Bowdoin Science Journal

Women's health

Timing Matters: How the menstrual cycle influences ACL injury in Female athletes

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The knee, one of the major joints of the body, powers athletes in their endeavors; it is made up of three bones (the femur, tibia, and fibula), which are scaffolded by a milieu of muscles and ligaments. Injuries most often occur on this scaffolding. A particularly devastating injury is the tear or partial tear of the anterior cruciate ligament (ACL). This ligament is tasked with holding the femur and the tibia together and preventing excessive rotation and forward slipping. ACL tears happen when an individual pivots or puts too much sideways pressure on the knee(Knee Joint).

Unfortunately, female athletes are disproportionately affected by this injury in comparison to their male counterparts. In part, it is due to anatomical differences in the alignment of the leg bones. For example, female pelvises tend to be wider, which increases the Q-angle (the angle between the quadriceps and the patellar tendon). This predisposes the knee to collapse inward and give way to ACL tears. However, this is not the only factor on a small scale; hormones are also to blame. In turn, it seems as though the menstrual cycle has an impact on the ACL’s propensity for injury in women(Why Do Young Female Athletes Face Higher Risk for ACL Injuries?).

 

The menstrual cycle is a 28-day hormonal cycle that governs female reproduction. It is made up of 3-4 phases: menstrual, follicular, ovulation, and luteal. The follicular phase and the menstrual cycle are often grouped. Throughout the cycle, different hormones ebb and flow. The main ones are FSH (follicle-stimulating hormone), LH (luteinizing hormone), estrogen, elastin, and progesterone. These are all hormones that are responsible for moving the menstrual cycle along, ranging from the release of the egg from the ovary to the thickening of the endometrium. For example, estrogen is responsible for triggering the thickening of the uterine lining and the release of the egg from the ovary (Wojtys et al., 1998). 

(Menstrual Cycle | Description, Phases, Hormonal Control, Ovulation, & Menstruation | Britannica)

Wojtys et al. investigated whether the menstrual cycle phase actually had anything to do with ACL tear risk, especially since most earlier studies focused only on structural differences between male and female knees. The athletes they studied were mostly in their mid-20s and played sports like soccer, basketball, volleyball, track, gymnastics, and skiing—all activities where non-contact ACL tears are common. Each woman filled out a questionnaire that asked about her menstrual cycle (things like typical cycle length, when her last period started, whether she used birth control, and whether her cycles were regular) as well as the exact situation in which the injury happened. Only women with consistent, regular cycles were kept in the sample, which left them with 29 usable responses (1998).   

 

What they found from all this was a clear correlation between menstrual cycle timing and ACL injury, with women most likely to tear their ACL during the ovulation phase, which is when relaxin and estrogen peak. As the name suggests, relaxin is responsible for the relaxation of ligaments and tendons. Outside of the uterus, estrogen is also responsible for the reduction of ACL tensile strength and an increase in laxity. Similarly, relaxin causes a restructuring of collagen, which is theorized to play a role in the susceptibility to ACL injury. (Relaxin.; Wojtys et al., 1998)

 

An interesting note is that women on oral contraceptives seemed to have lower injury rates. Birth control’s mechanism is stopping ovulation (the phase in which most injuries were observed). Hormonal birth control keeps estrogen levels much more stable by preventing the mid-cycle estrogen surge, so instead of a sharp spike during ovulation, estrogen stays at a steadier and lower baseline. Since that spike is linked to increased ligament laxity, this hormonal stabilization may help reduce the ACL’s vulnerability to injury(Wojtys et al., 1998).

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This study provides support for the theory that part of the increased likelihood of females for ACL injury, in addition to the mechanical theory, brings forth a hormonal argument. It is worth noting the limitations of the study, however. These are also discussed in the literature itself. The main issue is the accuracy of the self-report. The women were asked at what point they were in their menstrual cycle, as there was no official tracking, there may be inconsistencies here. Moreover, the range in age and level of activity is quite large, especially in such a small sample size (29 individuals). 

 

This type of study can be part of the picture in injury prevention for athletes. ACL tears in particular, are quite devastating injuries. These season enders take 9-12 months to fully heal, in turn barring return to a competitive sport for an extended period of time (Writers, 2021). The consideration of hormonal fluctuations affecting ACL tears can influence training strategies and open the door to understanding oral contraceptives as a preventative measure. 

 

Further directions expanding upon this study could be looking at the menstrual cycle in a more controlled manner, in addition to looking at other connective tissue injuries. Ultimately, the mechanism of soft tissue can be better understood with a deeper view into alternative factors such as hormonal shifts.

 

References

BCOS. (2023, May 23). What is an ACL Injury? | Symptoms, Causes, & Treatments | BCOS. Burlington County Orthopaedic Specialists P.A. https://burlingtoncountyortho.com/blog/what-is-an-acl-injury/ 

Knee Joint: Function & Anatomy. (n.d.). Cleveland Clinic. Retrieved December 24, 2025, from https://my.clevelandclinic.org/health/body/24777-knee-joint 

Menstrual cycle | Description, Phases, Hormonal Control, Ovulation, & Menstruation | Britannica. (n.d.). Retrieved December 24, 2025, from https://www.britannica.com/science/menstrual-cycle 

Relaxin: Hormone, Production In Pregnancy & Function. (n.d.). Cleveland Clinic. Retrieved December 24, 2025, from https://my.clevelandclinic.org/health/body/24305-relaxin 

Why Do Young Female Athletes Face Higher Risk for ACL Injuries? (n.d.). Retrieved December 24, 2025, from https://www.cedars-sinai.org/newsroom/why-do-young-female-athletes-face-higher-risk-for-acl-injuries/ 

Wojtys, E. M., Huston, L. J., Lindenfeld, T. N., Hewett, T. E., & Greenfield, M. L. (1998). Association between the menstrual cycle and anterior cruciate ligament injuries in female athletes. The American Journal of Sports Medicine, 26(5), 614–619. https://doi.org/10.1177/03635465980260050301 

Writers, Uch. (2021, October 14). How long is recovery time from an ACL tear? UCHealth Today. https://www.uchealth.org/today/acl-tears-how-long-does-it-take-to-recover-and-return-to-sports/

The Contraceptive Brain Drain: How Birth Control Alters Women’s Brains

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There are millions of women taking steroids every day. But how is this possible? Are they just getting really buff? It feels like we always hear stories about how performance-enhancing drugs, namely steroids, are giving world-class athletes the boost they need to beat out their competition. But women across the globe are taking steroids every day as well, in the form of hormonal birth control. Despite their widespread use, side effects of hormonal contraceptives are largely unstudied, or have been until recently. In the last ten years, several studies have come out about the effect of taking a daily dose of steroids on women’s brains and mental health, which until now has been a severely neglected area where lack of knowledge affects millions of people worldwide. 

People take hormonal birth control, or hormonal contraceptives, for a myriad of reasons, from the obvious (preventing pregnancy) to the not-so-obvious (lessening iron deficiency) and everything in between. This type of medication simply refers to methods of pregnancy prevention that act on the endocrine system. The endocrine system controls growth, development, metabolism, and reproduction via signaling molecules called hormones. Two hormones in particular, estrogen and progesterone, control the menstrual cycle and are therefore the major components of hormonal birth control. Types of hormonal contraceptives come in many forms including the pill, the patch, the implant, injections, and hormonal intrauterine devices or IUDs, but despite the wide variety in the forms this medication takes, all of them contain one or both of these two hormones. As steroids, both estrogen and progesterone affect other body systems besides the reproductive system.

To study the impacts of taking a daily dose of steroids on other areas of the body, specifically the brain, Dr. Belinda Pletzer and her colleagues conducted a study in 2010. The brain is particularly susceptible to change due to an influx of synthetic hormones because it contains a very high quantity of hormone receptors. The brain needs to act as a “sponge” for these molecules since it plays an important role in creating the appropriate responses in the rest of the body. Pletzer’s study investigated how the sponginess of the brain would affect changes in its structure by comparing images of the brains of adult men, adult women during different stages of their menstrual cycle, and adult women taking hormonal contraceptives. To perform this comparison they used a technique called voxel-based morphology on MRIs of study participants (Pletzer et al., 2010). Voxel-based morphology measures differences in the concentration of tissue and the size and shape of different areas of the brain.

Overall, they found that women taking hormonal birth control had smaller areas of gray matter, or areas of the brain that have a high concentration of the cell bodies of nerve cells, when compared to “naturally cycling women” in both their follicular and luteal menstrual phases (Figure 1). Pletzer’s study also found interesting gendered differences in gray matter volume. While men had greater gray matter overall, the volume of gray matter in the prefrontal cortex, the pre-and postcentral gyri, and the supramarginal gyrus of both naturally cycling women and women taking hormonal contraceptives was higher than the volume of gray matter in these areas in men (Figure 2). These areas are involved in decision-making and problem-solving, controlling motor function, and emotional responses. However, the higher amount of gray matter in women in these areas was overshadowed by the larger volume of gray matter in men in the hippocampus, hypothalamus, parahippocampal and fusiform gyri, putamen, pallidum, amygdala, and temporal regions of the brain during the early follicular phase (A), mid-luteal phase (B), and in women taking hormonal birth control (C) (Figure 2). Many of these areas of reduced gray matter are ones of high importance for neurophysical ability and mental health.

Additionally, a study done by Rush University Medical Center showed an association between higher levels of gray matter and better cognitive function (“Everyday Activities Associated with More Gray Matter in Brains of Older Adults”). These findings suggest that taking birth control, and the associated decrease in gray matter, could be directly causing some of the symptoms women on hormonal contraceptives experience, such as brain fog, mood changes, and even anxiety and depression. For example, a smaller hypothalamus, one of the areas of decreased gray matter, is associated with heightened irritability and depression symptoms (“Study Finds Key Brain Region Smaller in Birth Control Pill Users”). Pletzer’s research and the work of others after her on the impact of birth control on structures of the brain represent important first steps in proving a causative relationship between birth control, symptoms associated with it, and structural changes in the brain.

Although this research has made some crucial preliminary steps into researching how taking a daily dose of steroids affects the brains of women taking hormonal contraceptives, the highly complex nature of the brain and its relationship with the regulation of the rest of the body means that further research is necessary. The sheer number of people that this issue affects means that it is essential to continue researching the impacts of this widely used drug. More importantly, knowing the potentially serious negative side effects enables millions of people to make more informed decisions concerning their health and their bodies.

 

Works Cited

Rush University Medical Center. (2018, February 14). Everyday activities associated with more gray matter in brains of older adults: Study measured amount of lifestyle physical activity such as house work, dog walking and gardening. ScienceDaily. Retrieved March 11, 2023 from www.sciencedaily.com/releases/2018/02/180214093828.htm.

Lewis, C. A., Kimmig, A. C. S., Zsido, R. G., Jank, A., Derntl, B., & Sacher, J. (2019). Effects of hormonal contraceptives on mood: a focus on emotion recognition and reactivity, reward processing, and stress response. Current psychiatry reports, vol. 21, no.11, 2019, p 115. PubMed Central, https://doi.org/10.1007/s11920-019-1095-z.

Meyer, Craig H., Kinsley, Elizabeth A. “Women’s Brains on Steroids.” Scientific American, https://www.scientificamerican.com/article/womens-brains-on-steroids/. Accessed 7 Mar. 2023.

Nemoto, Kiyotaka. “[Understanding Voxel-Based Morphometry].” Brain and Nerve = Shinkei Kenkyu No Shinpo, vol. 69, no. 5, May 2017, pp. 505–11. PubMed, https://doi.org/10.11477/mf.1416200776.

Pletzer, Belinda, et al. “Menstrual Cycle and Hormonal Contraceptive Use Modulate Human Brain Structure.” Brain Research, vol. 1348, Aug. 2010, pp. 55–62. ScienceDirect, https://doi.org/10.1016/j.brainres.2010.06.019.

Sharma, Rupali, et al. “Use of the Birth Control Pill Affects Stress Reactivity and Brain Structure and Function.” Hormones and Behavior, vol. 124, Aug. 2020, p. 104783. ScienceDirect, https://doi.org/10.1016/j.yhbeh.2020.104783.

“Study Finds Key Brain Region Smaller in Birth Control Pill Users.” ScienceDaily, https://www.sciencedaily.com/releases/2019/12/191204090819.htm. Accessed 7 Mar. 2023.