The mother of menstrual cycle research is here! I spoke with Dr. Jerilynn Prior, one of my personal heroines, about her early and more recent work on menstrual cycles, perimenopause, and estrogen. Dr. Prior made several important interventions in clinical research on the menstrual cycle, asking: Why are we comparing two groups of women who are so different, then blaming all those differences on physical activity? Why are we acting as though physical activity is so damaging to fertility? And, why do we do so little to translate this work to the menstruators who so desperately need it?