Menstrual cycle

Puberty and hormonal profile

From the onset of puberty (11^th – 15^th year) physiological and morphological changes between boys and girls occur. They are triggered by the influence of the sex steroid hormones, androgens (testosterone), progesterone and oestrogen (Knudtson & McLaughlin, update in 2019). Other hormones such as luteinizing hormone, follicle-stimulating hormone, and gonadotropin-releasing hormone, also play an important role in the sex-related areas and increases the physiology gap (Marques et al., 2018), picture 1.

Picture 1. HPG axis reproduced from MSD manuals.

Additionally, in girls, unlike boys, besides the influence of hormones on the body composition changes (body fat increase and accumulation in the hips’ and thighs’ area, widening of pelvis and hips, breasts grow), they are also responsible for the commencement of the first menstruation (menarche; 11-15^th year) (Knudtson & McLaughlin, update in 2019). 

Menstrual cycle 

The menstrual cycle (MC) – one of the most important signs of mankind – is influenced by daily fluctuation of ovarian hormones and occurs in women aged ¬ 11 to 50 years. The fairly consistent (and measurable) fluctuations of hormones across the MC divides the cycle into three main phases. The early follicular phase (1) which starts on the first day of menstruation and is characterised by low oestrogen and progesterone, the ovulatory phase (2), characterised by high oestrogen and progesterone (de Jonge et al., 2019), as depicted in the picture 2. The average length of what is considered a healthy MC lasts 21-36 days (McNulty et al., 2020; Constantini et al., 2005). The ‘textbook’  28 days cycle length occurs in only about 13% of women (McNulty et al., 2020). 

Picture 2. Menstrual cycle phases and hormonal changes adapted from Pitchers and Elliott-Sale, 2019.

Depending on the type of phase, performance, emotions – happiness, sadness, and love, appetite and libido or even bodily conditions like sleep and regeneration change accordingly (Sims, 2016). Furthermore, hormonal fluctuations during MC have been observed to particularly influence ventilation, thermoregulation, and substrate metabolism (Dombovy et al., 1987; Oosthuyse & Bosch, 2010). Additionally, the accompanying negative side-effects such as pain, heavy menstrual bleeding, anaemia, and mood changes have also been reported as common features accompanying the MC of many females (Bruinvels et al., 2016; Martin et al., 2018). 

Menstrual cycle and performance 

In regard to the female athletes, there are some proposed mechanisms by which the MC and the cyclical hormonal fluctuation might impact performance. Specifically, there have been some studies done both on animals and humans, which suggest that oestrogen might have an anabolic effect on skeletal muscle (Baltgalvis et al., 2010; Lowe et al., 2010) and has also been shown to play a role in substrate oxidation changes through increased muscle glycogen storage and increased fat utilisation (Boisseau and Isacco, 2021). On the contrary, progesterone is thought to have anti-oestrogenic effects (Frankovich and Lebrun, 2000). 

Moreover, some studies have reported improved performance outcomes during the early follicular (Campbell et al., 2001; Pallavi et al., 2017), ovulatory (Bambaeichi et al., 2004) and mid-luteal (Oosthuyse et al., 2005) phases; whereas others have shown no changes in exercise performance between MC phases (Casazza et al., 2002; de Jonge et al., 2001; de Jonge et al., 2012; Dibrezzo et al., 1988; Elliott-Sale et al., 2003; Mc La et al., 2007). Additionally, in terms of the specific training types, some studies have shown that strength training during follicular phase is more advantageous for building muscles when compared to luteal phase (Knowles et al., 2019; Sung et al., 2014; Wikstrӧm-Frisén et al., 2017). Presumably, it is influenced by the elevated levels of oestrogen and its anabolic effect on the skeletal muscles (Baltgalvis et al., 2010; Lowe et al., 2010). No such unequivocal findings were observed in endurance sports (de Jonge, 2003). 

Whilst it is plausible that changes in exercise performance might actually occur across different phase of the MC due to hormonal fluctuations (Ansdell et al., 2020; de Jonge, 2003; Frankovich & Lebrun, 2000; Lebrun, 1994; Lebrun et al., 2013), there is yet no unambiguous conclusion on the topic. Part of it might be affected by the difficulty to measure menstrual phases due to insufficient awareness of hormonal milieu (e.g., consideration of MC phase, type of HC used, stage of menopause) or inconsistence in the terminology describing the phases of MC, but also because of insufficient number of studies with adequate sample size discussing the MC cycle with a focus on athletes. Moreover, numerous elite athletes are known to be susceptible to menstrual irregularities, which disrupt their hormone profiles and thus make the interpretation of research finding even more challenging. Above all, however, the absence of evidence-based guidelines advising on the exercise performance across the MC for either exercising women or for practitioners and coaches working with elite sportswomen is perhaps the biggest and most demanded reason (Solli et al., 2020). 

Written by Tereza Hybská 

References 

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