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Menstrual cycle disturbances
Throughout the reproductive years, females can experience numerous abnormalities in their menstrual cycle. Many of them can occur without being noticed while others are impossible to miss.

Throughout the reproductive years, females can experience numerous abnormalities in their menstrual cycle. Many of them can occur without being noticed while others are impossible to miss. In this article, we will describe the most common ones such as secondary amenorrhea, luteal phase defect and an-ovulation.

Amenorrhea

Amenorrhea, if not caused by the pregnancy, lactation or menopause, indicates a defect in the hypothalamic-pituitary-ovarian axis. It is defined as an absence of menstruation for three months or more (secondary amenorrhea), or the absence of first period (menarche) by the age of 15 (primary amenorrhea). Amenorrhea is not a diagnosis, but rather a sign of a disorder. Numerous studies have found associations between the increased incidence of amenorrhea and undertaking regular strenuous exercise, following a strict diet or being under psychological stress. Women losing the menstruation as a result of those are classified as having functional amenorrhea.

Laboratory analysis of hormones in the blood usually reveals lower levels of pituitary hormones (LH, FSH), lower ovarian hormone levels (oestrogen) and higher concentrations of adrenal hormones (cortisol, DHEAS) indicating increased stress. Despite the lower levels of oestrogen, many women do not show symptoms of oestrogen deficiency.

Due to the social norms that encourage dieting, weight loss and thinness the prevalence of amenorrhea is on the rise. Incidence of amenorrhea in the general population is 3-4% while among athletes the prevalence is much higher ranging from 14 to 25% and even up to  44% based on some studies. Women engaging in endurance exercises frequently experience disordered attitudes towards eating and are thus at a greater risk for hypothalamic amenorrhea. A renown research De Souza and colleagues found that strenuous aerobic exercise combined with a restrictive diet was able to induce a menstrual dysfunction.  Often the amenorrhea is desired among female athletes, however, its consequences are detrimental. Upon the onset of amenorrhea, the bone mass starts to decrease in turn increases the risk for stress fractures. Unfortunately, in the absence of oestrogen, neither a high calcium intake nor strength exercise regimen cannot restore the lost bone mass, which would accrete during puberty.

Anovulatory cycle

LUTEAL PHASE DEFECT

If the amenorrhea is one of the obvious signs of a defect in the hypothalamic-pituitary-ovary axis, luteal phase defect can remain undiagnosed as the length of the cycle might not differ. In a normal scenario, the luteal phase lasts between 10 and 14 days, whereas in women with luteal phase defect it lasts less than 10 days. In women with luteal phase defect, the ovulation is occurring however, the corpus luteum is not producing a sufficient amount of progesterone and thus the pregnancy cannot be supported. Hereby it must be stated that the training volume and intensity are not a prerequisite for menstrual dysfunctions like luteal phase defect. De Souza and colleagues observed a shorter luteal phase in recreational women performing only 3 hours of running per week.

Luteal phase defect

OVULATORY DISORDERS

During the anovulatory cycle, the egg is not released from the ovary. It is not uncommon for the women to experience an anovulatory cycle without missing their menstruation, especially in pubertal years and around the menopause. Anovulation is diagnosed by checking the progesterone levels, the lining of the uterus and performing laboratory tests. However, by measuring basal body temperature every morning, one can notice the absence of temperature spike around the time of ovulation. The association between ovulation, body mass index (BMI) and exercise are U- shaped. If on one hand obesity can be a reason for infertility and anovulation, on the other hand having low BMI, excess training and high-intensity training also raises the chances of above-mentioned disorders. However, over-exercise can disturb the process of ovulation not only in underweight women but also in those with normal body weight. The reason does not lie only in the physical stress induced on the body but mainly due to low energy availability and improper fuelling.

It is a great hype to talk about amenorrhea as a consequence of relative energy deficiency in sport (REDs) or a female athlete triad. Yet, luteal phase defect and anovulation also show the stress the body is going through and disturbance of the hypothalamic-pituitary-ovary axis. As the common link of all above described menstrual disturbances is energy deficit, it is of greatest importance to have a sufficient energy intake and to properly plan nutrition around training to support adaptation, recovery and overall health.

De Souza, M. J., B. E. Miller, A.B.Loucs, et al. High frequencyof LPD and anovulation in recreational women runners: bluntedelevation in FSH observed during luteal-follicular transition. J. Clin. Endocrinol. Metab.83:4220–4232, 1998

De Souza, M.J., 2003. Menstrual Disturbances in Athletes: A Focus on Luteal Phase Defects. Medicine & Science in Sports & Exercise.. doi:10.1249/01.mss.0000084530.31478.df

Hakimi, O., Cameron, L. Effect of Exercise on Ovulation: A Systematic Review. Sports Med 47, 1555–1567 (2017). https://doi.org/10.1007/s40279-016-0669-8

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