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Neuro Athletes, 

Not long ago I Tweeted about menstrual cycle tracking and sports performance, a central theme in my work as a sport neuroscientist and neurophysiologist.

Following was a barrage of nearly 350 comments and over 800 reactions to the post, although only the vast minority addressed the topic at hand. Most agreed and some were shocked and offended to the use of the phrase “he” insinuating that I did not take female coaches into consideration.

The truth is, I meant all coaches. Any coach who is training a female athlete should be fully

In 2015, former British no. 1 tennis player, Heather Watson, attributed her defeat in the Australian Open to her period, a statement that has given voice to the reality that periods do affect female athletes’ training and performance negatively: from physiological impacts like heavy menstrual bleeding, severe pain, and reduced energy levels, to psychological impacts like lack of motivation, fluctuating emotions, and anxiety.

Considering this an issue as a means to maximize their performance, the U.S. female soccer team became one of the first sports teams to factor the menstrual cycle into their player’s training needs. They tracked each player’s menstrual cycle and built individualized training loads and diets accordingly. This approach has contributed to their victory and success in defending their world cup title in 2019 (Smith, 2019). 

For many years, athletes have understood the impact of recovery, hydration, and nutrition on their athletic performance and work their training approach around them. However, these understandings often stem from research that studies more men (61%) than women (39%) (Costello et al., 2014), thus making the average evidence-based training protocols more tailored to men’s physiology rather than women’s (McGroarty et al., 2020; Emmonds et al., 2019). This approach may not be ideal in terms of maximizing the performance of female athletes as it was evident that the menstrual cycle strongly affects the physiological and psychological aspects of women.  

The flaws in this approach could also be seen from the higher rate and severity of reported sustained injuries like concussions (Covassin et al., 2016) and anterior crucial ligament ruptures (Ireland, 2002) in female athletes as compared to their male counterparts. Growing evidence has indicated that these differences are linked to the hormonal changes occurring in females during the menstrual cycle. 

The Menstrual Cycle 

The two primary reproductive hormones in females are estrogen and progesterone. Unlike the male hormone (testosterone), which appears to be more stable, the female hormones fluctuate in a predictable pattern throughout the menstrual cycle that typically lasts for approximately 28 days (Patricio & Sergio, 2019). 

In general, the menstrual cycle comprises four phases:

• Phase 1 (menstruation phase or early follicular phase) starts with the first day of the period and lasts for about a week. During this phase, the wall of the uterine (endometrium) sheds, and the levels of estrogen and progesterone are at the lowest. 

• Phase 2 (late follicular phase) typically occurs in the second week of the cycle. At this phase, the estrogen level increases while the progesterone level remains low. 

• Phase 3 (ovulation phase) usually occurs around the 14th day of the cycle. During this phase, the level of estrogen is at its peak while the progesterone remains low. 

• Phase 4 (luteal phase) begins right after the ovulation phase. At this stage, the estrogen and progesterone levels elevate to support the thickening of the endometrium. However, if pregnancy fails to occur, these hormone levels decrease and reach their nadir by the fourth week (late luteal phase), and the cycle restarts. 

Importance Of Adapting The Training Needs Of The Menstrual Cycle

Beyond their roles of sex hormones, estrogen and progesterone, which circulate in the blood, can affect the functions of the other parts of the body including the ability to train and recover, level of motivation, and susceptibility to injuries. 

Training and Recovery 

Muscle damage, a common phenomenon that occurs in athletes after an intense training session, is characterized by muscle soreness and loss of strength (Kendall & Eston, 2002; Tiidus, 2016). At the tissue level, muscle damage is followed by increased muscle inflammation, and subsequently, muscle repair. 

It is well-documented that estrogen reduces muscle damage by stabilizing the muscle membrane and decreasing its susceptibility to muscle disruption (Tiidus, 2016). Furthermore, estrogen enhances muscle repair by reducing inflammation and intensifying the activation and proliferation of muscle satellite cells, which are crucial for muscle regeneration (Kendall & Eston, 2002; Tiidus, 2016). 

In a meta-analysis (Romero et al., 2021), female athletes who exercised in between the late follicular phase and mid-luteal phase of the menstrual cycle (when estrogen or progesterone levels are high) reported lesser soreness and loss of strength. On the contrary, athletes who exercised when they were at the early menstruation phase of the menstrual cycle (when estrogen and progesterone levels are low) experienced more soreness and loss of strength. 

These findings indicate that the high estrogen levels during the late follicular phase to the mid-luteal phase may shorten the recovery period after an intense workout. As such, Romero et al. (2021) suggested that increasing loads during the late follicular phase and mid-luteal phase, and incorporating recovery periods during the early follicular phase can be beneficial for female athletes.

Motivation Level And Performance

Besides its protective role on skeletal muscles, estrogen elevates mood and emotional states in women by increasing serotonin levels (a neurotransmitter that affects mood) and serotonin receptors in the brain (Del Río et al., 2018). 

A literature review on the impact of the menstrual cycle phase on athletes’ performance revealed that female athletes commonly perceived performance to be worse during the early follicular and late luteal phases due to the experiencing of symptoms like fatigue or lethargy (Carmichael et al., 2021). Notably, this coincides with the low levels of estrogen and progesterone during these phases. 

On a different note, Oosthuyse et al. (2005) found that female athletes were able to clock a faster finishing time when compared to other phases during a cycling time trial. Similarly, Cook et al. (2018) showed that elite female athletes demonstrated higher anaerobic performance during the ovulatory phase in which estrogen levels are at their peak. The authors also reported that the athletes’ motivation to train and compete was greatest at this phase. 

Due to the increase in motivation and the speed of recovery associated with the high estrogen level during the late follicular and ovulation phase, structuring an intense workout during these menstrual cycle phases will thus allow the individual athletes to push through their workouts and optimize their training session.

Susceptibility To Injury 

In contrast to how estrogen exhibits a strengthening effect on the skeletal muscles, estrogen decreases the stiffness of the ligaments and tendons (collectively referred to as sinew). The increase in laxity of the sinews is believed to be associated with the higher ACL ruptures observed in female athletes compared to their male counterparts. 

One study in 1998 attempted to link the incidence rate of ACL in women to the menstrual cycle phase (Wojtys et al., 1998). The authors found that women had a higher incidence rate of ACL during the ovulatory phase of the menstrual cycle when estrogen level surges. This pattern appears consistent in later studies (Wojtys et al., 2002; Beynnon et al., 2006; Adachi et al., 2008; Martin et al., 2021) 

Besides ACL injuries, the National Collegiate Athletic Association Injury Surveillance Program reported that females had 1.4 times higher overall concussion injury rates than males in the same sports (Covassin et al., 2016). Moreover, female concussed athletes took longer to recover from their concussion than did male concussed athletes. 

Interestingly, a different study showed that women who experienced a concussion during their luteal phase appear to suffer worse post-concussion syndromes like headache, nausea, dizziness, and trouble concentrating than those who had concussions during other menstrual cycle phases (Wunderle et al., 2014). 

While the exact cause is still unclear, the findings from these studies have suggested that the menstrual cycle can be predictive of the risk and severity of the sports-induced injury and hence, allows better management of the injuries in female athletes. 

Closing Thoughts…

The physiology and psychology of women are heavily affected by the menstrual cycle, during which the primary sex hormones fluctuate in a predictable pattern throughout a 28-day cycle. Hence, understanding the menstrual cycle and adapting the training to the individual’s cycle is crucial to maximizing the performance of female athletes. 

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