Bone mass increases in response to exercise but decreases in hypogonadism. Thus, it is increased in woman athletes who have normal menses but is decreased in those with amenorrhea.1-3 This decrease in bone mass is associated with increased frequency of stress fractures of a lower extremity.2,3
Exercise-induced menstrual irregularity is common. Between 25% and 40% of highly trained endurance athletes report fewer than three menses per year.4 Menstrual irregularities are more likely if training is begun at the time of, or shortly after, the menarche, before complete maturation of the hypothalamic-pituitary-ovarian axis.2,4
Why is there an association between amenorrhea and decreased bone mass? The decrease could be due to delayed skeletal maturation, increased rate of bone loss, or both. Most of the women studied so far have been in the age range of 18 to 29 years. Although linear growth ceases with closure of the epiphyses,
Riggs BL, Eastell R. Exercise, Hypogonadism, and Osteopenia. JAMA. 1986;256(3):392–393. doi:10.1001/jama.1986.03380030094037
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