Background: Limited data exists on the influence of menstrual cycle (MC) phase and oral contraceptive (OC) phase on physical performance in endurance-trained females due to poor control regarding MC verification and differentiation. We aimed to evaluate exercise performance and the respiratory response to exercise in three distinct phases of the MC and OC cycle in endurance-trained females.
Methods: Using a prospective cohort study design, we recruited trained females (Vo<inf>2max</inf> 52±4 mL O<inf>2</inf>/min/kg) who were either not using oral contraceptives (NOC) or using monophasic OCs. NOC were tested in the early and late follicular phase (FP) and the mid-luteal phase (LP). OC-users were tested in the withdrawal phase (WP) and two times in the active OC phase (OCP). The test battery included DXA scans, blood sampling, a submaximal bike test, a maximal isometric knee-extensor strength test, 4 and 20-second bike sprints, and a 6 min time trial on a bike. MC phases were verified by the use of ovulation kits and circulating sex hormone levels.
Results: After the exclusion of four NOCs due to inadequate sex hormone levels, 11 NOC and 13 OC users were included in the final analysis. 6 min time trial performance, sprint performance, and most submaximal exercise intensity variables did not differ between MC phases and OC cycle phases. However, in NOC, ventilation (L/min) during exercise at 30% of aerobic peak power was 7.6% lower in the late FP compared to the LP (P<0.05). In OC users, muscle strength was 3.9% higher in the early OCP compared to WP (P<0.05), whereas body mass was higher in the late OCP compared to WP (P<0.05).
Conclusions: Collectively, our study suggests that MC phase and OCP influence exercise performance to a limited extent in endurance-trained females.