I wrote this article on behalf of all the young, female athletes I have been entrusted to return to the sports they love after non-contact ACL inuries….My goal with writing is to educate & empower girls, moms, dads and coaches to possible reasons why we have this problem on our hands and why FIFA’s funded research that is looking to highlight the menstrual cycle oversimplifies this problem. I would go as far as to say FIFA’s research is a potential distraction from reality.
Hypothesis.
FIFA’s working hypothesis on the link between menstrual cycles and ACL injuries is grounded in the idea that hormonal fluctuations—especially in estrogen, progesterone, and relaxin—may alter ligament laxity, neuromuscular control, and ultimately, injury risk.
“Swedish researcher Professor Martin Hägglund, challenges the hypothesis that the menstrual cycle significantly increases ACL injury risk in female footballers. He emphasizes that current scientific evidence does not conclusively support a causal link. Hägglund argues that structural, training, and resource-based disparities between men’s and women’s football are more likely contributors to the higher injury rate in women (February 2025 UEFA symposium). There’s no consistent evidence directly linking menstrual cycle phases to ACL injuries; structural, and training factors may be more significant.”
— Hägglund.
As a person who reads research daily, I have a million-dollar question for FIFA: Why are you focused on a factor that cannot be changed (ie: fluctuating hormones levels)? If a major cause is the fluctuations in hormones creating laxity what would be an ethical solution? Do we tell girls not to play soccer or basketball? Or sub them off when they ovulate? Are you aware of how many girls that do not even have a normal cycle and how hard it is to track hormones and ovulation definitively?
A History Lesson
Before we get into that though, I want to start with a history lesson. People who grew up in the 60’s, 70’s and 80’ accumulated far more hours of unstructured play during childhood compared to now giving those kids from the past a higher foundation of physical literacy and overall capacity. I’ll show you the data in a minute. Today, kids are specializing early, not as strong or fit as they once were and females are more apt to engage in sports that involve higher forces. I began training female athletes in 1998. In my time with UBC basketball as an example – from 1999 to 2006, our team average in push-ups was 35 reps (to fist) and the lowest back squat was 185 pounds, and the mean vertical jump was 17 inches. Currently, I do not have any female teenage athletes who can do even 10 push-ups well. Later on, I will explain how maximal strength training alters the strength of ligaments.
When looking at the data, adolescents in the 2020s perform worse across most fitness domains compared to the 1980s. The steepest declines are in aerobic endurance & relative strength & power.
Aerobic Endurance
~10–15% decline (~0.4–0.5%/yr)
Muscle Strength
~25–30 percentile loss in power tests
Power (Jump)
↓ 0.25–0.3 SD over ~20 years
As a strength & conditioning specialist with over 29 years of coaching female athletes in contact and collisions sports, plus a master’s degree in sport science and 18 years lecturing at the post secondary level…. I think I am at liberty to discuss this. Those on the surgical side and those who do the initial rehab do not have the perspective I do as a strength & conditioning coach. S&C Coaches know that long term athlete development and building bodies appropriately makes the most sense. We know that overloaded bodies where there is a poor foundation of strength does not bode well.
ACL Incidence Rates:
Female athletes are 2–8 times more likely to suffer ACL injuries compared to males in similar sports, with many studies converging around the upper range of that ratio. In youth sports, girls face particularly high rates:
Soccer (~0.166 per season) takes first place and (Childers et al)
Basketball (~0.103 per season) is in second place (Childers et al)
A broad adolescent-age review (over ~17 million athlete exposures =AE) found:
Females: 0.084 ACL injuries per 10,000 AEs vs. 0.060 for males.
Soccer had the highest rates: 0.166 per 10,000 AEs in girls (Bram et al)
Among elite adult females, non-contact incidents make up about 60–68% of all ACL injuries.
ACL Trends Over Time (30-Year Span)
Stable per-exposure rate: Evidence indicates incidence rates per exposure have remained relatively constant over decades (~1 knee injury per 1,000 AEs). (We will discuss why this perspective is biased in a little bit).
Rising total injuries: The number of female ACL injuries has increased sharply due to more females participating in high-risk sports (Source: The Guardian 2024)
ACL surgeries in U.K. adolescents have risen 29-fold over 20 years, mirroring higher participation and sport specialization.
OK, more and more girls are playing sports that have higher forces, but training disparities exist between the sexes!
Girls receive fewer strength/conditioning resources compared to boys—this is a social factor that can raise injury rates (Source: Danielson et al)
In elite women’s sports, like the WSL and NCAA, teams frequently underfund injury prevention (I prefer to say strength development), exacerbating the epidemic.
No, the FIFA 11 is not enough. Nimphius wrote an excellent review here recently.
In a new study in the British Journal of Sports Medicine, Richardson and her co-authors cast doubt upon explanations that rely solely on sex-linked biology. The researchers specifically honed in on “athlete-exposures,” a metric widely used in the field of sports science — and repeated without question by many journalists covering women’s higher rates of ACL injury. The popular measure embeds bias into the science, the researchers say, because it fails to account for different resources allotted to male and female athletes.
Bias is not our friend folks. An optimal study design has a cohort of female athletes following a long term strength development program over years and tracks incidence rate as compared to a similar cohort of girls who do not.
Now back to FIFA, let me educate you on the research they are funding:
A year-long, FIFA-funded study led by PhD student Blake Rivers at Kingston University (with partners like Chelsea & Fulham) commenced this month (June 2025). It will monitor oestrogen and progesterone levels alongside biomechanical testing—such as landing and direction‑change tasks—to explore whether hormonal phases correlate with ACL vulnerability.
Problems with this view
Biological factors (like hormones) intersect with social/environmental issues (training quality, support, resources thus focusing solely on biology oversimplifies a multifaceted problem.
Sure, they are also going to look at landing biomechanics, but how will they account for females who have never been taught how to land, how to jump, how to get strong, how to train for their sport etc etc.
They are studying the sport that has the highest number of ACL injuries - why not study rugby? same sex, same menstrual cycle - LESS ACL injuries.
It is all too common for female athletes to NOT get the support in strength & conditioning, when they likely need it the most.
So, what are the controllable solutions and what SHOULD FIFA be funding?
We know early implementation of strength & power training, and landing mechanics drills can cut ACL rates by 50–80% in young female athletes.
Coaches, clubs, and federations need to ensure female-specific programs, equitable access to medical/recovery support, and workload management.
But females have different Biomechanics!
“BULLSHIT THEY DO; Biomechanics are a modifiable risk factor. Here is precisely how Strength Training Improves & Changes Biomechanics:”
1. Enhances Joint Stability
Strong stabilizer muscles (e.g., glutes, core, rotator cuff) reduce unwanted joint movement.
Stability allows for more controlled, efficient, and aligned movement patterns.
Example: Glute strengthening reduces knee valgus (inward collapse), a major ACL risk factor.
2. Improves Motor Control and Movement Symmetry
Progressive resistance training improves neuromuscular coordination, allowing the body to move with better timing and rhythm.
Reduces compensatory patterns (e.g., excessive lumbar extension or hip hike during running).
3. Corrects Muscle Imbalances
Imbalances between agonists and antagonists (like quads vs. hamstrings) often lead to biomechanical inefficiencies and injury.
Targeted strength training helps restore force couples and proper kinetic chain mechanics.
4. Promotes Optimal Force Production
Well-trained muscles can produce more force with less effort and better directional control.
Leads to better ground reaction force management, jump/land mechanics, and change-of-direction ability.
5. Loads Tissues Functionally
Strength training loads tendons, ligaments, and fascia to increase tissue resilience and functional stiffness, important for spring-like movement (e.g., sprinting or deceleration).
LIGAMENTS need to be exposed to maximal strength efforts
What Happens During Maximal Voluntary Contractions (MVCs): (these are maximal strength-focused efforts). Too often females are underdosed in the weightroom. I know this, because I train 100’s of girls and a goblet squat with a 15 pound DB is not sufficient.
1. Increased Ligament Stiffness (Over Time)
Repetitive high-force loading (as in heavy strength training) may stimulate collagen synthesis in ligaments.
This could lead to a modest increase in stiffness or tensile strength over months.
Most of the evidence comes from animal models and long-term training studies in humans.
2. Improved Load Tolerance
Ligaments exposed to regular MVCs become better at handling high mechanical loads without microdamage.
This adaptation involves subtle changes in cross-linking of collagen fibers, contributing to strength—not elasticity.
3. No Change in Length or Laxity
MVCs do not shorten or "tighten" ligaments.
In individuals with ligamentous laxity, the passive joint restraint provided by the ligament remains unchanged, but functional stability improves due to stronger surrounding musculature.
4. Potential Increased Blood Flow & Metabolic Activity
Repeated maximal contractions may temporarily increase local circulation and cellular activity near ligament insertions, supporting long-term remodeling.
Ligaments are poorly vascularized, so these effects are subtle and slow.
Parents – this is my advice:
Find your daughter a qualified S&C. This is your best investment. Get her on a long term development plan that includes rest days and days allotted to strength & power development. Ensure the sport she is involved in and the coaching staff buy into the importance of strength training. The FIFA 11 is not strength training. It’s nothing more than a warm-up. Soccer, you need to up your game and stop turning these girls into endurance athletes who take contact. The menstrual cycle is here to stay.
If you have an athlete (female or male) coming back from an ACL injury and you need help with her or his return to play check out my course ACL Rehab Exercise Prescription from A-Z This in-depth course is designed to provide strength and conditioning coaches, athletic trainers, and rehab professionals with a step-by-step framework for designing ACL rehab programs that actually work. From early-stage recovery to full return-to-play, you’ll learn how to bridge the gap between rehab and performance. Click here to learn even more about my ACL Rehab Course.
Sources:
Bram JT, Magee LC, Mehta NN, Patel NM, Ganley TJ. Anterior Cruciate Ligament Injury Incidence in Adolescent Athletes: A Systematic Review and Meta-analysis. Am J Sports Med. 2021 Jun;49(7):1962-1972. doi: 10.1177/0363546520959619. Epub 2020 Oct 22. PMID: 33090889.
Childers J, Eng E, Lack B, Lin S, Knapik DM, Kaplan DJ, Jackson GR, Chahla J. Reported Anterior Cruciate Ligament Injury Incidence in Adolescent Athletes Is Greatest in Female Soccer Players and Athletes Participating in Club Sports: A Systematic Review and Meta-analysis. Arthroscopy. 2025 Mar;41(3):774-784.e2. doi: 10.1016/j.arthro.2024.03.050. Epub 2024 Apr 29. PMID: 38692337.
Danielsen AC, Gompers A, Bekker S, et a., Limitations of athlete-exposures as a construct for comparisons of injury rates by gender/sex: a narrative review., British Journal of Sports Medicine 2025;59:177-184.
