The influence of the menstrual cycle and hormonal contraceptives on cardiorespiratory fitness in physically active women: A systematic review and meta-analysis

OBJECTIVE: To systematically review and summarize the existing evidence related to the influence of the menstrual cycle (MC) and hormonal contraceptive (HC) use on [Formula: see text] O(2max) in physically active women. METHODS: This systematic review and meta-analysis conforms to the PRISMA statement guidelines. Four (sub-)meta-analyses were performed. Two focused on longitudinal studies examining the same women several times to compare the [Formula: see text] O(2max) during the different menstrual phases or oral contraceptive (OC) use and withdrawal. Two meta-analyses examined if there is a difference in [Formula: see text] O(2max) between OC users and normally menstruating women by analyzing cross-sectional studies assigning physically active women to one of these two groups as well as intervention-based studies (cross-over studies, randomized controlled trials considering only the data of the intervention group) comparing women intra-individually with and without OCs. RESULTS: Nine of the included studies (107 women) evaluated the influence of the MC, five studies (69 women) the impact of OCs on [Formula: see text] O(2max), and six studies investigated both topics (88 women). A mean difference of [Formula: see text] O(2max) −0.03 ml/kg/min (95%CI –1.06 to 1.01) between the early follicular and luteal menstrual phase was observed. Between the active and inactive phases of OCs, a mean difference of −0.11 ml/kg/min (95%CI –2.32 to 2.10) was found. The inter-individual comparison of naturally menstruating women and OC users showed a mean difference in [Formula: see text] O(2max) of 0.23 ml/kg/min (95% CI –2.33 to 2.79) in favor of OC use. The intra-individual comparison of the same women showed a mean decrease in [Formula: see text] O(2max) of −0.84 ml/kg/min (95% CI –2.38 to 0.70) after a new start with OCs. CONCLUSIONS: Our meta-analyses showed no effects of the MC or the OCs on [Formula: see text] O(2max). More high-quality studies are needed determining the MC phases more precisely, including OCs with the current standard formulations and comparing the influence of different progestins.