Holly McNamara knew what had happened even before she hit the ground.

In the 72nd minute of Melbourne City's A-League Women's match against Sydney FC last week, the City forward accelerated towards opposition midfielder Taylor Ray, trying to close her down.

As Ray cleverly nipped the ball away, McNamara's unexpected change of direction caused her left knee to cave inwards.

McNamara immediately yelped in pain, recoiling and grasping at her leg as she collapsed into a heap in the grass.

Her shrieks echoed around the AAMI Park stands. Everybody knew what they meant.

Ray, a veteran of two serious knee injuries herself, recognised the sound: of pain, of disappointment, but also fear — fear of what it could mean for a young player whose football career was only just starting to blossom.

"At first I didn't know what was going on when the ref stopped the game, but then I turned around and was like, 'Oh no, something's happened.'

"I watched the replay on the big screen and I knew straight away that it was an ACL injury."

McNamara now joins Ray in that most unwanted of clubs: sustaining multiple ACL tears before the age of 20.

Having suffered her first as a 15-year-old, McNamara burst back onto the domestic scene this season with Melbourne City.

Her form, dynamic style, and output – with four goals and three assists – earned her a call-up to the senior Matildas for February's Asian Cup. She is widely touted as one of the brightest young stars in the Australian game.

But the 20-year-old will have to put everything on hold once again and potentially plan a different future for herself.

Ray knows what it's like to be in those dark places, too.

"You're like, 'Why did this happen to me again? What did I do to deserve this? What could I have done differently?' All those 'what ifs' — that's what destroys you mentally.

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"Especially when it's your second ACL, because you've gone through that process before. So to think you have to go through every single stage again before you can return, that's terrifying. It's a lot of hard work and a lot of sacrifices once again.

"It's so overwhelming. You want to take that time to yourself to be upset. It's OK to be devastated. Take the time to have that heartbreak and then you can change that mindset later on."

McNamara now begins the slow, painful journey towards recovery and, hopefully, a return to the game.

She will be surrounded by football's various support systems as she does so: from players like Ray, with whom she became friends as they rehabilitated together after their first ACL injuries in the Future Matildas program, to the staff and resources offered by her club Melbourne City and Football Australia.

But there are many women athletes around Australia who are not so fortunate.

In fact, emerging research suggests these wider networks and environments play a critical role not just in the rehabilitation of women from ACL injuries, but most importantly, in the likelihood of the injuries occurring at all.

A history of ACL injuries in women's sport

ACL injuries have disproportionately affected women compared with their male counterparts since data began being recorded in the 1990s.

Early theories around why women were more likely than men to sustain ACL injuries overwhelmingly pointed to "sex"-based biological factors: anatomy, physiology, biomechanics, hormones.

Women, in other words, were simply "built" differently to men, and that inherent difference made them predisposed to certain types of injuries — in the case of ACLs, three to six times more likely to sustain them.

But as research has evolved and more gender-specific data has been collected, this essentialised biological framing of women's bodies has started to be questioned.

Indeed, longitudinal studies have found that while the rate of ACL injury has decreased for men and boys over the past two decades, they have remained unchanged in girls and women, suggesting there is more than strict biological factors at play when it comes to explaining their existence — and therefore developing programs to prevent them in future.

This is what a new review in the British Journal of Sports Medicine begins to investigate. The authors argue that ACL research in sports science has historically been too focused on "sex"-based biological factors (what they call "intrinsic" influences) at the expense of cultural and environmental ("extrinsic") factors. In reality, though, the two are deeply intertwined.

Instead, the authors suggest what's needed is a more holistic analysis of the experiences of women in sport and the environments in which they prepare, train, and play.

This analysis, the authors write, should take into account the way extrinsic factors such as access to facilities (fields, gyms), staff (qualified physiotherapists, strength and conditioning coaches), equipment (footwear, warm-up programs), as well as wider systems and structures such as healthcare and medical insurance, youth development pathways, contracts, and professional standards all contribute to the increased risk of ACL injuries in women athletes.

The four stages of ACL predisposition for women athletes

These contextual, extrinsic factors often begin in childhood, or what the study terms "pre-sport" environments, where the bodies of boys and girls are subtly moulded to conform to wider gender stereotypes.

From day one, "gendered parenting … for example, purchasing different toys or allowing greater independent mobility for boys … could manifest as altered movement patterns in sport later in life," the study says.

These pre-sport environments and the way girls are taught to use their bodies are then carried into adolescent "training environments", where wider social forces like peer pressure and body image begin to play a more powerful role.

For example, ACL research overwhelmingly suggests resistance training and increasing muscle mass is one of the primary methods for strengthening knees and preventing ACL injuries. However, cultural expectations and stereotypes around femininity and how women's bodies should look often affect girls and women's participation in these kinds of activities.

Ray has seen the toll these social pressures can take on her own teammates.

"So that mental side of things comes into play, eating comes into play, strength training comes into play. It's 'if I do this, I'm going to look a certain way, but then what if that affects my performance?'

"Your body is going to change not only because you're going through puberty, but because you're adding muscle mass, and I think some girls get scared of that because figure and image is so important these days."

Other gendered factors at this stage include the fact that most strength and conditioning coaches are male, while public spaces such as weight rooms in gyms are populated largely by men, contributing to deeper insecurities that women do not belong there.

As the authors remind us: "Before we assume that training for ACL injury prevention needs to be different for girls/women and boys/men, we need information as to the gendered environments that already exist. It is likely that training is already different, but in a way that disadvantages girls/women."

The third stage is the "competition environment" where athletes begin to compete in organised sport, which is divided into two clear gendered binaries from teenage years.

"By its very nature, sport places girls/women and boys/men in different playing situations," the authors write.

Research has found that the age bracket between 14 and 18 is when girls are most likely to sustain their first ACL injury. It is also the bracket when girls are most likely to drop out of competitive sport altogether.

While puberty may play a role in the higher rate of ACL injuries for teen girls, there are other powerful extrinsic factors at play including aforementioned social pressures around body image and participation in more 'acceptable' feminine activities, as well as increased responsibilities placed on young women to begin making longer-term life and career choices.

The lack of visible pathways towards professional sporting careers for women means they are less likely to undertake the kind of physical training and preparation at lower levels as their male counterparts with similar ambitions.

The final environment the study examines is the "treatment environment", or what happens during the rehabilitation phase after women sustain ACL injuries.

The authors suggest gender-based biases could play a role in the way women athletes are treated within the medical setting, including how regularly and quickly they're offered ACL reconstructions, their access to physiotherapy equipment and staff, and wider financial stresses such as juggling other jobs or family responsibilities that could affect a smooth rehab process and return to pre-injury fitness.

Ray has experienced that, too.

"I was still at school coming back from my ACLs, so I had to balance that with going through my HSC," she said.

"I'm very fortunate that I had such high-level professionals that wanted the best for me [at Sydney FC and Football Australia], but at the end of the day, I did a lot of individual work by myself.

"It's not like most full-time men players who can go into training every day and that's the only thing they're focusing on. Women footballers have other things they've got to consider.

As a result, according to the study, "boys and men return to sport more quickly than girls and women after ACL injury, which … could relate to the types of training environments that women and men experience and have access to during rehabilitation.

"Likewise, the wider gendered context of women's and men's lives (e.g. inequalities in familial and domestic labour) may create different opportunities and constraints for women and men to complete effective rehabilitation.

How is Australian football addressing ACL injuries in women?

For the past 10 years, Football Australia (FA) has been reviewing world's best practice and implementing programs specifically targeted at preventing these kinds of injuries.

For Kate Beerworth, FA's Female Athlete Health & Performance Consultant and current physiotherapist for the Australian Women's Cricket Team, one of the most important developments in the women's game has been observing and collecting more data around the injuries themselves and how, when, and where they happen.

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She said injury surveillance "is the underpinning of everything we do in terms of making change", but it takes time and money.

"There was a period where a number of Matildas and Young Matildas had ruptured their ACLs over a twelve-month period, and so from an organisational point of view, we had a platform to explore what we could do to reduce injury risk," Beerworth told ABC Sport.

"And so when we talk about injury prevention, it's a bit like the COVID vaccine: it's trying to apply it to everyone, not knowing who you're going to prevent from sustaining an injury, but with the intent to reduce the overall numbers.

"There's certainly things you can do at an individual level if someone's in a higher-risk category – that being if they've had a previous ACL injury or if they've got a family history – but the systemic approach is to apply that 'vaccine', if you like, or that program to as many athletes as you can.

"There are multiple reasons why someone does their ACL, so our job is to try and control the controllables, then put practices in place that can change some of those modifiable factors – strength is certainly one, [and] the age of when you introduce that has been shown to be really important."

As more women's sports move towards full-time professionalism, experts will finally be "able to compare apples with apples", instead of just comparing the experiences of women to that of men as they've often done in the past.

Football's advantage in this space is that its global nature allows for knowledge-sharing across various clubs, leagues, and federations around the world. And more available data means more opportunities to collaborate and accelerate research.

One of the programs FA currently have in place is called "Perform+". It's an updated version of FIFA's "11+" primary prevention framework that was first developed in 2006, which has been shown to reduce ACL injuries in football between 40 and 50 per cent when completed by athletes at least twice a week.

But conclusive data has been difficult to compile in Australia given a lack of knowledge translation, poor coach compliance with the program, and a lack of education across various levels of the game.

FA have tried to address that knowledge gap by ensuring their own "Perform+" framework is included in coach education packs and listed on the governing body's website for easy, free access.

FA's program only takes a total of 20 minutes and includes exercises involving ball/player contact (landing technique), changes of direction in a controlled environment, and strength work, all of which can be spread across warm-ups, in between drills, or during cool-down sessions. It's now used right across Australia's senior and junior national teams as well as adapted throughout A-Leagues clubs.

Dr Matt Whalan, FA's physiotherapist and Player Availability & Perform+ Coordinator, helped create the program. One of his modifications to FIFA's original design was ensuring that injury prevention was viewed as more than just a list of exercises, but also included contextual "extrinsic" information specific to women footballers and their environments.

"Training age, accessibility to resources, exposure to strength and conditioning compared to male players – even just access to the facilities are all a big part of it," Whalan told ABC Sport.

"All those things come into consideration with women being two to three times at greater risk.

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"Most [elite] clubs will have some sort of injury prevention program that they do. In that setting, because most of them would have strength and conditioning coaches and physios, in some ways, if you've got to that level [as a woman athlete], you've kind of survived. How many have we lost down the pyramid that never get to that point?

"There's so many other factors we need to address as a community to actually achieve equity in this scenario."

Another advantage football has over other women's leagues such as AFLW, which is experiencing a spate of ACL injuries this season, is the opportunity for players to start learning crucial movements in controlled settings from a younger age.

"I think the training age concept is a really big one here," Whalan said.

"When you look at AFLW, especially those first couple of seasons, there seemed to be a fair few players who went from basketball or netball over into AFLW, which have similar movement patterns, but they are quite different at the same time where you're going from stop to start and changes of direction.

"Then you look at the potential success within the Football Australia set-up where, in the Future Matildas program, they're training hard three or four times a week, so from a younger age there's strength and conditioning, not waiting until they get to the senior level.

"Exposure to the training environment, strength and conditioning components, and the movements of the sport are so important in that younger age group, which is why it's so devastating when a 14-year-old does their ACL, because they're out for a year; that's a year of loss of skill acquisition, movement control, and then they come back in. That's the part that's hard to catch up on."

As ever, what's needed is more data to better understand how these multiple biological and environmental factors contribute to women's susceptibility to ACL injuries.

But as Beerworth said, the first step that all sports can take in preventing knee injuries is to "control the controllables".

This means providing women athletes with professional training environments, accessible equipment and facilities, qualified staff, and development opportunities from a younger age, in addition to securing long-term contracts that give players financial security throughout the rehabilitation process, as well as continuing to lift minimum standards on and off the field.

As emerging research is beginning to highlight, all of these cultural and environmental factors coalesce to make women more susceptible to career-ending injuries. The sooner that sport provides equitable environments for these players – from grassroots through to the elite level – the less likely bright stars like McNamara are lost before they've really had a chance to shine.