Editor’s Note: This story is part of Peak, The Athletic’s desk covering leadership, personal development and performance through the lens of sports. Follow Peak here.
At 13, Jannik Sinner left home to train with a famed Italian tennis coach named Riccardo Piatti. It was the first time he had focused solely on the sport, and although he harbored big dreams, he stayed realistic.
“If one day I would have been top 100,” Sinner recalled, “I would be the happiest.”
He understood the odds, and he knew how expensive the sport would be. So he told his parents that if he was not in the top 200 in the world by the time he was 23 or 24, he would stop playing.
Considering where Sinner is now — world No. 2, winner of four grand slams and still just 24 — it would seem that he undersold his potential. However, Sinner did not have the usual tennis upbringing.
Born in northern Italy, in the German-speaking province of South Tyrol, he spent his early years as a competitive skier and dabbled in other sports. Until he began working with Piatti, tennis was only a part of his life.
Tennis, by form and tradition, is a sport of prodigies. The very best often pick up a racket as children, head to academy coaches by their 10th birthday and grind on the junior circuits for years. The pathway to success has long put the sport at the center of the youth sports specialization debate and the questions facing athletes and their parents: What is the best way to develop a young athlete? When is the best time to specialize?
Researchers say that specializing early — defined as training year-round before the age of 12 — can increase the risk factor for injury and hinder skill development. It can also hamper creativity and problem-solving.
According to a 2019 survey published in the Orthopaedic Journal of Sports Medicine, an estimated 45 percent of Division I athletes in the United States played multiple sports until the age of 16. But that means more than half of them specialized before the age of 16, and despite decades of research on the subject, experts say the numbers are holding firm.
“It’s actually very difficult to change this cultural phenomenon that we have with youth sports,” said Dr. Neeru Jayanthi, a sports medicine physician at Emory University.
Jayanthi has spent the last two decades studying the development of young athletes. To date, he says, there hasn’t been a single study that shows that specializing in a single sport in early childhood offers an advantage compared to multi-sport play. Instead, researchers tout the benefits of sampling — acquiring a diverse set of skills through different sports.
Of course, there is no single path to athletic success, and every sport has its unique demands. Most golfers pick up the sport from a very young age, while most top NFL quarterbacks played multiple sports in high school.
Michael Phelps initially wanted to play youth football, but his mom encouraged him to consider specializing in swimming; he went on to become the most decorated Olympian of all time. Patrick Mahomes played on the baseball team for a short time in college; he became an MVP and a three-time Super Bowl-winning quarterback before turning 30.
When it comes to making recommendations for millions of kids around the world, Jayanthi believes something else, too: Skiing probably did make Sinner a better tennis player.
But there is much more for parents to consider.
Jayanthi stumbled upon the issue of sports specialization by accident.
A trained orthopedist, he was examining injuries in youth tennis players in the mid-2000s when he and his colleagues discovered an interesting connection. In a study of 530 high-level tennis players aged 12 to 18, approximately 70 percent had specialized in tennis by around 10 years old. The group was 1.5 times more likely to report injury than those who hadn’t specialized.
Jayanthi wasn’t overly confident in the data set, but the paper, published in 2009, was the first to associate sport specialization and injury risk. It also came out the same year that Andre Agassi published his memoir, “Open,” which detailed the pressures of youth tennis.
The study spurred additional research, which confirmed the link between specialization and injuries. It also led to pushback against increasing specialization in all youth sports, which put a focus on those who defied the trend. It’s not hard to find examples of athletes who benefited greatly from a diversified childhood of many sports.
Before New York Yankees star Aaron Judge won multiple MVPs, he was a three-sport athlete in California, sticking with basketball and football throughout high school. For most of Mahomes’ childhood, football was his third-favorite sport. The son of Pat Mahomes, an MLB pitcher, Patrick excelled on the baseball diamond and found joy on the basketball court with friends. He didn’t become a starting quarterback until midway through his junior year of high school.
When he did fall in love with football, his sampling experiences influenced his play. Thanks to basketball, he possessed impeccable spatial awareness. Thanks to baseball, he mastered the art of throwing from awkward positions and unconventional arm angles.
“That’s playing shortstop,” Mahomes once said.
For researchers, the story of Mahomes is a clear example of what they call “adaptability,” a variation on the concept of cross-training.
“There’s a transfer of skill,” Jayanthi said. “You don’t overload the same body parts every time. And there’s also an element of fun, of problem solving and variety.”
Science reveals other advantages. Gregory Myer, director of the Emory Sports Performance And Research Center, has studied neuromuscular training and biomechanics. When an athlete samples multiple sports at a young age, it’s not just about utilizing and building a diverse set of muscles. There is also a cognitive benefit.
The process of acquiring diverse skills, Myer says, creates adaptability in the body and what he terms “neural efficiency” in the brain. One result: According to a virtual reality study conducted at Emory, multi-sport athletes were found to have better motor control and landing skills.
“If a young athlete specializes before they get a good sports sampling early in youth, they’re not developing those requisite motor skills that are diverse,” Myer said.
Still, an interesting development occurred in the 15 years following the publication of the original study. Despite the links to injury risk and the high-profile examples in sports, the overall numbers haven’t changed. Kids are still specializing in sports at the same rates.
Jayanthi and Myer use a simple framework to define sports specialization, asking three questions:
Does the athlete train for one sport more than eight months a year?
Does the athlete choose one “single main sport”?
Did the athlete quit all other sports to focus on one?
Athletes who say yes to all three are considered “high” specialization, while those who qualify for two are “moderate.” The rest are considered “low.” Researchers estimate that each group roughly represents about a third of the young athlete population in America, which is the same proportion as when Jayanthi began his work.
If the numbers were not going to change, Myer had another idea: Perhaps there was a way to specialize thoughtfully.
“We shouldn’t be dogmatic in the way that you say, ‘You can’t do this or handle this,’ ” Myer said. “What we need to do is, if there are kids that are going to specialize, how do we help them?”
In the years after the initial studies, researchers developed guidelines for coaches and parents. It’s recommended that young athletes not train a single sport for more hours per week than their age. And when it comes to team sports, Jayanthi advises that girls not specialize until at least ages 11 to 13, while boys should wait at least until ages 13 to 15, allowing the body to mature skeletally.
It also depends on the sport. When it comes to activities based on raw strength and speed — such as football or basketball — it is possible to specialize around the age of 16 to 18 and reach the top of your sport. In sports that require more technical skills, such as tennis, golf or baseball, it may make sense to specialize in mid-adolescence.
There are exceptions: Take gymnastics, a technical sport where athletes often compete before they’re fully mature. In instances of early specialization, Myer says, it’s critical to adopt training methods that mimic other sports and movement patterns to decrease the risk of injury.
At one point during his research, Jayanthi also began to ponder the true meaning of youth sports. Was it to have fun and learn life lessons? Was it a matter of public health? And what about the kids that had no realistic chance to play professional or even college sports but might benefit from the confidence boost inherent in making a team? What if they needed specialized training to do that?
“If your goal is to be the best 12-year-old in the neighborhood,” Jayanthi said, “then start them when they’re 6, train a lot and then get them to be the best 12-year-old. And you actually have a reasonable chance.”
Jayanthi refers to this as “short-term athlete development.” It may not help an athlete reach their full potential in the long term, and it comes with its own inherent injury risks. However, in the short term?
“It actually works,” Jayanthi said. “Sadly.”
When Sinner has reflected before on how skiing influenced his tennis, he has mentioned his balance, which manifests in sensational body control and movement on the court. Despite being a sinewy 6-foot-3, he is one of the best movers on tour.
But he believes the real benefit was how it helped him cope with failure. If he made one mistake in skiing, he could not win the race. In tennis, he can make numerous errors and continue fighting back.
“You have a completely different mentality by skiing,” Sinner said.
Jessica Pegula, the world’s seventh-ranked women’s tennis player, grew up playing a variety of sports. She tried organized softball, played soccer and took golf lessons between the ages of 7 and 10. At the age of 11, she began to focus solely on tennis.
The early sampling, Pegula believes, likely laid the groundwork for her hand-eye coordination. However, when she considers the late-blooming arc of her career — first WTA title at age 25, first Grand Slam final at age 30 — she probably could have held off on specializing. Still, the pressure to excel in juniors was clear.
“I probably could have gone a few more years and I don’t think it would have had a huge impact,” Pegula said. “Looking at my career, I didn’t really do as well until later. But I think by the time you’re 12, 13, you have to kind of commit to playing tournaments and getting rankings.”
Pegula’s path underscores an overlooked aspect of the specialization question. It’s not just that young kids are specializing earlier. It’s that almost all of their sporting experiences from a young age are in an organized environment.
“Playing for fun on their own has become culturally lost,” Jayanthi said.
In previous generations, a majority of sports experiences were found in casual, unorganized settings. Now the reverse is true. American kids spend twice as much time in organized sports as playing for fun. Research has shown that increased free play is a determinative factor in protecting against injury. It also helps develop better motor skills and increased creativity.
Among many parents, a persistent fear remains that their children will fall behind.
When Greg Olsen, a former NFL tight end, retired in 2021, he launched Youth Inc., a platform focused on young athletes and their parents. His experience colored his interest — he has three young teenagers entering a vastly different sporting landscape, surrounded by societal pressures and a corporatized culture.
“What the kids feel,” Olsen told The Athletic’s Elise Devlin recently, “is that it’s very hard to walk into every season to a new sport and compete against kids who have only been doing that sport for the last 12 months.”
Olsen believes the mindset misses a crucial point: One of the best ways a talented athlete can grow is to not be good at something. Every sport offers a distinct culture, skill set and fresh mental challenge.
When a star football player spends his winters as a role player on a basketball team, it can physically challenge him while providing an essential perspective on teamwork. It’s not just the adversity; it’s a chance to problem-solve.
“Each one of those unique sports offers such a different environment for them to learn, for them to fail, for them to have success,” Olsen said.
For many researchers, the concern is that kids who do not have a sample period will miss out on what could have been their best sport. The truly elite often do not reveal themselves until after puberty, and the combination of early specialization and a lack of unstructured play is one reason Myer has a bigger worry: rising rates of non-participation.
“To me, quitting a sport early is our biggest risk factor because now we’re losing that opportunity to create healthy physical activity and sport participation for the rest of our lives,” Myer said.
For Jayanthi, who leads Emory’s Tennis Medicine program and has advised the WTA, the stories of Sinner and others have shaped his perspective on athletic development. In sports like tennis, an extreme level of practice volume is required. In reality, it leads to earlier specialization. However, those players who spent their childhoods diversifying their skill sets may be best equipped to handle the load.
“The better model might be: Build the athlete first,” Jayanthi said. “You can tolerate the volume and load when you’re a little bit older and skeletally mature. And that’s when you can ramp it up.”
According to Jayanthi, there will always be athletes on different paths. If he were making recommendations for kids across America, he would suggest being patient, sampling different sports, building up a diverse set of skills and focusing on having fun.
“But there will be a subset that will continue to specialize,” Jayanthi said. “And of that subset, some of them will be really successful. Because they are the outliers.”
(Illustration: Dan Goldfarb / The Athletic; iStock)
