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 O2max 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 O2max during the different menstrual phases or oral contraceptive (OC) use and withdrawal. Two meta-analyses examined if there is a difference in O2max 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 O2max, and six studies investigated both topics (88 women). A mean difference of O2max -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 O2max 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 O2max 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 O2max. 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