The menstrual cycle is a natural, normal process which most females experience, starting from around the age of 11 years (can be earlier or later) and continuing until the onset of menopause around the age of 49-52 years.
The cycle typically occurs over a period of 28 days but can range from 22-35 days in length. During the menstrual cycle there is a cyclical fluctuation of sex hormones (primarily oestrogen and progesterone), which are mediated by the hypothalamic-pituitary axis (a system involving the brain and reproductive organs). Whilst oestrogen and progesterone are the key sex hormones involved in the reproductive system, they are also vital in the regulation of other physiological systems and maintaining all-round health. In particular, oestrogen is a key regulator of bone resorption1 (the process by which the bones are absorbed and broken down by the body), has a cardioprotective role2 (serving to protect the heart or coronary arteries from injury or disease), is involved in the immune response, supports the neural system and it is even involved in cognitive processes3.
Therefore, continuous oestrogen exposure through the menstrual cycle post-puberty and pre-menopause could also reduce risk of other health conditions such as osteoporosis and cardiovascular disease4,5.
The pattern of hormones
The first 14 days of a 28-day cycle are known as the follicular phase, with day 1 marking the onset of menstrual bleeding (menses or the period). Towards the end of the bleeding phase, oestrogen levels start to increase, reaching their peak just prior to ovulation, which occurs on around day 14 of a 28-day cycle.
The follicular phase
FSH (follicle stimulating hormone) steadily increases through this phase, and then as part of a complex feedback loop, once oestrogen levels reach a set point, there is an ensuing dramatic surge in LH (luteinizing hormone), and this in addition to a surge in FSH cause ovulation to occur. Oestrogen levels fall just prior to the LH surge. After ovulation, LH levels rapidly drop off.
The luteal phase
The latter 14 day period is known as the luteal phase and there is a gradual increase in another hormone, progesterone, alongside another increase in oestrogen. Both of these hormones are released in response to the formation of a structure called the corpus luteum, which functions to protect a developing embryo if there has been a fertilisation. If there has not been a fertilisation, progesterone and oestrogen levels reach a peak around day 22, before gradually decreasing, and return to base levels at day 28.
The withdrawal or decline in hormones is the primary trigger for the onset of menstrual blood loss. The cycle then begins again at day 1 with the onset of bleeding (menses or the period).
Throughout the cycle the lining (endometrium) of the uterus also thickens and thins as it prepares for implantation and later pregnancy. Both oestrogen and progesterone are involved in the thickening and development of the endometrial lining. If fertilisation does not occur then the blood supply to the uterus lining is reduced, in the second half of the cycle, as it is no longer required and then the lining is eventually shed, resulting in the onset of the period and bleeding.
Menstrual cycle and exercise performance
Runners and female athletes alike often ask how the menstrual cycle and the differing levels of hormones involved affect performance.
According to prior research, the menstrual cycle has been suggested to have potential detrimental effects on sports performance and training. In a recent study, 51% of elite athletes felt that their symptoms associated with the menstrual cycle adversely affected their performance6 and another study reporting 67% of athletes had symptoms perceived to affect their performance7. Additionally 36.7% of elite athletes have reported heavy menstrual bleeding to affect their performance8.
Studies have also reported a variety of performance alterations during the menstrual cycle, some of which are: muscular performance changes throughout the cycle9 an increased injury risk associated with hormonal fluctuations across the cycle10, increased laxity of the knee joint in the follicular stage of the cycle11 and a reduced communication between the muscles and nerves in those that are classified as amenorrheic (an absence of cycles)12. While others suggest that adaptation to training may be altered13.
Although a recent study, whereby all the current evidence available was evaluated, revealed very few differences within exercise performance across the menstrual cycle, with only a possible slight marginal decline in performance during menstruation (early follicular phase)14, which may be more relevant for athletes at the elite end of the scale looking for marginal gains where feasible.
Currently we do not have a one size fits all answer when it comes to the menstrual cycle and exercise performance, we may never do. What we do know is that the menstrual cycle and its associated symptoms and effects will vary greatly from one individual to another, so what we can do is use this to our advantage and prepare for such inevitable events.
We at the Female Athlete Podcast always advocate for an individualised approach to the menstrual cycle as each female will have their own unique experience and go through their own set of symptoms. What we can do is educate females to learn about their own bodies, understand what is happening at different times of their cycle and manage their symptoms in the best way possible.
Menstrual cycle tracking
Tracking the menstrual cycle is a tool in which the majority of women can incorporate into their daily routines with relative ease, recording information such as the symptoms they’re suffering with on a given day, (ie. lower back pain, abdominal cramps, headaches, change in mood) as well as recording anything out of the ordinary in regard to exercise routine or diet. This will help establish a trend within their own cycle and help prepare for those monthly changes.
To find out more about menstrual tracking and how this can bring out the best in your performance, head to Series 1, Episode 2 of the Female Athlete Podcast where we discuss this in detail. Covering how to map your menstrual cycle, how to optimise your nutrition for different phases and whether you should exercise whilst on your period.
Listen in for some insightful nutrition guidance from Georgie around what foods are best suited for different phases of your cycle, including the importance and benefits of anti-inflammatory foods and antioxidants in phase 1, to counter inflammation common during menstruation.
The menstrual cycle is just one of the so-called ‘taboo’ topics around female health and physiology which is covered on the Female Athlete Podcast. We’re using conversation and education as a tool to empower women and help them feel more confident about their bodies, especially when it comes to exercise.
In previous episodes we’ve spoken to a variety of guests including sports scientists, doctors, breast health experts, athletes suffering with menstrual dysfunctions such as endometriosis and premenstrual dysphoric disorder (PMDD), and we’ve interviewed real women about the impact of long-term oral contraceptive pill use on their bodies and personal experiences of female puberty, menopause and peri-menopause. You can find out more about what we do and listen to previous episodes at femaleathletepodcast.buzzsprout.com.
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