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1. Introduction
For a growing number of female athletes, the desire for athletic success can be associated with a high drive for thinness that may lead to the development of low energy availability, menstrual dysfunction, and low areal bone mineral density (aBMD), a condition collectively referred to as the 'female athlete triad'.[1] Alone or in combination, the disorders of the female athlete triad can have a negative impact on health and athletic performance.[2] This condition not only affects high-level female athletes but more generally exercising girls and women.
Low energy availability can be caused by high energy expenditure associated with physical exercise and training, inadequate energy intake, or a combination of both. Energy availability is defined as dietary energy intake minus exercise energy expenditure.[1] Energy availability is considered adequate when energy intake is sufficient to maintain normal routine physiological functions in addition to exercise training. When energy availability is too low, the body tends to reduce the amount of energy that is used for physiological functions such as cellular maintenance, thermoregulation, growth and reproduction.[3] Energy conservation, which tends at restoring energy balance, could explain why stable body weight has been reported in amenorrhoeic athletes.[4-7]
Low energy availability triggers the disruption of the hypothalamo-pituitary-gonadal axis, which leads to menstrual disturbances including amenorrhoea.[1,2,8-14] Amenorrhoea is defined as having no menses for a minimum period of 3 months.[15] Functional hypothalamic amenorrhoea (FHA) is diagnosed by exclusion of situations (e.g. pregnancy) or medical conditions (e.g. hyperprolactinoma, thyroid diseases) that typically cause the absence of menses.[15,16] Athletic amenorrhoea is a form of FHA observed in athletes who display low energy availability. Amenorrhoea represents the most severe menstrual disturbance along a continuum of abnormalities ranging from luteal phase defects, anovulatory cycles, oligomenorrhoea (irregular and inconsistent menstrual cycles lasting from 36 to 90 days[17]) and amenorrhoea.[9] Irregular menses in athletes (oligo- or amenorrhoea) have been associated with a 2- to 4-fold greater incidence of stress fractures[18] and low aBMD, particularly at the spine.[19-26]
The prevalence of oligomenorrhea and amenorrhoea in adult athletes across multiple sports has been reported to range from 12% to 79%.[27-29] In adolescents (<18 years), a high prevalence of oligomenorrhea and amenorrhoea (45-50%) has been reported in sports that emphasize a lean physique, such as ballet dancing and running.[27,30,31]...