We performed a prospective study of 28 initially untrained college women with documented ovulation and luteal adequacy to determine whether strenuous exercise spanning two menstrual cycles would induce menstrual disorders. To ascertain the influence, if any, that weight loss might exert, we randomly assigned the subjects to weight-loss and weight-maintenance groups. Subjects were expected to run 4 miles (6.4 km) per day, progressing to 10 miles (16.1 km) per day by the fifth week, and to engage daily in 31/2 hours of moderate-intensity sports. The normalcy of the menstrual cycles during the period of exercise was judged independently according to clinical and hormonal criteria, the latter comprising serial measurements of gonadotropin and sex-steroid excretion. A higher percentage of abnormalities proved to be detectable by hormonal means (P less than 0.02). Only four subjects (three in the weight-maintenance group) had a normal menstrual cycle during training. In the weight-loss group, the number of women who had luteal abnormalities as compared with those who lost the surge in luteinizing hormone altered significantly over time, the latter occurring more frequently (P less than 0.01) as training progressed. Within six months of termination of the study, all subjects were again experiencing normal menstrual cycles. We conclude that vigorous exercise, particularly if compounded by weight loss, can reversibly disturb reproductive function in women.

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Age at menarche and menstrual periodicity of 21 college swimmers and 17 runners were studied in relation to the age of initiating training. The 18 premenarche-trained athletes had a mean menarcheal age of 15.1 +/- 0.5 years, whereas the 20 postmenarche-trained athletes had a mean menarcheal age of 12.8 +/- 0.2 years, similar to that of the college control subjects, 12.7 +/- 0.4 years. Each year of training before menarche delayed menarche by five months (0.4 years). Of the premenarche-trained athletes, 61% had irregular menstrual cycles and 22% were amenorrheic, whereas 60% of the postmenarche-trained athletes had regular menstrual cycles and none were amenorrheic. Training increased the incidence of oligomenorrhea and amenorrhea among both premenarche- and postmenarche-trained athletes. Metabolic and hormonal changes consequent to an increased lean/fat ratio may explain these findings.

Melatonin was measured in plasma of seven women volunteers before and after serial acute submaximal exercise tests performed during the course of a two-month, progressive endurance training program. Plasma melatonin increased during all exercise sessions and declined towards baseline values when re-measured thirty minutes after completion of each exercise. This finding indicates that vigorous physical activity elicits transient increases in plasma melatonin in both sedentary and trained women.