and had less body fat (P<0.05). Although the pattern of BLa, NH3 and Taural responses of the OC group mimicked that of the Non-OC group, a three-way ANOVA revealed a significant test effect with T1 (performed within 1 week of taking the pill) resulting in higher peak BLa (11.2 [0.2] mmol/L) and NH3 (143.0 [11.7] Umol/L) than when compared to T2, performed 1 week later (BLa, 9.6 [0.4]; NH3, 119.4[21.5] (P<0.05). NH3 was higher in the Non-OC group when compared to the OC group throughout recovery (P<0.05) despite performance time being the same in both groups. No differences were found in BLa, HRmax or Taural between groups. The results suggest: 1) exercise performance does not vary between the MFP and the LLP of the MC, nor does it appear to be affected by the number of days on the pill; 2) an altered metabolism both between groups (Non-OC versus OC) and within the OC group.