The effects of menstrual cycle phase on the incidence of plateau at V<mml:mo></mml:mover>O2max and associated cardiorespiratory dynamics

The purpose of this study was to examine the effect of menstrual cycle phase on maximal oxygen uptake (VO2max) and associated cardiodynamic responses. A total of 16 active females volunteered of which n=10 formed the non-oral contraceptive pill group (n-OCP), displaying a regular menstrual cycle of 284 +/- 22days (age 206 +/- 16years, height 1699 +/- 64cm, mass 687 +/- 79kg) and n=6 formed the oral contraceptive pill group (OCP) (monophasic pill) (age 217years +/- 216, height 1681cm +/- 68cm, mass 616 +/- 68kg). Each completed four incremental exercise tests for determination of VO2max, cardiac output, stroke volume and heart rate. Each test was completed according to the phases of the menstrual cycle as determined through salivary analysis of 17- oestrodiol and progesterone. Non-significant differences were observed for VO2max across phases and between groups (P>005) with additional non-significant differences for Qmax, HRmax and SVmax between groups. For VO2 during the final 60s of the O2max trial, significant differences were observed between OCP and n-OCP (P<005) with OCP showing zero O2 plateaus in three pseudo-phases. Significant difference observed for a-vO(2dif) n-OCP between premenstruation and menstruation at 30-100% O2max (P<005). Data suggest that the O2 -plateau is effected by monophasic oral contraceptive pill, furthermore these data imply that O2max test outcome is independent of menstrual cycle phase but caution should be applied when evaluating maximal oxygen uptake in females who are administered a monophasic oral contraceptive pill.