Inside the ACL ‘epidemic’ plaguing women's soccer and the high-stakes search for cures
Claire Constant didn’t hear the dreaded pop, but did feel the jolt of pain. It shot through her body on May 16, two months before the tournament of her dreams. She’d been training, day after day, smiling and pushing toward her maiden World Cup — until she planted her foot in Portugal, saw her knee shift and nearly blacked out. “NO!” she screamed.
Because she knew the potential horror of non-contact knee injuries.
She knew that one tiny but critical ligament that runs through the middle of the knee, the ACL, had failed a stunning number of her peers.
She’d seen “many, many, many happen before my eyes” over her years in soccer, and so, lying on that field an ocean away from home, she instantly feared.
Teammates soon carried her to a training room. Over the coming hours and weeks, diagnostic confusion fueled hope. Constant, a 23-year-old starting defender for Haiti, wanted more than anything to experience the 2023 Women’s World Cup. She’d play through pain, through any injury that didn’t require surgery, to be there. “I think I’m OK,” she convinced herself.
But then came the final diagnosis. When she heard the three scariest letters in women’s soccer, “ACL,” she cried. And she joined a heartbroken club of elite players stricken by what some doctors now refer to as an “epidemic.”
Six of the world’s top 16 players tore an anterior cruciate ligament between June 2022 and April 2023. Five of them will miss the 2023 World Cup because of it. More than 150 top-flight players (and probably far more) have suffered the injury since last January. Many of the sport’s biggest names, from Marta to Alex Morgan, have endured it at some stage of their careers. Megan Rapinoe has overcome three ACL tears. Over a quarter of the 23 players who’ll represent the U.S. this summer have suffered at least one. And three other U.S. players — Catarina Macario, Christen Press and Tierna Davidson — will miss the World Cup in part because of this devastating injury, which typically requires 6-12 months of rehab.
As the epidemic went mainstream in 2022 and 2023 — as the club welcomed Spain’s Alexia Putellas, and France’s Delphine Cascarino and Marie-Antoinette Katoto, and Holland’s Vivianne Miedema, and England’s Leah Williamson and Beth Mead — people throughout the sport scrambled for answers. They learned rather quickly that, according to decades of research, women are two-to-eight times more likely to tear their ACL than men, but they wondered: Why?
They likely stumbled upon simple explanations — that various biological differences between sexes lead to the disparate injury rates — but those seemed unsatisfactory. They likely heard uninformed discussion of hormonal factors, but that, too, seemed to dodge the crux of the crisis.
“Yes, the medical science tells us one thing,” says Alex Culvin, a former player and current head of strategy and research at FIFPRO, the global soccer players’ union. “But it vastly overlooks the conditions that women footballers experience. And that is something that is missed [in] the dialogue around ACL injuries.”
And so, backed by a growing chorus of experts, the dialogue pivoted. Many of those experts question whether ACL rates have actually increased since the injury was first studied in the 1990s — definitive, population-wide data don’t exist — but, with the epidemic clearly out of control, some acknowledge the need for an altered approach. The early search for cures focused on biomechanics. The latest search spans “gendered environments” and a sport, women’s soccer, whose working conditions have lagged behind its rising physical demands.
“Women's football has had quite an evolution,” says Mario Bizzini, a Swiss researcher who worked with FIFA from 2002-2016 on injury prevention. “And maybe the parallel system — the support staff and everything — … is struggling to keep up the pace.”
Unraveling the ACL epidemic: A decadeslong search for answers
From her boutique office in Santa Monica, California, Holly Silvers-Granelli has watched this evolution, and watched with dismay as the list of stricken stars grew. She heard the public discourse crescendoing. And her mind flashed back to the start of her career in physical therapy, to the turn of the century, and specifically to a U.S. Under-19 women’s national team that suffered at least seven ACL tears, including three in a single month in 2002.
“It was crazy,” says Tracey Leone, the coach of that U-19 team. Her eyes would well with tears as it happened repeatedly. The injury, Leone says, “had always been really prevalent, but I felt like it was a little bit of an epidemic with our group.”
Silvers-Granelli also used that word, “epidemic” — in the early 2000s, and today. “This,” she says of the current crisis, “is such a fascinating rewind of history.”
Doctors first detected it in the late 1980s and '90s, as amateur women’s sports began to boom. Dozens of them traveled to Hunt Valley, Maryland, in June 1999 for a first-of-its-kind summit. At the Consensus Conference on Prevention of Noncontact ACL Injuries, they dissected reasons for the disparate rates in women and men. They discussed biological differences between males and females, “but the real question,” they later wrote, “is which differences, if any, contribute to an increased risk of ACL injury.” Over the years, dozens of theories have been posited, but the rough consensus honed in on two key factors:
Females, more so than males — in part because of their relatively wider hips — tend to land jumps or plant a foot with their knee angling inward. This is a “typical mechanism, predisposition for ACL rupture,” says Vincent Gouttebarge, FIFPRO’s chief medical officer.
Women tend to be more “quad-dominant” than men. That is, compared to men, they underuse back-of-leg muscles — hamstrings, glutes — and overuse front-of-leg muscles. There can be a strength imbalance, but “the other thing is muscle activation,” says Elizabeth Gardner, an orthopedic surgeon and team physician at Yale. “Just because you've got the muscle, doesn't mean that in that split second” — when a player reacts, and cuts, or decelerates, and calls upon the hamstring to absorb stress and protect the ACL — the muscle fibers will respond. “Women are, [on average, relative to men], particularly bad at activating all that posterior chain musculature,” Gardner says. This can expose the ACL.
Experts also point to minor anatomical factors — the actual diameter of the ACL, and the width of the “intercondylar notch” in which it sits, tend to be smaller in females — and to hormones. There is some evidence that, toward the middle of the menstrual cycle, if estrogen levels surge and ligaments get lax, female athletes experience greater ACL risk.
Opinions vary widely, however, on how significant hormones really are. Silvers-Granelli calls them “a very viable variable,” but a complicated one. Back in the late '90s and early 2000s, on the other hand, she theorized that biomechanics — how a person moves — were the most influential variable and, crucially, the most modifiable.
She and others studied the mechanisms of injury, and vowed: “Let's create the antidote, or the vaccination.”
They devised exercise regimens to build hamstring strength, to stabilize knees and train brains to activate muscles. In Cincinnati, Tim Hewett and his sports medicine colleagues built the first acclaimed program. Out in Southern California, Silvers-Granelli felt it was too time-consuming and onerous. She and renowned surgeon Bert Mandelbaum took similar concepts and retooled them into the PEP program, a soccer-oriented series of plyometrics, strengthening exercises and other dynamic warmups that fit seamlessly into the beginning of a training session.
They tested it on thousands of teenage girls, unsure of its effectiveness — Silvers-Granelli likens it to throwing darts at a board.
They found that it reduced ACL tears by 72-88%, and “Wow,” Silvers-Granelli thought, “that was pretty close to a bull's-eye.”
She and others, therefore, were irked when the epidemic exploded anew last year, and when players, journalists and fans bemoaned a lack of women-centered research. A 2021 examination of prominent sports medicine journals — entitled “‘Invisible Sportswomen’: The Sex Data Gap in Sport and Exercise Science Research” — found that only 6% of studies featured exclusively female participants. But here, “mercifully, in the ACL world, we started on the women's side,” Silvers-Granelli says. Her first two studies featured teenage girls and collegiate women’s soccer players. A third landmark study featured Norwegian women’s handball players. Each showed that prevention programs were effective.
And now, two decades later, they beg a vexing question: If the "antidote" is so efficacious, why is the epidemic still raging?
'Injury prevention is just not sexy enough'
Up in the hills of Switzerland, in the early 2000s, FIFA had been doing its own dart-throwing. Its Medical Assessment and Research Center (F-MARC) had piloted a catchy injury prevention program. But The 11, as it was dubbed, was unscientific and largely ineffective.
So its leaders contacted Silvers-Granelli. Together, they trekked up to Oslo, where they met a group of Norwegian researchers at Olympiatoppen. They molded Silvers-Granelli’s PEP program into an all-lower-extremity-injury prevention program, and rebranded it the FIFA 11+.
And just like the PEP, they found it remarkably effective — first in women, later in men.
So, in 2008 and 2009, they began presenting it at conferences, and meeting with national soccer federations, hopping from continent to continent, jetting around the globe to spread their gospel. Bizzini, the F-MARC’s chief evangelist, jokes that he traveled so much that “my wife got crazy.” He and colleagues tried to work with well-connected doctors, to embed the 11+ into coaching education courses. But here, in the implementation phase, they encountered their biggest obstacles.
They’d designed it, like the PEP, free of charge and equipment, as a 15-minute dynamic warmup, in hopes that every soccer team worldwide could do it twice a week and drastically reduce injury rates throughout the sport. But 15 years later, at amateur levels, uptake remains dispiritingly low. Somewhere in the chain of transmission from FIFA to doctors and federations, then to clubs, and to coaches, then to players, the prevention efforts often break down. At January’s United Soccer Coaches Convention in Philadelphia, for example, hundreds attended sessions on tactics or the business of youth soccer, but for a presentation on health and safety, led by U.S. Soccer chief medical officer George Chiampas, a cavernous room was virtually empty.
“Because injury prevention is just not sexy enough,” says Gouttebarge, the FIFPRO medical chief.
Many teams worldwide, Bizzini says, still only do “a bit of jogging, and a bit of stretching” before competing.
Across the American landscape, countless kids do similarly. Emily Fox, a U.S. women’s national team starter who tore her ACL twice in college, says that in her teenage years, she and teammates never did prevention exercises. “We would just hop on the field and just play,” she recalls.
Most professional clubs have adopted some sort of program. Some are variants of the 11+, beefed-up and modernized. The most advanced among them are individually tailored, player by player. Well-staffed clubs also take a more holistic approach. The NWSL’s Washington Spirit, for example, track menstrual cycles and sleep. They emphasize nutrition and all-around wellness. They screen players to identify deficiencies, and meet with them daily “to determine exactly what they need,” says Dawn Scott, the Spirit’s VP of performance.
But clubs like hers, she knows, are few and far between. Some others don’t even have access to trainers. “Yes, the women's game, it's been professionalized,” Scott says, “but is it professional? … Actually, in terms of your performance medical staff?”
The answer, in many cases, is no, and that’s one reason the discourse pivoted.
How gender, societal factors impact ACL injury risk
Joanne Parsons watched the epidemic spike from her home in Winnipeg, then watched her inbox fill. A physiotherapist by trade, Parsons had seen ACLs rupture. When she ventured back into academia for her Masters and Ph.D., she obsessed over ACL injury prevention. She read thousands of articles, and “over time,” she says, “I just got really tired of reading that it was biology to blame. It was because we were women, with hormones, that we have these injuries. … It just started striking me as very sexist.”
She began wondering whether existing research had overemphasized sex while ignoring gender. The former is a complex physiological blend of anatomy and hormones; the latter is roles and identities, a social construct that touches many aspects of human life, and Parsons wanted to explore how it affects ACL injury risk.
Take, for example, the refrain that women are worse at activating hamstring muscles. Is that purely biological? Or is it also because society has dissuaded them from building and training those muscles?
Resistance training, Parsons notes, is “the primary way you prevent injuries.” But the atmosphere around it, in hyper-masculine weight rooms, plagued by old-school female bodily ideals, often prevents girls and women from accessing it.
As the women's game is growing, and more games are being played, and more training sessions are being had, the resources need to grow as well.Naomi Girma
Parsons and two co-authors, in a 2021 paper, delved even deeper. They began in “pre-sport environments,” before puberty, to explain that even "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.” She cites studies that show that, by fourth grade, “girls and boys have different motor proficiencies. Girls can skip way better than boys. And boys can jump and throw better than girls. In Grade 4. In Grade 4, there's no biological or physiological reason why I shouldn't be able to throw as much as a boy. But it's those boxes we've put kids in.”
Those same boxes oppressed women’s sports for decades. They shaped a global soccer ecosystem that historically elevates boys and ignores girls. “Look at grassroots soccer in Europe,” Scott says. “Boys are in academies where they're fully staffed, [with] qualified staff, generally experienced, paid well. … Girls, at the same age, don't have that opportunity.” That opportunity promotes athletic development and refines biomechanics. “As you progress through the ages,” Scott continues, “and go through puberty, and you need to relearn mechanics and movement as the body grows, if you're not getting that support, you are kind of restricted in terms of your movement and your efficiency” — and thus, you are more susceptible to certain injuries.
Similar inequities flow up through the pyramid. A recent FIFPRO survey of 362 international women’s players found that, at their continental championships, “70% reported that the gym facilities were not of an appropriate level,” and “66% reported that the recovery facilities were not of an elite standard or provided at all.” Only 40% of those players, meanwhile, considered themselves full professionals. At most clubs, pay remains low and conditions lacking. Everything from equipment to medical expertise — all things that indirectly protect ACLs — pale in comparison to what elite men receive.
This is just a small taste of the factors that COULD be influencing risk. The factors may influence each other, and on any given day the factors have more or less influence, and they are likely different for every person. pic.twitter.com/IVt6JO6eQx
— Joanne Parsons (@J_ParsonsUofM) April 21, 2023
The business of women’s soccer, meanwhile, is blossoming away from its humble beginnings. Players are playing more often, in front of bigger crowds, after longer flights, at higher intensities. And the new prevailing theory behind the ACL epidemic’s latest spike is that support systems have failed to keep up.
“As the women's game is growing, and more games are being played, and more training sessions are being had,” says Naomi Girma, a U.S. defender who tore her ACL in college, “the resources need to grow as well.”
A growing sense of fear within the women's game
Back in Portugal, in the training room at SCU Torreense, a first-division club in a small town 45 minutes north of Lisbon, Claire Constant, the Haitian American defender, felt initial relief. Her pain had eased. The club’s trainer, Constant says, told her she’d torn her meniscus; the following day, another trainer said LCL, but neither said ACL. Constant hobbled around on crutches for three days, then resumed walking, with the World Cup still in sight.
But occasionally, her knee would buckle.
She asked for an MRI, standard practice to diagnose non-contact knee injuries; but the club, she says, refused. Two trainers had performed the Lachman test, a manual ACL test, and told her the ligament was intact. “I was told it was four weeks of recovery,” Constant says.
So she flew back home to Maryland. The following day, she went to a physical therapist — who did the same Lachman test, and detected an ACL tear. An MRI soon confirmed it. Constant was crushed. She broke the news to her coaches via WhatsApp. For a few days, she couldn’t stomach watching soccer of any kind.
One thing she never felt, though, was alone. Her close friend at the University of Virginia, Rebecca Jarrett, had recovered from the same exact injury. Several players interviewed for this story said they gleaned ironic comfort from the ACL club’s sheer size.
“I think that's what really blew me away in the process,” says Andi Sullivan, a U.S. women’s national team midfielder who tore her ACL in college. “Like, ‘Oh my gosh, so many people have done this.’” Rapinoe, the three-time ACL veteran, was one of the first players to reach out to Sullivan and lend support.
“I think it's been helpful that, honestly, so many people have gone through this experience,” says Davidson, the USWNT defender who tore her ACL last year — and whose fiancée, a former teammate at Stanford, had torn hers twice. “They've been able to give me advice, and quell my worries when I have them.”
Fox, the fellow USWNT defender, had a similar experience at the University of North Carolina.
But the prevalence has also begun to provoke fear. “I mean, the amount of ACLs that have happened this year and last year is scary,” Fox says. In London, Mead and Miedema, two sidelined teammates at Arsenal, would watch games together, “and every time someone has gone down injured and it has looked like their knee, you feel sick,” Mead told The Telegraph. When Williamson, their Arsenal teammate and England captain, crumbled to the grass during an April match against Manchester United and waved her arm in pain, Miedema, watching on TV, left the room in tears.
Mead, the 2022 Ballon d’Or runner-up, has become something of an unofficial spokeswoman for the ACL club, a frustrated advocate since tearing hers last November. Everybody — from Putellas, the Ballon d’Or winner, to doctors — knows that the injury is “multifactorial,” and that no single measure will erase it from the sport. But they also know that prevention programs can reduce the incidence, and proper professional support can help, and further research could identify other antidotes, all of which makes the recent rash of ACL tears even more excruciating.
“It’s way too common in the women’s game,” Mead said in March. “I think if that ever happened in the men’s game, a lot more would’ve been done sooner.”
