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The period problem: does menstruation make females more vulnerable to injury?
Because menstruation is the visible sign of the female reproductive cycle, it’s natural to assume women should take it easy during this time. However, new research calls this thinking into question. Jasmine Marcus explores the topic and suggests that ovulation, not menstruation, may put athletes at a higher injury risk.
More and more young girls are encouraged to play sport. Many of them continue to pursue active and competitive lifestyles through adulthood. For instance, nearly half of the athletes expected to participate in the 2020 summer Olympics (held in 2021) are women(1). Yet, researchers have largely ignored the question of how the menstrual cycle affects performance and injury rates.
The menstrual cycle
A typical menstrual cycle for women (who are not taking hormonal birth control (HBC)) lasts 21-34 days. Each cycle starts with the first day of menstruation and lasts until the first day of the next period. There is much variability in period cycles depending on hormonal levels, the use of HBC, and the athlete’s age.
Ovulation, the moment the ovaries release an egg, occurs mid-cycle and divides the cycle into phases. The follicular phase comes before ovulation, and the luteal phase occurs after (see figure 1). The late follicular phase starts three day preceding ovulation and extends through ovulation. Estrogen levels build during the follicular phase and peak during the late follicular phase at amounts nearly 10 times higher than at the start of the cycle.
Figure 1: The menstrual cycle and hormonal fluctuations*
*Adapted from a graphic created by Dr Laura Bowen, lead women’s and girls’ sport scientist at Southampton FC. Used with permission from Women’s Soccer Coaching. 2021 Feb;03:9.
An oft-quoted Swedish study found soccer players at a higher risk of injury while menstruating(2). This study was methodologically flawed and did not define the menstrual cycle’s phases or differentiate between different types of injuries(3). Therefore, to study the effect of menstrual cycles on injury, scientists in the UK followed nearly 4,000 elite female soccer players (aged 13-35) for over four years. They defined injury as an event that prevented a player from participating in a game or practice for at least one day. They excluded those with absent or irregular cycles and those taking HBC from the study. The athletes reported their menstrual cycles, and the researchers estimated ovulation based on the timing. They then divided each cycle into the follicular, late follicular, and luteal phases.
The study found 156 injuries in 113 athletes. When evaluating the incidence of injury during the follicular phase, researchers observed nearly twice as many injuries in the late follicular period as in the early part of the follicular phase. Also, incidents occurred in the late follicular phase 32% more often than in the luteal phase. Thus, the subjects in this study appeared more vulnerable to injury during the time just before ovulation. Interestingly, muscle and tendon injuries were twice as likely to happen during this time.
Even though 20% of the injuries occurred in a prolonged luteal phase while waiting for an overdue period to start, it seems that it’s not menstrual dysfunction but regular menstrual cycles that increase times of vulnerability in athletes. Estrogen peaks during the late follicular phase, and some suggest that it reduces ligament and increases tendon stiffness(3). However, more research is necessary to reach conclusions about the impact of hormonal shifts on tissue resilience. Furthermore, scientists must tease out how factors influenced by hormonal fluctuations such as sleep, fatigue, appetite, and mood affect an athlete’s performance, reflexes, and motor control.
A late or absent period in an athlete without pregnancy or other medical condition can be a sign of Relative Energy Deficiency in Sport (RED-S), an expansion of the female athlete triad. This condition occurs when an athlete doesn’t consume enough calories to meet their energy demands, resulting in low energy availability.
Although more common in female elite and aesthetic sport athletes, RED-S can occur in anyone, regardless of sex or performance level. The loss or interruption of the menstrual cycle can have significant consequences for athletes. Twenty percent of the injuries suffered by the athletes in the UK study occurred during a prolonged luteal phase. Roughly one-third of these were joint and ligament injuries; however, prolonged amenorrhea also decreases bone density and increases the athlete’s chances of experiencing a bone stress injury. Left untreated, RED-S impacts performance and the athlete’s overall health.
Other causes of injury
The menstrual cycle’s hormonal fluctuations are only one of a multitude of factors that affect performance and injury. There is a tendency to blame female athlete injuries on biology(4). However, sex (physical and physiological characteristics) and gender (societal identities, roles, and structures) are often entangled.
For instance, strength training can mitigate injury risk. Yet, many women encounter barriers to taking advantage of this aspect of training. Female athletes often aren’t encouraged or provided with the same resources to strength train as their male counterparts. One viral example of this was the disparity in training rooms set up for the 2021 NCAA men’s and women’s basketball tournaments(5). While the men were provided with a fully equipped weight training room, the women were given a single rack of dumbbells that didn’t go above 30 pounds.
But, even when given access to the same resources, societal pressures to look feminine and a less than welcoming culture in the training room may discourage female athletes from taking full advantage of strength training. Factors such as these play a role in injury rates but are harder to account for in research. While it will always be challenging to isolate the impact of sex on injury rates, it’s important to recognize and account for these issues in future studies.
While the UK study is a great start, there is not enough research on the menstrual cycle and its effect on athletes to influence training decisions. However, there are still several takeaways for athletes and sports injury professionals.
Encourage athletes to track their menstrual cycles. The American College of Obstetricians and Gynecologists refers to the menstrual cycle as a vital sign and says monitoring it can alert people to changes or irregularities that might require medical attention. Knowing the rhythms of their cycle allows athletes to recognize if their period is late or becomes irregular. They should discuss any irregularities with their medical providers.
Knowledge of their ovulation gives athletes insight into their physical, emotional, and mental acuity and helps them plan their training phases accordingly. Athletes and clinicians can compare the data from their menstrual cycle to their training logs and note any patterns. For example, some athletes report feeling tired when menstruating, while others notice more aches and pains near ovulation. If a clear relationship emerges, the athlete may wish to structure their training or rehabilitation around their cycle in coordination with their coach or providers.
Rehabilitation professionals should include questions about the menstrual cycle in every intake history. Physios may be the first medical provider alerted to the signs of RED-S or other menstrual dysfunction. Be particularly concerned about athletes who’ve experienced long periods of amenorrhea or have repeated bone stress, tendon, or ligament injuries.
As females learn to understand their bodies better, they may appreciate your inquiry into the phase of their cycle and how it affects them. While there isn’t enough research to support changing rehab approaches based on menstruation, clinicians may have a more effective treatment session if sensitive to the subjective effects of the phases in the athlete’s cycle.
Since the different phases of the menstrual cycle are important, it is helpful to know how to determine the time of ovulation. There are several easy ways to track ovulatory cycles. Those with a regular and predictable cycle (and not using HBC) typically ovulate 14 days before the start of the following period. Physical symptoms that corroborate with the calendar include changes in cervical mucous, light cramping, and a change in morning basal body temperature. When ovulating, cervical mucous becomes more slippery, and basal body temperature rises 0.4-0.8 degrees Fahrenheit. Over-the-counter ovulation tests, which detect luteinizing hormone in urine, can also confirm ovulation. Several apps use cycle tracking data to estimate one’s period and ovulation. However, there are some privacy concerns with this method.
- https://movethelimit.com/women-in-sport-statistics-2020/; accessed 4/28/2021
- Medicine and Science in Sports and Exercise, 31 Mar 1989, 21(2):126-129
- Sports Act. Living, 01 March 2021. https://doi.org/10.3389/fspor.2021.616999
- Br J Sports Med 2021;0:1–8.
- https://ftw.usatoday.com/2021/03/ncaa-tournament-womens-weight-room-unequal-access;accessed 4/28/2021