With the professionalisation of female football, the demand for training and matches has significantly increased in the last years.^{1, 2} As a result, the overall injury rate is already similar to that of male football and the percentage of serious injuries is even higher.^{3, 4}

This brings about significant costs for clubs⁵ since female players have 21% more injury-related absences, mainly due to a higher incidence of severe knee and ankle ligament injuries. Anterior cruciate ligament (ACL) injuries, for example, occur 2-8 times more often in women.

Menstrual cycle may affect risk of injury

It has been hypothesised that the menstrual cycle may play a role in the risk of injury in female athletes, as cyclical fluctuations in reproductive hormones, such as oestrogen and progesterone (female sex hormones produced in the ovary that control menstrual cycles), can influence musculoskeletal tissues such as muscles, tendons and ligaments.^{6, 7}

Similarly, several studies have identified a higher risk of anterior cruciate ligament (ACL) injury in the follicular/late ovulatory phase when oestrogen concentrations are higher. However, other studies have shown a higher incidence of ACL injury during the early follicular or late luteal phase.

In any case, the impact of prolonged menstrual cycle length on injury risk had not been explored until 2021. That is when Dan Martin et. al. (2021) published the study “Injury Incidence Across the Menstrual Cycle in International Footballers”. The aim of the study was to assess how the phases of the menstrual cycle and the prolonged menstrual cycle length influenced the risk of injury in international female footballers.

Thus, understanding the different phases of the menstrual cycle is essential to understanding the study and its results.

The phases of the menstrual cycle

Menstruation is the shedding of the inner lining of the uterus (endometrium) and subsequent bleeding, usually lasting about 4 to 8 days. The first day of flowing is considered the start of the menstrual cycle, which ends just before the following period. A regular menstrual cycle lasts between 24 and 38 days.

Luteinising and follicle-stimulating hormones, produced by the pituitary gland (an inner-secreting gland at the base of the skull), regulate the menstrual cycle, promoting ovulation and stimulating the ovaries to produce oestrogen and progesterone.

Hence, the menstrual cycle has three phases: follicular phase (before the release of the egg), ovulatory phase (release of the egg) and luteal phase (after the release of the egg).

Follicular phase of menstruation

In the follicular phase of menstruation, oestrogen and progesterone levels are low, leading to the breakdown and subsequent shedding of the endometrium, which results in a period.

At that point, follicle-stimulating hormone levels increase, thus stimulating the development of follicles (in the ovaries) and, therefore, the eggs they contain. At the end of this phase, however, as the density of FSH decreases, typically only one follicle (called the dominant follicle) continues to grow. This remaining follicle then starts to produce oestrogen.

Ovulatory phase of menstruation

The ovulatory phase begins with an increase in the levels of luteinising hormones (which can be detected by a urine test) and follicle-stimulating hormones. Specifically, the latter stimulates the process of egg release, about 10 to 12 hours after the increase in LH.

Luteal phase of menstruation

In the luteal phase, the levels of luteinising and follicle-stimulating hormones fall. The follicle closes after releasing the egg and forms the corpus luteum, which begins to produce progesterone. Oestrogen levels are high at this stage, and progesterone and oestrogen cause further thickening of the endometrium, which begins to prepare for possible fertilisation. If this does not occur, the corpus luteum ages and stops producing progesterone, oestrogen levels decrease and endometrial shedding begins, leading to bleeding and the start of the new menstrual cycle.

Categories of the menstrual cycle for research purposes

The follicular phase was defined as the time between the first day of the last period and the late follicular phase.

Based on previous data,⁸ peak oestrogen concentrations were estimated to occur on the day of peak luteinising hormone and the two preceding days; this was called the late follicular phase.

The luteal phase was defined as any time after the late follicular phase.

Bases of the research

The Dan Martin et. al. (2021) study was conducted over 4 years. During that time (2012-2016), injuries to English international female footballers in training and matches were recorded, along with self-reported information on menstrual cycle characteristics at the time of injury.

Excluding criteria were pre-menarcheal players (who have not yet had their first menstrual period), hormonal contraceptive use, missing data from the last menstrual period, and irregular menstrual cycles.

Injury was defined as an event that prevents a player from participating in a training session or match for one or more days after the injury (Fuller et al., 2006). Injuries suffered outside of formal training and matches were excluded from the analysis.

Thus, injuries in eumenorrheic (normal menstruation) players were classified into early follicular, late follicular (ovulatory) and luteal phase. Frequencies were also compared between injuries recorded during a typical cycle and those occurring after the cycle was supposed to have ended.

Results: the impact of prolonged menstrual cycle length on injury risk

– Injury rates per 1,000 person-days were 31.9 in the follicular phase, 46.8 in the late follicular phase and 35.4 in the luteal phase.

– It was reported that 20% of the injuries occurred when the athletes’ periods were “late.”

– Compared to the follicular and luteal phases, muscle and tendon injuries were about twice as common during the late follicular phase, when oestrogen concentrations are higher.

– The potentially higher injury rate in the late follicular phase is consistent with some studies showing a higher rate of ACL injury during this phase.^{9, 10}

Conclusions

As the research points out, further studies are needed before clear guidelines on menstrual cycle phases and injury risk mitigation can be generated. The study does, however, serve as a basis for future research. It has also provided initial evidence that the risk of injury may indeed increase in typically eumenorrhoeic women in the days following the expected start of their next menstrual period. Thus, this research highlights the need to consider the menstrual cycle and menstrual dysfunction in athlete populations.

In fact, in line with other recommendations,^{11, 12} it is suggested that female football players keep track of their menstrual cycle length using tracking systems/apps, since a “late” period is easily identified and may present a greater risk to the athletes. In addition, the identification of prolonged cycles can facilitate discussion and rapport with appropriate support staff (that is, medical staff, nutritionists, psychologists, physiotherapists) to promote the female players’ health and well-being.

In this regard, according to Dr. Eva Ferrer, Specialist in women’s health and sport at Barça Innovation Hub, the important thing is to know the time of the menstrual cycle of each player: “If you don’t know at what phase each player is, it is of little use to know the theory to prevent injuries. FC Barcelona works to know correctly and scientifically at what time of the menstrual cycle the players may be in order to minimize these hormonal risk factors”.

Reference:

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