Does exercising on an empty tank mess with your period?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * participates in structured running or cycling exercise for at least 30 minutes on 3 or more days per week * accustomed to exercising for 90 minutes or more * has regular periods every 21-35 days * have not taken hormonal contraceptives for at least the past 6 months * is not currently or trying to become pregnant or breastfeeding, and has not been pregnant or breastfeeding in the past 12 months * does not currently have a diagnosis of a major menstrual cycle disorder (i.e., amenorrhea, polycystic ovary syndrome \[PCOS\], endometriosis, ovarian cancer, ovarian insufficiency, uterine or endometrial cancer) * does not currently have a metabolic disease (i.e., hypothyroidism, hyperthyroidism, Cushing disease, Addison's disease, diabetes, congenital adrenal hyperplasia) * does not currently have a major cardiovascular or respiratory disease Exclusion Criteria: * miss more than 7 consecutive days of aerobic activity (i.e., running, cycling, cross training) * demonstrate clinical low energy availability as defined as energy availability \<30 kcal/kg fat free mass * report menstrual cycle lengths \<21 or \>35 days in the first 2 months of at-home monitoring * do not demonstrate an anticipated rise in luteinizing hormone and progesterone in the first 2 months of at-home monitoring * begin taking a hormonal contraceptive * become pregnant * are diagnosed with a menstrual cycle disorder (i.e., amenorrhea, polycystic ovary syndrome \[PCOS\], endometriosis, ovarian cancer, ovarian insufficiency, uterine, or endometrial cancer) * are diagnosed with a metabolic disease (i.e., hypothyroidism, hyperthyroidism, Cushing disease, Addison's disease, diabetes) * are diagnosed with a major cardiovascular or respiratory disease * are unable to follow instructions for any of the procedures