Dr Tess Flood
Department of Sport and Exercise Science, Institute of Sport,
Manchester Metropolitan University, UK

Professor Kirsty Elliott-Sale
Department of Sport and Exercise Science, Institute of Sport,
Manchester Metropolitan University, UK

The eumenorrheic menstrual cycle is an important biological rhythm in cis-gendered sportswomen not taking hormonal contraceptives. The cycle is regulated by the hypothalamic-pituitary-ovarian axis and is characterised by large fluctuations in the key ovarian hormones oestrogen and progesterone. These fluctuations are predictable and can be used to create distinct phases of the cycle that make up the eumenorrheic hormonal profile.

Phases of the menstrual cycle

A eumenorrheic menstrual cycle has a cycle length of of between 21 and 25 days. Historically, the menstrual cycle was broken down into two main phases – follicular and luteal – that were split by ovulation. Currently the menstrual cycle is divided into four phases, which have distinct hormonal concentrations (Fig.1, Phases 1 – 4).

Physiology of the menstrual cycle

The menstrual cycle is a reproductive cycle; at the beginning follicle stimulating hormone and luteinising hormone stimulate follicle maturation and oestrogen production. The increase in oestrogen – via positive feedback – causes a surge in luteinising hormone, which triggers ovulation and the release of a mature egg. A corpus luteum forms, which secretes large quantities of oestrogen and progesterone and subsequently increases cervical mucus. If fertilisation does not occur the corpus luteum regresses, ovarian hormone levels decrease, the egg passes through the uterus, and the endometrium lining sheds, and the next cycle begins.

Menstrual cycle dysfunction

Menstrual dysfunction can occur due to numerous reasons (i.e. illness or disease, low energy availability, first two years of menses, before menopause) (Elliott-Sale et al., 2021) and can result in the conditions shown in Fig.2. Amenorrhea or the loss of menstruation is the most publicised [by the media] type of dysfunction; however, sub-clinical dysfunction can also occur and include luteal phase deficiency (LPD, suppressed progesterone at Phase 4) and anovulatory cycles (no ovulation, suppressed oestrogen and luteinising hormone surge) (Allaway et al., 2016). Clinical dysfunction such as oligomenorrhea (inconsistent intermenstrual intervals and hormonal characteristics) and amenorrhea (loss of menstruation) are much easier to detect as they result in noticeable changes in a women’s cyclic pattern (Allaway et al., 2016).

It is worth stating that, outside of menstrual dysfunction, the menstrual cycle can also be perturbed by pregnancy, menopause, and hormonal contraceptives; please note that this list is not exhaustive. Although these profiles are outside of the scope of this article, in brief they represent elevated (i.e. pregnancy), depressed (menopause) and exogenous (hormonal contraceptives) hormonal profiles.

Quantity of research

To date 6% of the research in sport and exercise science has been conducted exclusively on women. Within this 6%, 20% of the research has focused on sex-specific topics such as the menstrual cycle or hormonal contraceptives. Women account for approximately 34% of the participants studied between 2014 and 2020 when mixed-sex studies are included (Cowley et al., 2021). In the most recent review of the effect of menstrual cycle on exercise performance, 78 studies were included with a total of 1193 participants (McNulty et al., 2020). However, in a review of the biomechanical surrogates for anterior cruciate ligament (ACL) risk and ovarian hormones, only 7 studies were included in the review totalling 194 participants (Dos’Santos et al., 2023). In addition, no studies assessing the menstrual cycle focus on elite women populations; instead, research is conducted in amateur and sub-elite populations assuming a linear relationship with elite women (Burden et al., 2021). These statistics highlight how little research is conducted on women and, as such, how limited our knowledge and understanding are about sportswomen and athletic performance. In the following sections, we have provided some examples of the outcome measures being investigated in relation to ovarian hormone profile; however, we acknowledge that this list is not exhaustive.

Perception and symptoms

From a sample of 1,086 non-hormonal contraceptive-using athletes across 57 sports, approximately 78% of them [self] reported experiencing menstrual cycle symptoms (Ekenros et al., 2022). The most common symptoms were breast tenderness, bloating, irritability, fatigue, loss of energy, and tearfulness. Often, these symptoms were perceived to impact women’s athletic performance; women on average perceived a negative impact on aspects of physical performance during the early follicular phase (during menses) and the late luteal phase (in the days prior to menses) compared to the ovulatory phase (mid-cycle) of the menstrual cycle (Ekenros et al., 2022).

Athletic performance

In a recent meta-analysis, performance was trivially reduced in Phase 1 compared with the other phases of the cycle (McNulty et al., 2020); however, this response was highly variable between studies. This meta-analysis included studies using laboratory-based assessments of endurance and acute strength performance. As such, the authors concluded that at present an individualised approach should be adopted until a sufficient high-quality dataset is available. The impact of “trivial effects” in elite sportswomen is unknown; it could be suggested that the impact will be of greater relevance to elite sportswomen where the margins in performance are smaller or conversely the impact could be of less relevance to elite sportswomen as they can be more resilient to adverse conditions and the size of the effect could be lost amongst other competitive factors. In all cases, an individualised approach is recommended for women, where the menstrual cycle is tracked and any alterations to training are tailored to and informed by the individual athlete and/ or their data.

Strength adaptations

Acute and chronic strength changes have been suggested to occur across the menstrual cycle. A recent umbrella review paper (Colenso-Semple et al., 2023) examined and critically evaluated the reviews on menstrual cycle and strength outcomes (acute and chronic). The study showed largely inconsistent evidence of differences in strength and hypertrophy outcomes with changes in ovarian hormones. Therefore, the authors concluded that, at the present time, it is highly premature to conclude that short-term fluctuations in ovarian hormones over a menstrual cycle influence acute strength or longer-term adaptations to resistance training. It was also suggested that “phase-based” training models are not an evidence-based approach.

Substrate utilisation

There is currently conflicting evidence on whether changes in oestrogen through the menstrual cycle impact substrate utilisation (i.e. carbohydrate and fat utilisation during exercise) (Boisseau and Isacco, 2022). While some studies have shown that increased oestrogen at Phase 2/4 promoted greater fat oxidation rates, others have not replicated these findings. This could have occurred due to differences in energy demands between studies (e.g. increased energy demand, increased endogenous glucose production). It is also postulated that inter-individual differences in magnitude of change in oestrogen could have influenced the impact on substrate utilisation (Oosthuyse et al., 2022). In the studies demonstrating an effect, it was hypothesised that increases in oestrogen concentrations promoted greater muscle glycogen synthase activity that led to greater glycogen storage and sparing during exercise and a reliance on fat utilisation.

ACL injury

Sportswomen are ~3.5 times more likely to suffer an ACL injury than men [depending on sport] (Dos’Santos et al., 2023). While ACL injuries are multi-factorial, it has been suggested that changes in ovarian hormone concentration throughout the menstrual cycle could potentially increase the susceptibility to ACL injury. However, at the current time research is inconclusive whether increased oestrogen levels predispose eumenorrheic sportswomen to greater ACL injury risk. Whilst some research has shown greater knee laxity in Phase 2 associated with increased oestrogen concentrations, evidence hasn’t linked this to ACL injury (Moriceau et al., 2022). It has been suggested that increased oestrogen (Phase 2) may influence soft tissue compliance, collagen formation, properties, and integrity of ligaments, knee laxity and neuromuscular function (Dos’Santos et al., 2023). In addition, a review examining biomechanical and neuromuscular injury risk surrogates showed no evidence to suggest elevated risk across the menstrual cycle (Dos’Santos et al., 2023).

Quality of the research

As well as a lack of research in sportswomen, the quality of research assessing ovarian hormones and athletic performance is poor. In McNulty et al., (2020) 78 papers were included in the meta-analysis; of these, 8% were rated high, 24% medium, 42% low, and 26% very low quality. In this paper considerations were taken of the methods used to identify and verify the menstrual cycle phase (and subsequent change in ovarian hormones) in the included studies. In Dos’Santos et al. (2023), all studies in the review were rated as low (n = 3/7) and very low quality (n = 4/7) using the methodology from McNulty et al., (2020). Table 1 highlights some of the methodological issues highlighted by these reviews.

Research containing these methodological issues could, for example, be including women who experience menstrual dysfunction (anovulatory or LPD) with eumenorrheic women. Therefore, these papers are not assessing the same fluctuation in ovarian hormones that are seen in an eumenorrheic profile; Fig.3 presents a graphical representation of this. Verifying ovarian hormone profiles in women is key to the trustworthiness of the result of the study (McNulty et al., 2020).

In 2021, methodological recommendations for testing women across the menstrual cycle were developed (Elliott-Sale et al., 2021). This paper provided a consensus on the hormonal profiles of interest and the a priori guidelines for eligible data. Fig.4 summarises the recommendations for research designs assessing the impact of ovarian hormones on athletic performance (Elliott-Sale et al., 2021).

Summary and take-home messages

Before any conclusions are drawn about the impact of ovarian hormone concentrations and the menstrual cycle on athletic performance, more high-quality research is needed on these topics in both amateur and elite populations. By including recent recommendations into future research, robust guidance will be able to be created for sportswomen. At the moment evidence suggests an individualised approach, which is tailored to and informed by the athlete’s experiences. At the current time it is highly premature to make firm conclusions on the impact of ovarian hormones and the menstrual cycle on athletic performance based on the available research evidence.

References

Allaway HCM et al. (2016). The physiology of functional hypothalamic amenorrhea associated with energy deficiency in exercising women and in women with anorexia nervosa. Hormone Molecular Biology and Clinical Investigation 25(2), 91–119. https://doi. org/10.1515/hmbci-2015-0053.

Boisseau N, Isacco L (2022). Substrate metabolism during exercise: Sexual dimorphism and women’s specificities. European Journal of Sport Science 22(5), 672–683. https://doi.org/10.1080/17461391.202 1.1943713.

Burden RJ et al. (2021). Elite female athlete research: stop searching for the “magic P”. Experimental Physiology 106(10), 2029–2030. https://doi. org/10.1113/EP089884.

Colenso-Semple LM et al. (2023). Current evidence shows no influence of women’s menstrual cycle phase on acute strength performance or adaptations to resistance exercise training. Frontiers in Sports and Active Living 5. https://doi.org/10.3389/ fspor.2023.1054542.

Cowley ES et al. (2021). “Invisible sportswomen”: the sex data gap in sport and exercise science research. Women in Sport and Physical Activity Journal 29(2), 146–151. https://doi.org/10.1123/ WSPAJ.2021-0028.

Dos’Santos T et al. (2023). Effects of the menstrual cycle phase on anterior cruciate ligament neuromuscular and biomechanical injury risk surrogates in eumenorrheic and naturally menstruating women: A systematic review. PloS One 18(1), p. e0280800. https://doi. org/10.1371/journal.pone.0280800.

Ekenros L et al. (2022). Perceived impact of the menstrual cycle and hormonal contraceptives on physical exercise and performance in 1.086 athletes from 57 sports, Frontiers in Physiology 13, 954760. https://doi.org/10.3389/fphys.2022.954760.

Elliott-Sale KJ et al. (2020). The effects of oral contraceptives on exercise performance in women: a systematic review and meta-analysis. Sports Medicine 50, 1785–1812. https://doi.org/10.1007/s40279- 020-01317-5.

Elliott-Sale KJ et al. (2021). Methodological considerations for studies in sport and exercise science with women as participants: a working guide for standards of practice for research on women. Sports Medicine 51(5), 843–861. https://doi.org/10.1007/ s40279-021-01435-8.

Langan-Evans C et al. (2023). Hormonal contraceptive use. menstrual cycle characteristics and training/ nutrition related profiles of elite, sub-elite and amateur athletes and exercisers: One size is unlikely to fit all. International Journal of Sports Science and Coaching [Preprint]. https://doi. org/10.1177/17479541231163088.

McNulty KL et al. (2020). The effects of menstrual cycle phase on exercise performance in eumenorrheic women: a systematic review and meta-analysis. Sports Medicine [Preprint], (0123456789). https://doi. org/10.1007/s40279-020-01319-3.

Moriceau J et al. (2022). The influence of the menstrual cycle and oral contraceptives on knee laxity or anterior cruciate ligament injury risk: a systematic review. Applied Sciences 12(24), 12627. https://doi. org/10.3390/app122412627.

Oosthuyse T et al. (2022). Understanding the female athlete: molecular mechanisms underpinning menstrual phase differences in exercise metabolism. European Journal of Applied Physiology [Preprint]. https://doi. org/10.1007/s00421-022-05090-3.