The menstrual cycle
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 (in the absence of pregnancy and/or hormonal contraception use).
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 resorption (the process by which the bones are absorbed and broken down by the body), has a cardio protective role (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 processes.
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 disease.
The follicular phase (phases 1 & 2)
The first 14 days of a 28-day cycle are known as the follicular phase (phases 1& 2).
This phase starts with menstruation (phase 1) with day one marking the onset of menstrual bleeding. Oestrogen and progesterone levels are at their lowest during your period (phase 1) and the days leading up to your period (phase 4).
Oestrogen levels increase throughout phases 1 and 2. Once they 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, which is normally around day 14 of a typical 28-day cycle. Oestrogen levels fall just prior to the LH surge.After ovulation, LH levels rapidly drop off.
The luteal phase (phases 3 & 4)
After ovulation, the second 14 days are known as the luteal phase (phases 3 & 4).
The latter 14 days sees a gradual increase in 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 (in a typical 28 day cycle).
The withdrawal or decline in hormones is the primary trigger for the onset of menstrual blood loss. The cycle then begins again at day one with the onset of bleeding (getting your period).
The decrease in hormones triggers an inflammatory response. This is thought to be part of the cause of PMS symptoms.
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 the lining is eventually shed, resulting in the onset of the period and bleeding.
At FitrWoman we always advocate for an individualised approach to the menstrual cycle as each person will have their own unique experience and go through their own set of symptoms. What we aim to do is help educate people 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.
The FitrWoman app is designed for you to track your cycle and train smarter by providing personalised training and nutritional suggestions tailored to the changing hormone levels throughout your cycle.
*Contributions to this article come from the Female Athlete Podcast (Dr Georgie Bruinvels and Dr Jess Piasecki)
Chen, F.P., K.C. Wang, and J.D. Huang, Effect of estrogen on the activity and growth of human osteoclasts in vitro. TaiwanJ Obstet Gynecol, 2009. 48(4): p. 350-5.
Iorga, A., et al., The protective role of estrogen and estrogen receptors in cardiovascular disease and the controversial use of estrogentherapy. Biol Sex Differ, 2017. 8(1): p. 33.
Vincent, K. and I. Tracey, Hormones and their Interaction with the PainExperience. Rev Pain, 2008. 2(2): p. 20-4.
Bae, J., S. Park, and J.W. Kwon, Factors associated with menstrual cycle irregularity and menopause. BMC Womens Health, 2018. 18(1):p. 36.
Mumford, S.L., et al., The utility of menstrual cycle length as an indicator of cumulative hormonal exposure. J Clin Endocrinol Metab,2012. 97(10): p. E1871-9.
Martin, D., et al., Period Prevalence and Perceived Side Effects ofHormonal Contraceptive Use and the Menstrual Cycle in Elite Athletes. IntJ Sports Physiol Perform, 2017: p. 1-22.
Findlay, R.J., et al., How the menstrual cycle and menstruation affect sporting performance: experiences and perceptions of elite female rugby players. Br J Sports Med, 2020.
Bruinvels, G., et al., The Prevalence and Impact of Heavy MenstrualBleeding (Menorrhagia) in Elite and Non-Elite Athletes. PLoS One,2016. 11(2): p. e0149881.
Pallavi, L.C., U.J. D Souza, and G. Shivaprakash, Assessment ofMusculoskeletal Strength and Levels of Fatigue during Different Phases ofMenstrual Cycle in Young Adults. J Clin Diagn Res, 2017. 11(2):p. CC11-CC13.
Herzberg, S.D., et al., The Effect of Menstrual Cycle andContraceptives on ACL Injuries and Laxity: A Systematic Review andMeta-analysis. Orthop J Sports Med, 2017. 5(7): p.2325967117718781.
Chidi-Ogbolu, N. and K. Baar, Effect of Estrogen on MusculoskeletalPerformance and Injury Risk. Front Physiol, 2018. 9: p.1834.
Tornberg, Å., et al., Reduced Neuromuscular Performance in Amenorrheic Elite Endurance Athletes. Med Sci Sports Exerc, 2017. 49(12):p. 2478-2485.
Sung, E., et al., Effects of follicular versus luteal phase-based strength training in young women. Springerplus, 2014. 3:p. 668.
McNulty, K.L., et al., The Effects of Menstrual Cycle Phase on ExercisePerformance in Eumenorrheic Women: A Systematic Review and Meta-Analysis. SportsMed, 2020. 50(10): p. 1813-1827.
Kato, I., et al., Epidemiologic correlates with menstrual cycle length in middle aged women. Eur J Epidemiol, 1999. 15(9): p.809-14.
Lateef, O.M. and M.O. Akintubosun, Sleep and Reproductive Health. JCircadian Rhythms, 2020. 18: p. 1.
Nagma, S., et al., To evaluate the effect of perceived stress on menstrual function. J Clin Diagn Res, 2015. 9(3): p.QC01-3.
Palm-Fischbacher, S. and U. Ehlert, Dispositional resilience as a moderator of the relationship between chronic stress and irregular menstrual cycle. J Psychosom Obstet Gynaecol, 2014. 35(2): p. 42-50.
DREW, F.L., The epidemiology of secondary amenorrhea. JChronic Dis, 1961. 14: p. 396-407.
Barsom, S.H., et al., Association between psychological stress and menstrual cycle characteristics in perimenopausal women. Womens HealthIssues, 2004. 14(6): p. 235-41.
Rafique, N. and M.H. Al-Sheikh, Prevalence of menstrual problems andtheir association with psychological stress in young female students studying health sciences. Saudi Med J, 2018. 39(1): p. 67-73.
Fenster, L., et al., Psychological stress in the workplace and menstrual function. Am J Epidemiol, 1999. 149(2): p.127-34.
McIntosh, J.E., et al., Predicting the luteinizing hormone surge:relationship between the duration of the follicular and luteal phases and thelength of the human menstrual cycle. Fertil Steril, 1980. 34(2):p. 125-30.
Halbreich, U., The etiology, biology, and evolving pathology of premenstrual syndromes. Psychoneuroendocrinology, 2003. 28Suppl 3: p. 55-99.
Choi, D., et al., The impact of premenstrual symptoms on activities ofdaily life in Korean women. J Psychosom Obstet Gynaecol, 2010. 31(1):p. 10-5.
Kahyaoglu Sut, H. and E. Mestogullari, Effect of Premenstrual Syndromeon Work-Related Quality of Life in Turkish Nurses. Saf Health Work,2016. 7(1): p. 78-82.
Chantler, I., D. Mitchell, and A. Fuller, Diclofenac potassium attenuates dysmenorrhea and restores exercise performance in women with primary dysmenorrhea. J Pain, 2009. 10(2): p. 191-200.
Rad, M., M.T. Sabzevary, and Z.M. Dehnavi, Factors associated with premenstrual syndrome in Female High School Students. J Educ HealthPromot, 2018. 7: p. 64.
Cheng, S.H., et al., Factors associated with premenstrual syndrome – a survey of new female university students. Kaohsiung J Med Sci,2013. 29(2): p. 100-5.
Fernández, M.D.M., et al., Premenstrual syndrome and alcohol consumption: a systematic review and meta-analysis. BMJ Open,2018. 8(3): p. e019490.
Bruinvels, G., et al., Prevalence and frequency of menstrual cycle symptoms are associated with women’s availability to train and compete: a study of 6812 exercising women recruited using the Strava exercise app. BritishJournal of Sports Medicine, 2020.