Moderate exercise is undoubtedly a positive factor in health. Strenuous exercise in women may lead to disturbances in reproductive function ranging from subtle effects on fertility to hypoestrogenic amenorrhea. Exercise-related menstrual dysfunction is more likely to occur with strenuous exercise, in women who are nulliparous, in women with a history of delayed menarche, in women under age 30, and in women with low body fat. The mechanism by which the menstrual dysfunction develops is, to this point, unknown, but no evidence exists to suggest that it has long-term repercussions on reproductive capacity.