November 20, 2024 | 10 minute read

How Project ACL seeks to tackle the ACL injury "epidemic" in women's football

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Sofia Sportelli

Co-Authors

Isaac Thurgood

Get in touch

Sofia Sportelli

Co-Authors

Isaac Thurgood

Project ACL is a collaboration between FIFPRO (The Federation of Professional Footballers), the Professional Footballers Association, Nike and Leeds Beckett University to accelerate research into Anterior Cruciate Ligament ("ACL") injuries in women's football.

The ACL runs diagonally in the centre of the knee and is essential for stabilising the joint. Sudden twisting movements or high-force impact to the knee can stretch, tear, or completely rupture an ACL. Depending on the severity of the injury, treatment will typically involve a reconstruction surgery and months of physiotherapy. While prevalent in nearly all sports, notably those with rapid changes of direction and pivoting, they are particularly pervasive in football. In the UK, football injuries are responsible for nearly half of all ACL reconstruction surgeries[1]. For an athlete, this devastating injury means being sidelined for a recovery period of around 9-12 months, although there is no guarantee of a full return to sport.

While ACL injuries impact both male and female footballers, they are between 3-6 times more likely to occur in women[2]. Labelled an “epidemic” in women's football, over 25 players missed the 2023 FIFA Women's World Cup due to ACL tears[3]. Despite this, there is little understanding as to why this is the case[4]. There are several factors which have been identified as contributors for women, such as strength and conditioning deficits, equipment, fixture congestion and physiological and hormonal differences, which will be explored. However, the impacts of these elements remain inconclusive. Emma Hayes, head coach of the United States ("US") women's national team, commented that ACL injuries in women "should not casually just be blamed on ‘the players playing too many games’ or ‘the pitch is too dry’. That’s too easy. That’s lazy”[5]. This complex gendered issue remains a mystery.

Project ACL

Project ACL was created after urgent calls for action to address these injury rates in women. As Dr Alex Culvin, FIFPRO's Head of Strategy and Research for Women's Football, has noted, players themselves pushed for more investigation and "Project ACL is a response to both their needs and those of the industry more broadly"[6].

It is scheduled to run for three years, and in this time, three aspects will be focused on[7]:

Firstly, current scientific literature relating to injury prevention, football and ligament damage will be reviewed to consolidate existing knowledge and identify research gaps.
Secondly, a needs-based assessment of each the 12 clubs in The Women's Super League ("WSL"), the top tier of women's football in England, will take place.
Thirdly, Project ACL will use the FIFPRO Player Workload Monitoring Tool to track, in real time, the workload and travel schedules of WSL players. Crucially, this data will be utilised to identify their “critical zone” appearances. This is where two matches are played with less than five rest days separating them, and more than 45 minutes are played in both[8].

Dr Culvin also observed how interest in ACL injuries has expanded as the professionalisation of women's football has increased in recent years[9]. Certainly, the rapid growth in women's football, dubbed the 'Lioness effect' after England won the European Women's Championship in 2022, has enhanced demands on players.

Combining findings from these three action steps, Project ACL partners will be able to streamline their advice on optimum injury prevention and recovery methods to both clubs and players. Project ACL is forecast for expansion. At present, 7 of the 12 WSL clubs have agreed to be assessed on their facilities, training, scheduling and player wellbeing systems. It is expected that more clubs will participate in the 2024-25 season, and it is hoped that the scheme will later be expanded to professional leagues worldwide.

Risk Factors Identified in Research

1. The Q-Angle

The Q-angle is the angle that forms between a hypothetical line drawn from the hip joint to the knee, and then the knee joint to the ankle joint. The Q-angle theory is that the average woman has wider hips than the average man, and, therefore, a larger Q-angle[10]. This means that there is a greater relative force being transferred through the knee with each stride. It follows that this is responsible for the increased injury risk in the knee.

Most women’s ACL injuries are non-contact, ‘planting’ related injuries[11]. Some of this is related to equipment and the fact that ‘good technique’ has been modelled on men, but there is a higher incidence rate in women whose surrounding muscles have grown at a different rate to the bone, placing the ligament under increased strain[12]. It is a recent advent that, when it comes to sport in particular, women are no longer (exclusively) considered ‘small men’[13]. Even then, much of the research considered women‘s sport in relative to men’s sport[14]. This analytical framework led to the Q-angle emerging as the dominant explanation as to why women are 3-6 times more likely to suffer an ACL injury[15]. Whilst not dismissed, more recent scholarship has problematised this over-reliance on the Q-angle as an explanation for why there is a disproportionately high incidence rate of ACL injuries in women’s sports.

2. Strength and Conditioning

Despite the growth of women's football, the level of professionalisation has not fully kept up with new demands of the sport. This is echoed by Karen Carney, former professional footballer in the WSL, who highlighted the lack of resources, medical support and strength sessions offered to female players[16]. Aston Villa and England midfielder Lucy Staniforth stated, "most women's players have had staff that are maybe fresh out of university or coming from a men's football background that don't necessarily have the knowledge and appreciation of what a women’s athlete needs"[17].

Studies have shown that women typically have less muscle mass surrounding the knee, due to both biological factors and less frequent strength and conditioning ("S&C") programming. In a 2022 comparison of strength training methods between men's and women's football, at first team or academy level worldwide, it was found that there are fewer weekly in-season S&C sessions which "may have negative implications for physical development and injury risk"[18]. Any force absorption muscles cannot provide gets passed onto ligaments. As sufficient muscle mass can prevent joint instability, without this, ligaments may become overstretched and eventually tear[19].

3. Equipment

Sports equipment is rarely specific to women[20]. There is extensive dialogue on how smaller sizes of men’s boots are inappropriate for women. Fortunately, this has been accepted by equipment manufacturers[21]. Research has shown that the majority of women’s ACL injuries are non-contact, occurring at the point of plant/pivot in the knee joint[22]. Analysis of men’s plant-foot when striking a ball has shown a preference for a mid-foot to heel strike-zone (where the plant foot contacts the ground)[23]. Studies have indicated a slight difference in women, with a preference for a more mid-ball of the foot plant prior to kicking a ball. Therefore, it is possible that, when the stud placement on boots does not accommodate for gendered differences, then women wearing men-specific boots are at greater risk of plant/pivot-related injuries if the studs lock into the ground at an angle that is less than optimal for women’s anatomical biases.

4. Scheduling

Over the past ten years growth in the women’s game has meant more demands from sponsors and expanded international tournaments[24]. The theory follows that overtraining and saturated schedules create conditions that heighten the risk of ACL injuries. Such explanations have been problematised as “lazy”[25]. Growth in the women’s schedule broadly mirrors that of the men’s game; however, the men’s game has not seen the same incremental changes to ACL injury rates. This indicates that women’s scheduling cannot serve as a full explanation for the outsize ACL injury rates in women’s football.

Often, excessive fatigue means that sportspersons find it harder to ensure perfect technique. It stands to reason that planting and pivot injuries relate to “poor” technique. There are two issues with such a conclusion. The first is more obvious – telling professional sportspersons to avoid fatigue when training is impractical. The second is that granular data of professional sportswomen’s ACL injuries reveals that over 60% of injuries occur in the first half of games i.e. when there are lower levels of fatigue[26]. Players who are less fatigued are less likely to have lost focus on their technique, and therefore, less likely to be injured. At face-value, women’s football-related ACL injuries buck this trend. Perhaps this is explained by the fact that “good technique” remains modelled on men’s players and is less appropriate for women.

5. Hormones

Research has also focused its attention on the links between hormonal factors and ACL injuries. There is evidence that hormones such as oestrogen and relaxin, the latter of which is often mentioned in the context of pregnancy, cause greater laxity in ligaments, tendons and muscles throughout the body[27]. Greater laxity means ligaments are looser and more susceptible to strain, in turn creating a higher likelihood of tears and ruptures. In addition, as hormones fluctuate throughout the menstrual cycle, ongoing studies are attempting to identify time periods where women are most vulnerable to ACL injuries where specific levels peak[28]. However, the data in this area remains inconsistent. While it is established that ACL laxity varies across the menstrual cycle, the role oestrogen and relaxin play is not well understood[29]. Existing evidence is mainly gathered from predicted hormone levels, and exact measurements are not typically taken as this would be done with continuous sampling of blood from athletes pre- and post-ACL injury[30].

Nonetheless, as a testament to the importance of hormonal fluctuations, several women's teams in professional clubs, such as Chelsea, have introduced specialist apps to track their players' menstrual cycles[31]. Furthermore, in early 2024 UEFA allocated €20,000 to research the effects of the menstrual cycle on athletes' performance and wellbeing, and an equivalent sum has been allocated for the 2024/25 season[32]. This is with a view to reducing players' risk of injury, notably ACL tears and other soft tissue damage, by tailoring their training schedules and implementing rest periods where necessary.

Conclusion

Lionesses captain Leah Williamson put it best, “the way you’re taking women’s football right now...you won’t have players to watch”[33]. What is clear is that something had to change, and although the reasons for gendered differences in ACL injury rates are not yet understood fully, something is changing.

Project ACL is testament to that shift in attitude. More women playing football means more attention on the sport. Sports science is beholden to research funding, and last year, medical insurance costs associated with ACL injuries ballooned to $17.7 billion in the US alone. Correspondingly, research funding has doubled[34]. This is a notable trend that insurance companies, particularly health insurance companies, will need to be conscious of, and perhaps be more proactive in continuing to fund research, following the model of prevention being more cost-effective than cure.

Similarly, with more commercial focus on women's sports, and more research funding, this will inform better, more women-specific equipment and resources. This presents a risk for current retailers of non-gender specific equipment, as their current female customers may pivot to women-specific equipment born out of increased funding of this research and development.

The explanation is most likely a confluence of factors, including hormonal fluctuations; poor strength and conditioning; and male-specific technique and equipment. At this stage, the explanation is a series of theories underpinned by varying degrees of as-of-yet inconclusive empirical data. However, with more focus and attention, there is cause for optimism that there will be concrete explanation, and injury mitigation tactics will be put in place for players at every level of the game.

[1] Future of Football: Why ACL injuries have been on rise in women's game - and the technology and solutions to fix it | Football News | Sky Sports

[2] https://bjsm.bmj.com/content/55/17/984

[3] Future of Football: Why ACL injuries have been on rise in women's game - and the technology and solutions to fix it | Football News | Sky Sports

[4] Players share invaluable insights and experiences at Project ACL launch event - FIFPRO World Players' Union

[5] Your pelvic floor is the epicentre of everything for a female athlete (telegraph.co.uk)

[6] FIFPRO, PFA England, Nike & Leeds Beckett University launch project to reduce ACL injuries in women’s football - FIFPRO World Players' Union

[7] Ibid.

[8] https://fifpro.org/media/stwbbrax/match-workload-travel-and-injuries-in-elite-women-s-football.pdf

[9] Dr Alex Culvin: Are we asking the right questions on ACL injuries? - FIFPRO World Players' Union

[10] Why Women Have More ACL Injuries Than Men | Northwestern Medicine

[11] Bailey, M., British Orthopaedic Association, How to Tackle ACL Injuries.

[12] Ibid.