Influence of Menstrual Cycle Phase and Oral Contraceptive Use on the Time-of-Day Effect on Maximal Anaerobic Power

Abstract

This study was designed to analyse the time-of-day effect in maximal anaerobic power, and the influence of menstrual cycle phase and oral contraceptive use on any diurnal effect. Diurnal variations in maximal cycling power were studied in 11 eumenorrheic women and 10 women using monophasic oral contraceptives. Subjects were tested at 09:00, 14:00 and 18:00 hours, assigned randomly on separate days, in the mid-follicular or pseudo-follicular phase (days 7, 8, 9) and in the mid-luteal or pseudo-luteal phase (days 19, 20, 21) of the menstrual cycle. The order of test sessions was randomly assigned. Body mass was measured before, and rectal temperature after, a standardized 15-min warm-up. Maximal cycling power (Pc) was determined by a force-velocity test. Rectal temperature significantly increased from morning (09:00) to afternoon (14:00 and 18:00) in follicular and luteal phases for eumenorrheic subjects, and in days 7–9 and days 19–21 for contraceptive users (p < 0.05). No significant interaction effects (time of day × group × cycle phase) were observed for rectal temperature. In eumenorrheic subjects, Pc increased significantly from 09:00 to afternoon during the follicular phase (P < 0.05). In contrast, no significant time-of-day effects were observed during the luteal phase in eumenorrheic subjects, and at any cycle phase in contraceptive users. Analysis of variance failed to reveal any significant interaction effects for Pc. This study suggested that the time-of-day effect on maximal anaerobic power could be damped during the luteal phase of eumenorrheic women or at any cycle phase by oral contraceptive use.