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Hormonal Changes Affect Female Athletic Performance. Period.

Over the past year, several notable female athletes have publically discussed the impact of their menstrual cycles on athletic performance: at the 2016 Summer Olympics, a swimmer from China remarked that her race was impacted by having her period because she felt tired and weak; again at the Australian Open, a British tennis player cited “girl things” as a reason she was feeling fatigued during competition; and just last month USA gymnast Aly Raisman discussed the impact of her period on competition in a Cosmopolitan story after she participated in a string of advertisements for a brand of tampons geared toward female athletes.

While the stories caused a bit of a stir, with people questioning the validity of the claims, science may indicate that performance can be impacted by a woman’s menstrual cycle.  

“The bottom line is that hormonal shifts that drive the menstrual cycle can affect multiple parts of the body, including muscle, bone, endurance, energy level and attention,” said Ellen Casey, MD, CAQSM, FACSM, co-director of the Penn Center for the Female Athlete and an assistant professor of Physical Medicine & Rehabilitation and Orthopaedic Surgery. “Pain levels and pain perception can also change across the menstrual cycle, which may affect performance for some women.”

The Menstrual Cycle and Oral Contraceptives

It seems as though perceptions of performance changes for female athletes may be a bit more common that one might think. So common, in fact, some coaches and athletic trainers recommend female athletes use hormonal birth control, which they think can minimize the potential changes in performance by keeping hormones stable.

But, while hormone stabilization and predictable cycle length are common benefits of oral contraceptives, manipulating the menstrual cycles to avoid performance changes may have dangerous consequences such as the masking an underlying issue such as the Female Athlete Triad (more on that, later), and some studies show that certain types of might even worsen performance – and it’s not something that Casey and her team recommend. In fact, Casey and her colleagues at Penn who specialize in female athletes are working on understanding more about how these drugs interact with the body.

“Knowledge is power. Female athletes are already discussing the impact of periods on performance with their teammates, coaches, trainers. Unfortunately, there is not enough research in the area, which means there are lots of questions and not enough answers,” Casey said.  “However, as we learn more, I think a complete understanding of how women’s hormones and the hormones in birth control pills may be another area to consider when focusing on injury prevention and performance enhancement.”

Casey and colleagues at Penn Medicine and Northwestern University recently received grants from the American Academy of Physical Medicine and Rehabilitation and the National Institutes of Health to further explore the impact of oral contraceptives on the female musculoskeletal system.

“There are really two issues major challenges that we face as physicians treating active women. First is that there is a large amount of variability and uncertainty in how much hormones shift during the menstrual cycle for each woman – meaning some women can be more susceptible to changes driven by hormones because they have larger shifts in the concentration of hormones in the blood throughout the menstrual cycle. Second, all oral contraceptives prevent pregnancy equally as well, but there is a huge variety in how much hormones and what type each contain,” Casey added. “This uncertainty is, in part, due to the fact that most studies lump various types of oral contraceptives together, rather than focusing on pills with a similar hormonal profile.”

According to several studies, oral contraceptives with higher levels of male hormones may have a greater impact on athletic performance. It has also been shown that women taking birth control with higher levels of these hormones performed better in running and oxygen consumption (VO2max) — the amount of oxygen consumed during exercise, which is typically measured among elite athletes to evaluate aerobic fitness.  But, Casey said, “There were limited impacts on heart rate, endurance, or strength. So while it is thought that oral contraceptives stabilize hormones and improve athletic performance, there is still much to be evaluated in order to actually support this conclusion.”

Hormonal Changes and Injury Susceptibility

Oral contraceptives aside, the natural hormonal changes across the menstrual cycle can also play a larger role in the susceptibility of some sports injuries. While it might not seem that intuitive, common running injuries, like anterior cruciate ligament (ACL) tears and Runner’s knee, can occur more often during times of hormonal change.

Each muscle, tendon and ligament in the body has a receptor for estrogen, and during the menstrual cycle, the structure and function of these tissues change.  While it’s not entirely clear why these changes happen – something Casey and her team are exploring – there is a theory that as estrogen increases in the body, the ligaments and tendons loosen, which can cause instability in the knee. This may be a problem for athletes, like soccer players, who do a lot of stopping and starting, or cutting and landing during play. It’s also been found that during the menstrual cycle, women change the way they control their movements, which coupled with the tissue instability, can lead to injury.

During menstruation, many women struggle with muscle and joint pain, stiffness, and have decreased attention or energy levels – much like the Olympic swimmer and British tennis player. These symptoms may affect performance, but as Casey mentioned previously, how much of an impact it has is variable. 

“We also know that hormonal changes and the irregularity or absence of an athlete’s menstrual cycle can be an indicator of a much larger health concern for female athletes, the Female Athlete Triad,” said Kate Temme, MD, CAQSM, co-director of the Penn Center for the Female Athlete and an assistant professor of Physical Medicine & Rehabilitation and Orthopaedic Surgery.

The Triad is composed of three interrelated conditions including energy availability (nutritional intake), menstrual function and bone health. Temme added, “When athletes have insufficient nutrition to support the needs of both their sport and body’s physiological functions, their body goes into emergency shutdown mode. To save energy, many physiological functions are negatively affected, including bone growth, metabolism and reproductive function. Athletes with the Triad may have infrequent or absent menstrual cycles due to low estrogen levels, and they may also present with stress fractures because they lack sufficient estrogen to protect their bones.”

Ultimately, it’s important for sports medicine clinicians to feel comfortable asking athletes about their menstrual cycles, and for athletes to recognize that abnormal periods may require a visit to their health care provider for further evaluation. Understanding the link between nutrition, menstrual function and bone health will help to identify those athletes at risk for the Triad. One of the critical mistakes made when treating women with the Triad is to put them on oral contraceptives to compensate for low hormonal levels. Instead, treatment should focus on correcting the underlying low energy availability (insufficient nutrition) that caused the menstrual dysfunction. Oral contraceptives initiate menstrual bleeding even if underlying nutrition and hormones are still too low to support menstruation naturally. This makes it nearly impossible to know if women are recovering or still suffering from the Triad because they mask the underlying causes of infrequent menstrual cycles.

“Multi-disciplinary treatment programs are critical for successful treatment of the Triad and to prevent long-term health consequences including osteoporosis, infertility and effects on other organ systems,” Temme said. “The Triad is one of the areas Ellen and I are exploring in both the clinical and research setting. As with the work around oral contraceptives, there needs to be more scientific data addressing these unique female athlete concerns in order to better identify, treat, and ultimately prevent injury.”

The onus to change the way we look at and talk about menstruation and the impact of hormonal changes on the female athlete falls on physician-researchers, like Casey and Temme, to evaluate the implications of these changes; on professional athletes, like Aly Raisman, to speak candidly about these aspects of being a female athlete; and on the general population to become more open to these conversations and to break down stigma associated with public discussion of the impacts of a woman’s period.

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