In 2025, a FIFA-funded study aimed at studying the potential link between anterior cruciate ligament injuries in women and menstruation was launched at Kingston University. The study, led by PhD student Blake Rivers, will follow participants for four menstrual cycles, monitoring hormone levels while conducting biomechanical tests, including strength tests, 3D analyses, and electrophysiological analyses. “We are essentially observing all the major movements we believe pose the highest risk of injury without exposing participants to too much risk,” explains Blake Rivers. “The better we understand the interaction and what happens at the biomechanical level during these hormonal cycles, the more we can quantify the level of risk associated with this interaction.”
According to Blake Rivers, the two phases considered the most risky are those during which the most hormonal changes occur: the late follicular phase of ovulation and the intermediate luteal phase. He indicates that these phases are considered the most risky because estrogen, which affects ligament laxity, increases before ovulation, and progesterone, which “can have an impact on neuromuscular control and inhibition,” increases during the intermediate luteal phase. Blake Rivers and his co-director James Brouner hope to publish the results of their study by the end of 2026.
In parallel, the 2024 study by Emily Parker, a physical medicine and rehabilitation intern at MetroHealth in Ohio, also suggests that the intermediate luteal phase is the most risky. Emily Parker, who experienced tearing her left anterior cruciate ligament in high school, focuses on relaxin, a menstrual cycle hormone often associated with childbirth, as the main culprit. “Relaxin triggers menstruation by suppressing and breaking down collagen in the tissues around its receptors on the uterine wall,” she clarified via email. “These receptors are also found on women’s anterior cruciate ligaments, which draw attention to the luteal phase and their risks of knee injury. Estrogens amplify the effects of relaxin by preparing receptors in sensitive tissues to react.”
The ambiguity surrounding female athletes and anterior cruciate ligament injuries is not surprising, given that only 6 to 9% of sports scientific studies have focused on female athletes, according to a study published last year. However, the trend seems to be changing. “We are witnessing a real breakthrough in women’s sports,” says Nina Freitas. In 2024, Nike and the International Federation of Professional Footballers (FIFPRO) launched Project ACL, a three-year study to better understand anterior cruciate ligament injuries in female athletes. Additionally, the University of California, Berkeley announced a new initiative last year in support of women’s health, focusing on research related to female athletes, including anterior cruciate ligament injuries.
It is high time that anterior cruciate ligament injuries in young girls or women are taken more seriously. A torn anterior cruciate ligament can wreak havoc on the body and mental health of young girls and women and potentially end the careers of high-level athletes. According to orthopedic surgeon Sara Edwards at the Women’s Sports Center at the University of California, San Francisco, when the ACL is completely torn, surgery followed by nine to twelve months of intensive rehabilitation is the best course of action. Women are more prone to re-injury, and this “can become a lifelong problem,” Sara Edwards dreams. Liz Kitley remembers, “It’s such a long process… I missed my last NCAA tournament and ACC tournament. Then I had to go to the WNBA draft on crutches and couldn’t walk for a long time. It takes over your life, and having to deal with new problems almost two years later is really frustrating.”
While experts await more conclusive information, female athletes can take steps to protect their anterior cruciate ligaments. Programs like FIFA 11+, which include plyometric exercises, can reduce the risk of anterior cruciate ligament tears by up to 60%. “The biggest challenge is getting coaches to actually warm up or pushing teams to do it,” Nina Freitas reveals. Prevention programs can start from the age of six, says Sara Edwards, emphasizing the importance of educating coaches, parents, and athletes. Prevention is certainly not limited to young girls. The majority of patients followed by Sara Edwards are forty years old or older.
Finally, “there is no one answer” to explain why women are at higher risk, explains Joanne Parsons, an associate professor in the Department of Physical Therapy at the University of Manitoba in Canada. She, along with her colleagues Sheree Bekker and Stephanie Coen, suggest that social differences in treatment between female athletes and male athletes can contribute to increasing anterior cruciate ligament tear rates in young girls and women. Stephanie Coen emphasizes that it “is not about minimizing these biological factors but taking into account a range of other factors that may be important.”
For example, there are recognized inequalities in how young girls and women are exposed to games and sports, “a lifetime of gender-related exposures that have created unequal conditions in terms of risks,” says Stephanie Coen. Young girls and women are often introduced to sports later, play at unfavorable times or on lower-quality fields or courts than men, and do not use equipment tailored to their morphology, such as cleats. Many female athletes have more than one job, leading to muscle fatigue and making recovery after a tear more difficult. According to a FIFPRO report, more than a quarter of professional female footballers have a second job, earning an average salary of around 9200 euros per year globally.
Many female athletes of all ages are not encouraged to lift weights in the same way as their male counterparts, which is important for prevention, indicate Sara Edwards, Nina Freitas, and Emily Parker. “I am one of the first people to talk about a strength program to fourteen-year-old female athletes I see in the clinic… While male athletes of the same age are already experimenting with weightlifting with their friends or have already been introduced to the gym in a different way,” explains Nina Freitas. Fortunately, unlike anatomical differences, Joanne Parsons and Stephanie Coen point out that these gendered environmental differences are modifiable.
The goal of this increased knowledge is obviously not to hinder girls and women but to continue empowering them. “I don’t want it to seem like women should avoid the most physical sports,” clarifies Emily Parker. She adds, “to be honest, it’s more about acquiring more knowledge about the fundamental biological principles that affect women’s joint health to enable them to stay healthy when participating in sports.”
