Fatty tissue provides a site for steroid hormone inter-conversion thus maintaining sufficient circulating levels of oestrogen. There are many factors which may influence disruption of menses, including weight loss, low weight, nutritional inadequacy, physical or emotional stress, and levels of certain hormones such as endogenous opiates and cortisol. It is likely that the cause lies in a combination of factors rather than one alone. Menstrual dysfunction does not only involve total absence or irregular menstruation, but also luteal phase deficiency and anovulation - both of which influence fertility. Menstruation, puberty and the menopause.
Girls tend to reach puberty earlier than boys.
This means the advantages of early maturity seen in the junior boys ranks are less prevalent in girls racing. It also means that whilst 13 year old girls will often be able to beat boys of the same age in races, by the age of 14 or 15 when the boys have started to go through puberty the advantage has been lost. Excessive exercise tends to delay puberty by about 5 months for every year of training with the associated medical, physical and psychological problems. At the other end of the scale there is no evidence that exercise has any effect on the date of the menopause. Exercise will however protect against some of the side effects of the menopause such as fatigue and bone loss although over-training may exacerbate the problems.