MENSTRUAL CYCLE: PRACTICAL CONSIDERATIONS FOR THE TEAM PHYSICIAN

Introduction

The female athlete faces a changing hormonal milieu thorough the menstrual cycle. The reproductive hormones have an impact on several physiological systems and may influence training adaptions, performance, recovery, and injury risk.

It is still unclear the direction and magnitude of these effects in the different phases of the menstrual cycle. Research about this topic is limited and the menstrual cycle is frequently considered a barrier to include female athletes in sports performance studies1-4. In the scarce literature available, the methodological quality is generally low, and the results are often conflicting5-6

Due to the large variation of the hormonal profile during the menstrual cycle between athletes, and within the same athlete on different cycles, monitoring cycle phases and symptoms is paramount to develop a tailored strategy.

The focus of this article is the eumenorrheic athlete, with a menstrual cycle length between 21 and 35 days, with 9 or more consecutive periods per year7. The use of

Menstrual Cycle

hormonal contraception and its relation to performance and injury risk will not be reviewed8

The menstrual cycle

The menstrual cycle is a biological rhythm that prepares the female reproductive tract for pregnancy and is the result of an interaction between hypothalamic, hypophyseal and ovarian hormones9. There are estrogen and progesterone fluctuations along each cycle, that normally last for 28 days on average (range 21 to 35 days)2, 10, 11

There are two main phases, the follicular phase, and the luteal phase. These phases are separated by ovulation when an egg is released from the ovary. The cycle can be further divided 3, 5, 6 or 7 phases. In the 6-phase cycle one can consider: early follicular (menstrual phase), late follicular, ovulation, early luteal, mid-luteal and late luteal (premenstrual phase) phases. In Figure

1 a 28-day eumenorrheic cycle is represented. The follicular phase begins with the first day of menses (day 1-5) and both estrogen and progesterone are low. Estrogen increases steadily and peaks just before ovulation (12 to 14 days after menstruation onset) and then it starts to decline. In late follicular phase, estrogen levels are high and progesterone levels are low. After ovulation, the luteal phase begins and there is a gradual increase in progesterone levels. In the mid-luteal phase estrogen levels also increase, resulting in high levels of both hormones in this phase. Both hormones’ levels start to decrease in the late luteal phase, resulting on low levels of estrogen and progesterone in the premenstrual phase10

The female steroids have numerous effects on body systems12,9. Estrogen has anabolic and neuroexcitatory effect and decreases connective tissue stiffness. Progesterone has antiestrogen effect, with a catabolic and neuroinhibitory effect. In addition, progesterone also has thermogenic and hyperventilation effects2,9-12. The interplay of these hormones can be synergistic, antagonistic, or interactive on sports performance9

In terms of hormone levels, the cycle has 3 distinct patterns: low estrogen and progesterone (early follicular phase), high estrogen and low progesterone (ovulation) and high estrogen and progesterone (mid luteal phase)3

How to determine menstrual cycle phase

The calendar-based counting method is useful to predict menstruation, but bleeding does not confirm that an ovulation has occurred, nor it excludes luteal phase deficiency. These abnormalities are more common in heavy exercisers, so this can occur more often in asymptomatic elite sports women than in general population.

Basal body temperature measurement relies on the fact that after ovulation there is an increase in basal body temperature of 0.30.6o Celsius3,13 due to the rise of progesterone and its thermogenic effect. This temperature peak can be a surrogate that ovulation has occurred, although it does not inform of the actual progesterone level. Several factors can influence basal body temperature readings such as stress, sleep disturbances, illness, and other environmental factors, so this method is not recommended3. Urinary LH measurements allows us to determine the peak of this hormone and it’s known that ovulation usually occurs within 14-26 hours of the LH peak.

Unquestionably, serum hormone analysis is the gold standard to establish the actual levels of each hormone at a certain time. Assessment of progesterone level at mid-luteal phase allows us to confirm an anovulatory or a luteal phase deficiency cycle, if the level falls below a cutoff value. In the research setting, including these athletes in the analysis will lead to confounding results, therefore this should be used an exclusion criterion for such studies3

Salivary hormone measurements may need several samples collected during the day to achieve reliable results due the pulsatile pattern of salivary estrogen3

Menstrual Cycle symptoms

Abdominal pain/distension

Headache

Back pain

Fatigue

Nausea/vomiting

Hot flashes

Breast tenderness

Muscle aches

Dizziness

Swelling

Table 1: Adapted from the Menstrual Distress Questionnaire 15

To improve the methodological quality of research, a more robust phase verification is needed so combination of methods should be used. A 3-step method is recommended 14: a calendarbased counting, plus urinary LH surge detection kit, plus progesterone measurement at the luteal phase. This will allow us to confirm that the woman is at the luteal phase. Other phases can be established from this assumption and further confirmed with serum estrogen measurements 3,7,14

Sleep disturbances

Difficulty concentrating

Forgetfulness

Anxiety

Irritability

Mood swings

Restlessness

Crying

Restlessness

Food craving

Cycle and symptoms tracking A menstrual status, menstrual loss flow, and symptoms diary should be encouraged. Severity of symptoms and measures of wellness/readiness to train should also be recorded. A nonexhaustive list of symptoms is presented in Table 115. Symptom intensity can be assessed with a Likert scale (e.g., 1 - “no experience of symptoms” to 6 -” disabling symptom”).

Athletes should be aware of their menstrual cycle phases and how they feel across the cycle, especially in the more symptomatic phases such as the premenstrual and menstrual phases (late luteal and early follicular, respectively). This will allow practitioners to develop an individualized management strategy, namely, adjusting training, rest, nutrition, and pharmacological interventions when needed, to promote physical and mental wellbeing and readiness to train1

Female athletes should feel at ease to discuss any menstrual cycle related topic with their medical team. Talking about menstruation, premenstrual syndrome, period cramps should be normalized, like any other health issue1

The coaching staff should have a basic knowledge about the topic as this is a variable than can impact the player’s wellbeing and performance.

The menstrual cycle and performance

In a metanalysis performance was trivially reduced during early follicular phase compared to other phases5. The low estrogen and progesterone levels in menstrual phase could eventually hinder performance but this has not been confirmed by other recent reviews11, 13, 16

In terms of strength performance, a metanalysis only found non-significant trivial to small differences among phases in the studies outcomes10

Menstrual Cycle and Performance

Due the poor quality of the studies, large variation among studies and the trivial effect size, no guidelines could be formulated at this time.

The most frequent comparison is between the early follicular phase (both hormones are low) with the mid-luteal phase (both hormones are high). However, comparing early follicular with late follicular is also important as it could test the unopposed effect of

Menstrual Cycle and Injuries Incidence

Wojtys 1998 Wojtys 2002 Beynnon 2006 Adachi 2008 Ruedel 2009 Martin 2021 estrogen on performance (pre-ovulation).

Negative symptoms such as pain and fatigue are more common around the pre-menstrual and menstrual phases (late luteal and early follicular) and are perceived by the athletes to be detrimental to their performance [11]. Athletes perceived that their performance is at its best around ovulation and at its worst at early follicular and late luteal but these finding do not align with the objectively measured performance outcomes11,17

The menstrual cycle and injuries

Limited evidence shows two peaks of injury incidence (namely ACL tears), around ovulation and late luteal/early follicular, but it does not suffice to recommend changing risk mitigation practices along the menstrual cycle 6

Around ovulation, estrogen levels are higher and unopposed by progesterone (that is low). Estrogen decreases stiffness of tendons and ligaments and that could make female athlete more prone to injuries during this phase 18. Nonetheless, this has not been confirmed by the latest reviews that had a special focus on ACL injuries 19,20. A recent study with elite footballers found that muscle and tendon injuries occurred twice more frequently in late follicular in comparison to early follicular and luteal phase 21. However, this study relied on self-reported cycle length (calendarbased method) to determine the menstrual cycles phases, so the findings must be interpreted with caution. More studies are needed to make guidelines regarding injury risk management across the menstrual cycle 22. Sports injuries are a complex phenomenon and result of the interaction of several risk factors and possibly female steroids hormone levels could be one of them 23. Other factors related to the female sex and gender, unrelated to hormone profile, such as environmental aspects, could play a key role 24

The menstrual cycle and training

Phased-based resistance training to maximize adaption (e.g., taking advantage of the anabolic effect of estrogen) is potentially promising, but evidence is poor and inconsistent 25

Two recent reviews analysed longterm adaptation to resistance training across the menstrual cycle, but the methodological flaws of the studies included limit the conclusions 25,26. One review concluded that the symptoms of DOMS and strength loss were lower in the mid-luteal phase in comparison with early follicular phase, so higher training load could be recommended at that phase 25. In the other review, some studies found follicular phase training to be superior to luteal and regular training (training on both phases) 26. Unfortunately, the low quality of the studies limits the application of the findings. The current evidence is insufficient to warrant a general recommendation on resistance training according to the menstrual cycle phase.

Conclusions

Periodising training and injury prevention programs based on the menstrual cycle phase had limited evidence. Further high-quality research is needed, namely in comprehensive menstrual cycle phase detection methods. Nonetheless, menstrual cycle monitoring and symptoms tracking is recommended to adjust training and other strategies to promote to wellbeing and readiness to perform in the most symptomatic phases.

Players should be encouraged to improve their knowledge and awareness about their menstrual cycle phase and its relation to sports performance and wellness.

Due to the large variability of the menstrual cycle between players and within player, an individualised approach is currently recommended.

References

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