Can too much running or stress throw off your period? study seeks answers

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 4 days per week or more * have regular periods every 21 to 35 days * have not used hormonal contraceptives for at least the past 6 months * are not currently or trying to become pregnant or are breastfeeding, and have not been pregnant or breastfeeding for the past 12 months * have never been diagnosed with a menstrual cycle disorder (e.g., menorrhagia, amenorrhea, dysmenorrhea, polycystic ovary syndrome \[PCOS\], endometriosis, premenstrual dysphoric disorder \[PMDD\], menstrual migraines, ovarian cancer, ovarian insufficiency, uterine or endometrial cancer) * have never been diagnosed with a metabolic disease (e.g., hypothyroidism, hyperthyroidism, Cushing disease, Addison's disease, diabetes) Exclusion Criteria: * missing \> 4 consecutive days of aerobic exercise (i.e., running, cycling, cross training) if assigned to the exercise intervention groups * they indicate they "Could not participate at all due to a health problem" or have had to modify their exercise training, felt their injury, illness, or other health problem has affected their exercise performance, or experienced symptoms/ health complaints greater than "To a minor extent" on the Oslo Sports Trauma Research Center Questionnaire (exercise training intervention group) * demonstrate clinical low energy availability as defined as energy availability \<30 Kcal/kg fat free mass in the first two months of at-home monitoring * report menstrual cycle lengths \<21 days or \>35 days in the first two months of at-home monitoring * do not demonstrate an anticipated rise in progesterone levels during the latter half of their cycle and luteinizing hormone levels at mid-cycle compared to tests taken during the first few days after menses in the first two months of at-home monitoring * begin taking a hormonal contraceptive * become pregnant * are diagnosed with a menstrual cycle disorder (e.g., menorrhagia, amenorrhea, dysmenorrhea, polycystic ovary syndrome \[PCOS\], endometriosis, premenstrual dysphoric disorder \[PMDD\], menstrual migraines, ovarian cancer, ovarian insufficiency, uterine or endometrial cancer) * are diagnosed with a metabolic disease (e.g., hypothyroidism, hyperthyroidism, Cushing disease, Addison's disease, diabetes), 10) are diagnosed with a major cardiovascular disease, respiratory disease, or musculoskeletal injury * are unable to follow instructions for any of the procedures