Paper wasps have a knack for recognizing faces, and a new study adds to our understanding of what that means in a wasp’s brain.

Most wasps of a given species look the same, but some species of paper wasp (Polistes sp.) display varied colors and markings. Recognizing these patterns is at the core of the wasps’ social interactions.

One species, Polistes fuscatus, is especially good at detecting differences in faces — even better than they are at detecting other patterns. To zero on the roots of this ability, biologist Ali Berens of Georgia Tech and her colleagues set up recognition exercises of faces and basic patterns for P. fuscatus wasps and P. metricus wasps — a species that doesn’t naturally recognize faces but can be trained to do so in the lab. After the training, scientists extracted DNA from the wasps’ brains and looked at which bits of DNA or genes were active.

The researchers found 237 genes that were at play only in P. fuscatus during facial recognition tests. A few of the genes have been linked to honeybee visual learning, and some correspond to brain signaling with the neurotransmitters serotonin and tachykinin. In the brain, picking up on faces goes beyond basic pattern learning, the researchers conclude June 14 in the Journal of Experimental Biology.

It’s possible that some of the same genes also play a broader role in how organisms such as humans and sheep tell one face from another.

Ancient rock artists were drawn to echo chambers. Members of early farming communities in Europe painted images in rock-shelters where sounds bounced off walls and into the surrounding countryside, researchers say.

Rock-shelters lacking such sound effects were passed up, at least in the central Mediterranean, report archaeologist Margarita Díaz-Andreu of the University of Barcelona and colleagues in the July Journal of Archaeological Science. In landscapes with many potential rock art sites, “the few shelters chosen to be painted were those that have special acoustic properties,” Díaz-Andreu says.
Some hunter-gatherer and farming groups studied over the past couple centuries believed in spirits that dwell in rock and reveal their presence via echoes. But acoustic evidence of special echoing properties at rock art sites is rare.

Díaz-Andreu’s team studied two rock art sites in 2015 and 2016. Baume Brune is a kilometer-long cliff in southeastern France. Of 43 naturally formed cavities in the cliff, only eight contain paintings, which include treelike figures and horned animals. Rock art in the Valle d’Ividoro, on Italy’s east coast, appears in an 800-meter-long section of a gorge. Only three of its 11 natural shelters contain painted images. Researchers generally date these French and Italian paintings to between roughly 6,500 and 5,000 years ago, several thousand years after the Stone Age had ended, Díaz-Andreu says.

To investigate the acoustics of the decorated and unadorned shelters, the researchers developed a new technique for determining the direction, intensity and timing of sound waves arriving at a particular point from every direction. A special microphone connected to a digital recorder measured the acoustic properties of any echoes set off by balloons popped just outside each rock-shelter. This setup was moved to various spots outside the caves to record the acoustic reach of reflected popping sounds. Echo measurements in France were taken at distances ranging from 22 to 36 meters from cliff shelters. Due to rougher terrain in Italy, measurements there were taken at distances ranging from 77 to 300 meters.
Then, the acoustic data were transformed into 3-D, slow-motion depictions of echoes, represented by moving circles, indicating where sound reflections originated. At both sites, shelters with rock paintings displayed better echoing properties than undecorated shelters, Díaz-Andreu says. And in each location, the shelter that best reflected echoes had the highest number of paintings.
“This novel technique shows a clear correlation between audible echoes and decorated shelters,” says music archaeologist Riitta Rainio of the University of Helsinki in Finland, who did not participate in the new study.

Echoes that bounce off steep rock cliffs bordering three lakes in northern Finland also attracted ancient artists, Rainio says. She and her colleagues took acoustic measurements at Finland’s painted cliffs from 2013 to 2016. Microphones placed on boats positioned at different spots on nearby lakes measured sound waves generated, in most trials, by a starter’s pistol. These Finnish paintings date to between around 7,200 and 3,000 years ago, Rainio says.

In some cases, echoes reflect directly from cliff paintings. “That, and possible drumming figures painted on the cliffs, suggest that sound played some role in rituals at these sites,” Rainio says. Her team will report its findings in an upcoming Journal of Archaeological Method and Theory.

Creators of older Stone Age cave art also appear to have focused on sites where echoes abounded, says archaeologist Paul Pettitt of Durham University in England. For instance, many roughly 14,000- to 12,000-year-old animal drawings and engravings at France’s Niaux Cave cluster in a cathedral-like chamber where sounds echo loudly.

“The new study provides convincing evidence that echoes, which were scientifically inexplicable to prehistoric people, played a determining role in how art was created,” Pettitt says.

Big, rogue planets — ones without parent stars — are rare.

A new census of free-floating Jupiter-mass planets determined that these worlds are a tenth as common as previous estimates suggested. The results appear online July 24 in Nature.

Planets can go rogue in two ways: They can get kicked out of their parent planetary systems or form when a ball of gas and dust collapses (SN: 4/4/15, p. 22).

In the new study, Przemek Mróz of the Astronomical Observatory of the University of Warsaw and colleagues estimated the number of large, rogue planets in our galaxy using a technique called microlensing. When an object with a mass of a planet passes in front of a distant, background star, the gravity of the planet acts as a gravitational magnifying glass. It distorts and focuses the light, giving up the planet’s existence.
Mróz and colleagues looked at 2,617 microlensing events recorded between 2010 and 2015 and determined which were caused by a rogue planet. For every typical star, called main sequence stars, there are 0.25 free-floating Jupiter-mass planets, the analysis suggests.

The new result sharply contrasts an estimate published in 2011, which suggested that rogue Jupiters are almost twice as common as main sequence stars. About 90 percent of stars in the universe are main sequence stars, so if that estimate were accurate, there should be a lot of free-floating Jupiters.

“That result changed our conceptual framework of the universe just a little bit,” says astronomer Michael Liu of the University of Hawaii in Honolulu. It challenged long-held ideas about how planets go rogue because the known methods wouldn’t generate enough planets to account for all the wanderers.

The 2011 result was based on a relatively small sample of microlensing events, only 474. Since then, infrared telescope images haven’t detected as many free-floating planets as expected. “Over the years, serious doubts were cast over the claims of a large population of Jupiter-mass free-floaters,” Mróz says.

David Bennett, coauthor of the 2011 study, agrees that the new census failed to find evidence for a large population of Jupiter-mass rogue planets. He notes, however, that the new data do reveal four times as many Jupiter-mass failed stars called brown dwarfs than predicted in the original census. So some of the rogues that were originally classified as planets may, in fact, be failed stars. Bennett, of NASA’s Goddard Space Flight Center in Greenbelt, Md., and colleagues are working on a new analysis of potential rogues with nearly 3,000 microlensing events and plan to compare their results with those from the new census.
Liu says the latest census is much more in line with theories of how planets form. Most rogues should be Earth-mass or a little heavier. Those lighter planets get tossed out of their planetary systems much easier than behemoths like Jupiter. Still, the smaller planets are harder to detect.

The new microlensing analysis did identify several events in which stars brightened and dimmed in less than half a day. Such short events hint at the existence of Earth-mass free-floaters because smaller planets with less gravity should brighten a distant star more briefly than more massive stars. Determining whether those small planets are really rogue and counting how many there are will take better telescopes, the team notes.

A species gets only one chance to explore its solar system for the first time.

For humans, that chance began 40 years ago this month, when the twin Voyager spacecraft embarked on their “grand tour” of the solar system. A new PBS documentary airing on August 23, The Farthest: Voyager in Space, chronicles their journey to send home the first close-ups of the giant planets and to bring a message about life on Earth to the stars.
Voyagers’ launch dates took advantage of a rare planetary alignment. In 1977, the giant planets — Jupiter, Saturn, Uranus and Neptune — lined up in such a way that a spacecraft could swing past all four in less than 15 years, stealing some gravitational oomph from each world as it went.

That lucky alignment happens only once every 176 years. When NASA’s administrator went to President Richard Nixon to ask for funding for Voyager, he allegedly said: “The last time the planets were lined up like that, President Jefferson was sitting at your desk. And he blew it.”

The Voyagers almost blew it, too. The first craft (Voyager 2, confusingly) launched on August 20, 1977. It experienced so much shaking that its onboard computer — which had as much computing power as a modern car key fob — thought it was failing and put itself in safe mode.
Engineers got it back on track and fixed the problem for Voyager 1’s launch. Then that spacecraft’s rocket had a fuel leak during launch. The craft was within 3½ seconds of running out of gas before it accelerated enough to reach Jupiter.

These nail-biters are mostly told through personal, entertaining anecdotes from Voyager team members. Historical footage from press conferences and newscasts grounds the story in its era. Everyone has big ’70s computers and big ’70s hair. Cuts from shots of the scientists today to their younger selves emphasize how much time has passed. It’s strange that such a high-tech and ambitious mission seems so vintage.

Even the Voyager footage of Jupiter and Saturn coming into view for the first time has a home video quality, especially compared with the sharp, colorful images that spacecraft send back from these planets today. Watching the footage felt like watching video of my parents’ wedding: I recognize everyone, but they look so different.

But the sense of awe that the Voyager images sparked is palpable. At the time, every picture was the best planetary picture ever taken. Much of what is known about the outer solar system now — Jupiter’s moon Io has volcanoes, Europa has an ocean, Neptune has a great churning hurricane that never stops — was glimpsed for the first time with Voyager.

The Voyager spacecraft are still out there, and one may have already left the solar system (SN: 8/23/14, p. 6). Good thing because both craft carry a message in a bottle: the Golden Record.

The Golden Record was a literal record to be played on a phonograph by any aliens that might encounter the spacecraft. The package included a needle, a speaker and graphical instructions on how to play the record. A listener would hear a two-hour sampling of sounds from Earth, including babies crying, whales singing, chimps screeching, trains, thunderstorms, Beethoven, Chuck Berry, greetings in 55 languages and astronomer Carl Sagan’s son saying, “Hello from the children of planet Earth.”

The Farthest weaves the story of exploration with the story of the making of the record. The record’s producers and champions recount how they pulled the whole thing together in just six weeks. What to leave in — a map to Earth, in case the aliens want to visit — and what to leave out — full frontal nudity — was fiercely debated.

At times, refrains of “Wow!” and “It was a first” feel repetitive. Some of the stock footage and spacecraft animations are a little cheesy. But The Farthest is a tender tribute, tinged with nostalgia and existential awe. For those like me, who weren’t alive or aware when the first pictures of Jupiter came back, The Farthest offers a sense of what we missed.

As luck (or exceptionally precise astronomical modeling) would have it, my new, small Oregon town happens to lie in the upcoming eclipse’s path of totality. For nearly two glorious minutes on August 21, we will look up and see the unworldly sight of the moon completely blocking the sun.

To put it mildly, Oregon is going bonkers. Local radio is warning of gas shortages and apocalyptic traffic. Schools and businesses are closing. Emergency services are ramping up for the expected onslaught. Every local store has a pile of eclipse glasses near the register, yours for a very reasonable $2. (Oregonians don’t price gouge.)

I bought glasses (the good kind) for my family and put them in a high drawer. But as a parent to a 2-year-old, I realize that my eclipse prep can’t stop there. I’ve seen what the girl does to regular sunglasses, so I’ve got a few ideas to preschooler-proof these eclipse glasses for her.

Except for during the brief window of totality (when the sun’s surface is completely blacked-out), you shouldn’t look directly at the sun during an eclipse without wearing proper, eclipse-specific eyewear. The powerful light can cause extensive, sometimes permanent eye damage, a condition called solar retinopathy.

As you may imagine, it might be hard to impress this risk on children. Take the cases of these three Australian kids. After watching the 2012 partial eclipse of the sun through binoculars, a 10-year-old boy hurt his eyes. Examinations three months after the injury revealed persistent damage. Another boy, this one 8 years old, stared at the same partial eclipse directly. His eyes showed signs of harm five months later. And an 11-year-old girl who peeked at the 2012 transit of Venus with only her right eye also suffered persistent eye damage.

Those cautionary examples, described in 2015 in the Journal of the American Association for Pediatric Ophthalmology and Strabismus, made me want to duct tape my children’s eclipse glasses to their heads, mummy-style.

In lieu of that, I’m opting for super thick and stretchy fabric bands that I’ll staple and tape to the arms of the glasses. I’m also experimenting with a headband to limit movement on the top of the head, and perhaps even a paper plate taped around the front of the glasses to block incidental light. You could even take a note from 1963 schoolchildren, who put big boxes over their heads to see a projection of an eclipse.
I was happy to see that my DIY ideas aren’t totally off: Amid its wealth of eclipse information, the American Astronomical Society recommends modifying eclipse glasses with elastic or tape around the back so they sit firmly on small faces.

Of course, if you have a little Houdini who regularly squirms out of constricting clothes, you may consider any tweaking to be too risky. A simple pinhole projector, which doesn’t require looking anywhere near the sun, might be better.

Clearly, eye protection is something to take seriously. But don’t let that worry keep you and your children from seeing this once-in-a-lifetime celestial event. It’s the type of natural phenomenon that people — especially really young ones — can grab onto and understand. After all, kids love shadows, and this is going to be one heck of a shadow.

"It's the worst possible news on the eve of the tournament," said England midfielder Izzy Christiansen to BBC Sport. Spanish football journalist David Menayo called it "a jug of cold water" thrown over his nation.

They were referring to the loss of Alexia Putellas, who suffered a torn ACL on the eve of this the women's Euro 2022 tournament, leaving Spain without their reigning Ballon d'Or winner. The loss of such a superstar was evident, as Spain, a pre-tournament favorite, looked tame in bowing out to England in the quarterfinals.

Just a week later, young France star Marie-Antoinette Katoto suffered a similar fate in the Euro group stage, and a toothless Les Bleus attack fell short in the semifinals to Germany.

Bright young USWNT star Cat Macario, who lit up the Champions League for Lyon en route to winning the title over Putellas's Barcelona, tore her ACL in the early stages of a meaningless Ligue 1 match in early June. Two weeks later, legendary American striker Christen Press tore her ACL during NWSL play with expansion club Angel City FC. Just a month prior, Macario's Lyon teammate Dzsenifer Marozsan suffered the same fate, ruling the German star out of the Champions League final and leaving her sidelined for the Euros.

It doesn't stop there. USWNT defender Tierna Davidson went down in March of 2022 with an ACL injury during a shortened NWSL preseason. The Australian national team lost three players to ACL tears in a year's span, including young superstar Ellie Carpenter, who has already collected a massive 57 caps at just 22 years old, but went down in late May. A similar rising star for the German national team, Giulia Gwinn, suffered the injury in early October of 2021, her second ACL tear at just 23 years old.

As time progresses, the list just continues to grow — NWSL finalists Kansas City Current saw midfield fixture Claire Lavogez fall victim in the 2022 playoff quarterfinals. In the run-up to the 2023 Women's World Cup, stars Beth Mead and Vivianne Miedema both suffered ACL tears that ruled them out of the game's biggest event.

"The amount of ACL injuries in professional women's soccer in the last two years has just been shocking," Christen Press told ESPN in May of 2023. "If this happened on the men's side, we would have immediately seen a reaction of 'how are we going to solve this and figure this out, and make sure that these players are going to be available at the biggest moments of their career?'"

This is not just limited to the top of the game; clubs and college programs across the United States are noticing an increase in serious knee injuries. The Wake Forest women's team, a top ACC Division I program, has suffered six ACL tears in the past year, an increasingly common struggle for NCAA women's soccer coaches to navigate.

ACL tears have always been a danger in both men's and women's football, but as top players across the women's global game began dropping like flies, The Sporting News began asking questions. It turns out, there are scientific reasons to explain the wave of ACL tears that strike women's soccer.

Women soccer players more prone to ACL tears than men?
Over recent years it has become mainstream knowledge that women are, quite simply, more prone to serious knee injuries than men.

Slight anatomical differences between men's and women's bodies, largely concerning variations in hip structures, leave women at a higher risk of ACL tears or other serious knee damage. "These are trends that we've seen in the sports medicine world for years now," said Dr. Howard Luks, Chief of Sports Medicine and Arthroscopy at New York Medical College and a 20-year orthopedic sports surgeon with over a thousand ACL surgeries under his belt.

"Women in general are at higher risk. They have various differences compared to male athletic counterparts."

Research published by the Yale School of Medicine shows that women are two to eight times more likely to suffer ACL tears than men. Due to a wider hip structure, the knees of females are angled slightly differently, putting more pressure on the ACL. The differences are incredibly slight, but the effects can be witnessed over long periods of time.

"The ACL sits within a narrow notch on the inside of the knee joint," Dr. Luks noted. "That notch has more narrow confines in females, which can increase the risk of injuries."

While anatomical differences between sexes are a large contributing factor, there's another significant difference from males to females. There's medical evidence to support that women are significantly more prone to injury during their menstrual cycle. Given the private and personal nature of this information, research has not permeated the athletic community.

"Our ligament tissue changes based on the influence of hormones," Dr. Luks explains. "The best example of this is a woman's pelvis expands significantly due to the influence of hormones, but pelvis ligaments are not the only ones to change during the various cycles that occur."

Even with all the above, an individual's sex is not the only contributing factor in the ACL tears that occur with greater frequency in women's sports. Playing multiple sports, especially at a young age, can help.

"We've seen an increase in ACL tears due to single-sports participation," says Dr. Luks, explaining that repeated pressure in the exact same manner without variation over time can increase the risk of injury.

"The same stress on the same limbs in the same joints on the same ligaments month after month without any rest has an impact."

ACL injury prevention in women's sports
In recent years, women's soccer and other women's sports have sought to acknowledge the differences in injury risk, and to take steps to try and develop methods of prevention to counter the potential causes.

FIFA 11+ program

While there's no silver bullet when it comes to injury prevention, there's one program that stands out from the rest. The FIFA 11+ program was cited by multiple interview subjects for this report, and often without any prompting.

The FIFA 11+ program focuses on forcing athletes to build muscle memory for one key part of athletics, particularly soccer, that athletes often overlook: landing. The program is designed to be implemented as a short 10-minute warm-up performed before training and/or matches to positively reinforce proper landing techniques.

"They look at the way women jump and land on a surface, and what happens in their knees and ankles," says Brian Maddox, head athletic trainer for NWSL club North Carolina Courage. "They find that [women] move with more motion in their knees and hips when they land."

Dr. Luks, a proponent of the FIFA 11+ program, pointed to a superstar of the men's game for inspiration. "Watch Ronaldo when he lands on a header in the box. He lands on a flexed knee, the leg is as straight as possible, and when he lands he cushions the blow by going into a single-legged or a double-legged squat. These are all techniques that are taught [in the program] to diminish ACL ruptures.

"It's drilled into their heads," Dr. Luks explains. The idea being that such a simple action becomes healthy muscle memory. "Let's say you break your ankle, I put you in a cast, I take the cast off — your muscles are all atrophied. Half of that weakness is loss of muscle strength, but the other half of it is the lack of neuromuscular connections — your brain is no longer connected to those muscle fibers."

Dr. Luks' hypothetical metaphor is meant to show that building neuromuscular connections can create what we know as "muscle memory."

Wake Forest women's soccer senior defender Lyndon Wood, who serves as president of the school's Student Athlete Advisory Committee and is conducting her own research on ACL injuries in women's sports, said she brought the FIFA 11+ program to the Demon Deacons. It was quickly given approval by longtime head coach Tony da Luz.

"I felt like something needed to be done; anything we can do to keep one more girl on the field longer we should do," she said. "I brought it to [Wake Forest Sports Medicine program director] Dr. [John] Hubbard and Tony, and they were like 'Yeah, let's do it.'"

U.S. Soccer medical staff confirmed to The Sporting News that FIFA 11+ and other similar models are employed in training programs at all national team levels, although they would not dive into specifics of the programs at the different levels.

The FIFA 11+ program, however, still has yet to catch on everywhere. When Dr. Luks, whose three kids all play youth soccer, brought the FIFA 11+ program to the directors of their youth soccer programs and volunteered his time, they didn't jump at the opportunity.

"We went out to the schools assuming they would love it…no. Nobody wanted it. I can't explain it, and I was never given a good reason."

Special training regimens
The topic of a woman's menstrual cycle and how it affects injury risk in athletics is a sensitive one, and as a result, action has been slow in taking shape.

An assistant coach at a NCAA Division I women's lacrosse program in a Power 5 conference confirmed to the Sporting News that their program has just this season begun to track their athletes' cycles with the backing and participation from the players themselves.

With this information, women experiencing their menstrual cycle conduct separate, lower intensity training to minimize the risk of injury. It's not yet a practice that's widely adopted, and the same coach indicated that the women's soccer team at his school has yet to implement this same practice.

That's not surprising, says Maddox, the head trainer with the NWSL's Courage. "To my knowledge, it is not widely done in the U.S. because it can be a sensitive subject for some." Maddox says that he is aware of one top European club that does track their athletes' cycles, although he's not sure if they have yet to offer separate training based on the information.

It was widely covered following their 2019 Women's World Cup victory that U.S. women's national team players tracked their menstrual cycle throughout the four years leading into the tournament, and national team players publicly stated that there were several off-field programs implemented to complement this with regards to sleep and mental health. However, U.S. Soccer did not confirm whether these methods currently impact training intensity and injury prevention practices.

This may be the next step in the evolution of injury prevention in women's soccer if the USWNT's experience and that of other college programs yields positive results.

An assistant coach at another NCAA Division 1 women's lacrosse program confirmed to the Sporting News that their program suffered five ACL tears in the past year, and all five women were on their period at the time they were injured.

Mental health and injuries
In recent years mental health has gained increased attention throughout the athletics community, and its importance in injury prevention and recovery is being recognized as part of that push.

"Taking care of the athlete holistically…mentally and nutritionally, those resources are available to athletes these days when maybe they weren't as dialed in 15 or 20 years ago," says Maddox, who has prior athletic training experience in the NHL and minor league baseball.

"You can't disregard the mental aspect of it, this day and age every professional team across sports has those resources available to the athletes because it's useful."

When asked what she's learned through the recovery process, USWNT defender Tierna Davidson told The Sporting News, "Just to be patient with myself. It feels cheesy and simple, but I think as athletes we are impatient because we want results and we want to be 100 percent as quick as possible.

"But I think that through this process I have learned how to celebrate where I'm at in each stage, and not getting down on the fact that I suck at heading at the moment or I'm not as fast at the moment, or whatever it is."

A long way still to go
While more information is being gathered, some programs across the globe have been slow to implement change due to social and societal boundaries that are still difficult to breach.

"[ACL injury research] became a really hot topic in the late '90s and early 2000s," says Maddox. "That's when a lot of the research was conducted, specifically with regards to why women tear their ACLs more than men."

Maddox explains that strength training is a key part of injury prevention, but that the culture around women's sports doesn't lend itself to nearly the amount of strength training that is prevalent in men's sports.

"The way women are training from the youth on up…the emphasis in men's sports and boys sports is that you're not an athlete unless you lift weights. That culture is slowly hitting women's athletics, but it's behind the men."

When asked what they've learned in recent years regarding ACL tear prevention, the U.S. Soccer Federation didn't share any specific details or data points, except to confirm that it's top of mind with their programs.

"U.S. Soccer continuously builds loading programs for players. We work diligently with their clubs and/or universities in monitoring the players and develop individualized plans based on multiple factors in building out ACL prevention, but also soft tissue injuries as well. This has been a long-standing pillar for U.S. Soccer’s care of its players."

Why have so many women's soccer stars torn their ACLs?
The ability to pinpoint specific causes of injuries is ultimately an inexact science. When it comes to the human body, there are so many factors and variables that can affect an athlete's propensity or resistance to injury.

U.S. women's national team star Alex Morgan, who tore her ACL way back in high school, told The Sporting News during a USWNT press conference in the fall of 2022 that she thinks it's possible a shortened preseason and extended competition at the domestic level in the United States could be to blame for injuries in her part of the world.

"We look at the [NWSL] Challenge Cup, it was a great preseason tournament to have," Morgan said in early September in reference to the kickoff tournament of the U.S. women's professional season. "But having that bonus set for players to win, having it be a little more competitive than I think players were really ready for, having players playing 90 minutes week-in and week-out…is that the best for players in the first five weeks of the preseason? Probably not."

Dr. Luks says a quick ramp-up to competitive matches early in the season potentially increases the risk for injury. He explained how a proper and full preseason is critically important to avoiding injury during the year. Essentially, nerves that direct muscle movements connect to those muscles via "motor end plates" which degrade over time. Preseason, which features a slow increase in repetitive activity, is required to rebuild those connections.

"If you don't have connections to all the muscle fibers, I don't care how many weights you put on the rack, it's irrelevant, you're only exercising a third of the muscle fibers, because the other two-thirds don't have a connection to your brain, so they're not firing," Dr. Luks explains. "So that's such a critical component of a preseason program."

The Chicago Red Stars' Davidson, who suffered her ACL tear in preseason training in March 2022 before the Challenge Cup, was less convinced there was a common link in the rash of injuries that afflicted the stars of the women's game in 2022, but she acknowledged that an accumulation of minutes could potentially be responsible for her injury.

"I definitely think you can point to the volume and load that a lot of international players take through their club and country, so I'm sure that a bit of fatigue has to do with it. Sometimes it could just be coincidence, I don't know everybody else's schedule, but I do think there could have been some overuse of players."

A look at the numbers does support Davidson's suspicions. From January to November of 2021, the 24-year-old played 3,224 minutes across both club and international duty, including 1,780 minutes after the start of August. Add in three February 2022 national team appearances in the SheBelieves Cup, and with the short preseason ramp-up, she suffered her tear in March.

Many of the top international players injured this spring had similarly heavy loads. The chart below illustrate the range of matches and minutes played by some of the stars who suffered the ACL injuries (statistics via FBref.com).

Work load for soccer stars prior to ACL injury
(Note: Players listed below in alphabetical order.)

Player Date Range Games Minutes
Tierna Davidson Jan 22, 2021 — Nov 30, 2021 41 3,224
Giulia Gwynn Aug 29, 2021 — Oct 2, 2022 43 3,305
Marie-Antoinette Katoto Aug 5, 2020 — Jun 25, 2022 66 5,145
Catarina Macario Jul 1, 2021 — Jun 1, 2022 45 3,021
Dzsenifer Marozsan Jan 15, 2021 — Apr 12, 2022 70 4,893
Christen Press Oct 4, 2020 — Jun 11, 2022 36 2,686
Alexia Putellas Sep 19, 2020 — Jun 25, 2022 36 2,846
The table above shows 30-year-old Marozsan played close to 5,000 minutes across a 15-month period. So did 24-year-old Katoto, who logged 5,145 minutes over two years. Christen Press's numbers don't quite jump off the page, but what stands out is that she had little activity between mid-July 2021 before the Challenge Cup in March 2022.

The schedule congestion is not unique to these players specifically, but many top players across the globe are juggling busy club and international schedules that are increasing in load as the women's game explodes in popularity.

Alex Morgan, who's been a professional since 2011, ultimately labeled the rash of star knee injuries in 2022 an "unlucky run." But what is clear is that there are more variables that impact a women's soccer player's injury chances than in the case of a male player. And there's more research and information sharing that still can be done to investigate each of those factors.

Was it an unlucky run? We'll find out soon enough in the lead-up to the expanded Women's World Cup with 32 teams in July 2023. Given the names forced to sit out due to injury in the summer of 2022, a similar rash of injuries would not go unnoticed ahead of the biggest tournament in the sport.