Does exercising on an empty tank mess with your period?

This study looks at how exercising without eating beforehand (fasted) might change menstrual hormones and cycle length in women who regularly run or cycle. Over about 3 months, 64 participants will track their cycles, complete three 90-minute exercise sessions either fed or fasted, and provide saliva samples. The goal is to understand how energy timing affects reproductive health, not to test a treatment.