Methodological Recommendations for Menstrual Cycle Research in Sports and Exercise.

INTRODUCTION: The aim of this review is to provide methodological recommendations for menstrual cycle research in exercise science and sports medicine based on a review of recent literature. Research in this area is growing but often reports conflicting results, and it is proposed that some of this may be explained by methodological issues.
METHODS: This review examined the menstrual cycle verification methods used in recent literature on exercise performance over the menstrual cycle identified through a literature search of PubMed and SportDiscus from 2008 until 2018.
RESULTS: Potential changes over the menstrual cycle are likely related to hormone fluctuations; however, only 44% of the selected studies measured the actual concentrations of the female steroid hormones estrogen and progesterone. It was shown that the likely inclusion of participants with anovulatory or luteal phase-deficient cycles in combination with small participant numbers has affected results in recent menstrual cycle research and, consequently, our understanding of this area.
CONCLUSION: To improve the quality of future menstrual cycle research, it is recommended that a combination of three methods is used to verify menstrual cycle phase: the calendar-based counting method combined with urinary luteinizing hormone surge testing and the measurement of serum estrogen and progesterone concentrations at the time of testing. A strict luteal phase verification limit of >16 nmol·L for progesterone should be set. It is also recommended that future research should focus on the inclusion of the late follicular estrogen peak. It is envisaged that these methodological recommendations will assist in clarifying some of the disagreement around the effects of the menstrual cycle on exercise performance and other aspects of exercise science and sports medicine.