A 3-YEAR-OLD BALL of energy named Noah bounds around a former live music venue one block from the beach in Santa Barbara. He's surrounded by about a dozen top prep prospects from around the U.S., all here at P3 Applied Sports Science, a performance lab that has assessed the biomechanics of hundreds of the world's best athletes, including about 350 NBA players over the past 11 years.

It's the first Saturday morning in May 2017, and Noah is here with his older brother, Zion, who fears that Noah will one day be better than him, because Noah began playing basketball at 2 years old while Zion only started at 4.

For now, though, Zion Williamson is 16, and in one month will grace the cover of Slam magazine, which will state that the 6-foot-7 forward is as explosive as Russell Westbrook and can dunk like LeBron James.

At P3, basketball players are typically outfitted with 22 markers, each 12.7 millimeters in diameter and placed on a dozen specific anatomical landmarks, from their feet all the way up to their back. After warming up, they undergo a series of vertical and lateral movement tests atop two force plates installed in the floor beneath them, which record their ground reaction forces. Looking on are 10 3D motion-capture cameras, at a multitude of angles, capturing more than 5,000 data points, including joint-by-joint kinetic and kinematic information. The assessments take 15 minutes. A half hour later, a remarkably detailed biomechanical model of each athlete's skeletal system is produced.

Today, P3 officials are eager to assess Zion, given his off-the-charts athleticism and the gravity-defying slams that have already made him an international viral sensation. But instead of taking such tests, Zion is spending his first P3 visit focusing only on recovering from another long season of club basketball that, his parents worry, has taken its toll.

Those parents, Lee Anderson and Sharonda Sampson, stand nearby while Zion's legs are swaddled in Normatec sleeves. As the sleeves swell with air, compressing muscles to improve blood flow, Lee and Sharonda recall their own athletic experiences. Lee played college basketball at Clemson; Sharonda ran track at Livingstone College in Salisbury, North Carolina. When they were kids, decades ago, athletes played several sports and took summers off.

Zion, however, began playing on youth basketball teams at 5 years old, competing against those twice his age, and he's been playing on the travel circuit ever since. These days, his school season starts in October, then he rolls into summer youth basketball. "This is all he does," Sharonda says, as she watches her son. "He doesn't have time for anything else."

During the summers, he'd play four games in a weekend, maybe even five or six, then train for hours every day during the week. Before they knew it, Friday would roll around and he'd be off to play in another tournament. Recently, though, Zion has been feeling the brunt. After bouncing from Las Vegas to their home in South Carolina, then back to the West Coast for events, games and training, soreness and fatigue have seeped in. The high school junior says he felt especially haggard after a recent Adidas event in California, where cramps and charley horses wracked both of his legs for an hour, a first for him.

Years ago, Sharonda might have told her son to toughen up. But as Zion's basketball profile has risen (he just averaged 36.8 points and 13 rebounds in his junior season while leading his high school to its second straight state title), and as she and Lee have become exhausted just from attending his games ("We know if we're wearing out, he's wearing out," she says), she listens more. Sharonda carries a degree in health and physical education, but she's also studying kinesiology -- the science of body movement. Today, if Zion says he's tired, she asks him to take time off.

At the moment, Zion, still in his Normatec sleeves, is recovering from a bone bruise he suffered a month ago during an AAU game in Arkansas. It was a humid night, and the floor was wet, so Zion kept slipping, hitting his knee on the court. He awoke the next day to find it swollen. Two weeks' rest was prescribed, but the moment, Sharonda says, provided a realization: Zion is 16, she thought to herself. He has way more basketball on the other side, way in front of him.

Zion says he gets it -- sort of. "That is going to be your money-maker, your body -- so we have to start taking care of it," his parents tell him. They point to the NBA, where he aims to play for at least a decade, and where recent seasons have been dominated by discussions of rest and players sitting out. "They're resting," his parents say. "You should be resting, too." But the other half of Zion wants to play.

But then, as Zion is explaining his desire to play more, Lee cuts in.

"But we're not going to let him do it when he's hurt," Lee says. "We're not going to let him do that ... as parents we're going to actually let him know, Hey, you shut that down until you get better."

Early on, Zion's parents felt the pull of the youth circuit, as if attendance were required and missing it meant missing out on a future in the game. But as Zion got older, his parents fielded more requests for him to appear at tournaments and events. So earlier this year, they decided to limit him to four per summer.

Here, in the high-tech sports science lab, Sharonda looks at her son -- at all the promise before him. How can she get the message through? "You're 16," Sharonda tells him. "In 10 years, you'll be 26. You don't want to be worn down by the time you're 26."

THE ORTHOPEDIC SURGEON leans over the right knee, two dime-width incisions already sliced on each side. Now comes another, just behind and below the knee -- this is where he'll draw out a shiny tendon that looks like a fresh shoelace dipped in cream: a hamstring. There are four such tendons to choose from, and they will grow back within nine months, but the surgeon only needs two. They will be used to help replace the torn anterior cruciate ligament in the knee -- an injury suffered on the football field when its owner, during a game with friends, planted his right foot and collapsed.

A fellow in training and a scrub technician stand beside Dr. Nirav Pandya as he steadily guides the scalpel and maneuvers an arthroscope -- a small tube with a camera at its end -- inside the knee, sending back footage onto two flat-screen monitors nearby. His 39-year-old hands move with the efficiency and certainty of someone who has performed this procedure 600 times before (which he has). The steady beep of a heart-rate monitor fills the operating room. A ventilator hums while the patient's chest rises and falls. Outside, a grey sky spits rain on a late winter Tuesday afternoon in Walnut Creek, about 20 miles from Oakland.

Typically, a procedure to reconstruct a torn ACL might take 60 minutes for an adult, but this one is taking longer because the X-ray technician is wheeling over the machine after almost every maneuver and because each X-ray is scrutinized to make sure that nearby growth plates, which have not yet closed, are not endangered. Extra time is also taken to ensure that the meniscus, the cushion of the knee, is repaired to prevent the early onset of arthritis. These steps would not be taken on an adult who has stopped growing, but this is not an adult.

It is a 9-year-old boy.

Years ago, as a 10-year-old growing up in Chicago, Dr. Pandya had planned to follow his father, a family doctor, into medicine -- in his case, specifically to become the Chicago Bulls' team doctor. During his residency training in Philadelphia, Pandya decided that he wanted to work with kids. And seven years ago, he moved to the Walnut Creek branch of the UCSF Benioff Children's Hospital, which examines patients up to age 25. But one day, about five years ago, in came a new patient: an 8-year-old boy, a local basketball player who had ruptured his ACL.

"He was this kid who was basically playing four or five days a week," Pandya recalls. "He was doing drills all the time, and he was playing and landed wrong." His ACL popped. Pandya couldn't believe that such an injury could happen to someone so young.

In the years that followed, Pandya says, more kids that age began to come in, and the operating rooms filled with surgical trainees who came to watch because they had never seen such injuries to kids. But, in time, it became so commonplace that soon the shock wore off -- no longer did an ACL surgery to an 8-year-old raise eyebrows, nor did the constant stream of patients so young seem unusual. Five years ago, Pandya estimates that he alone would see about 1,500 pediatric sports injuries and perform maybe 150 surgeries -- ACL, cartilage, shoulder injuries -- in a single year; those numbers have "skyrocketed," he says, and last year stood at 6,000 and 400, respectively. More than half of his operations are now on those under the age of 14.

Often, Pandya says, he knows exactly what he'll find before ever making an incision, before the arthroscope reveals what's beneath the surface. He can roll the knee in his hands, and it might feel loose, like a bunch of untethered parts. He knows he'll see cartilage that should look paper white but is grayish -- not smooth, but rough -- not hard and solid, but soft and spongy. He knows he'll see an ACL and it will it not look intact, like a new shoelace, but frayed, like it's been through a meat grinder.

During the procedures, Pandya is focused on each step, knowing the pitfalls -- avoid hitting a nerve or blood vessel, be precise when drilling through bone to create a small hole through which to thread the new tendon. On the 15-minute drive from his home in Oakland to the clinic, he mentally prepares himself. How will the kid respond? How will the parents respond? Will each side listen? Will they take the rehabilitation seriously? Will they take the proper steps and be diligent?

Sometimes, he'll see kids who aren't injured but are in pain, month after month. "Look, you just need to stop," Pandya will tell the parents, "if you play 40 hours a week of basketball, you're going to get injured."

Time and again, though, the first question parents ask is not about the well-being of their kids, but simply, "When can my kid get back out there?" Pandya will explain the potential hazards of the surgery, including risk of infection or re-injury. He'll show them a picture of what a healthy knee looks like for someone of their child's age -- and then show them what their kid's knee looks like now: routinely worn to the point that it appears three decades older than it should.

But often, he says, the only time parents appear truly shocked is when they're told how long their child will be sidelined.

Pandya sees the kids throughout their rehabilitation process. Some he's seen for years; he reconstructed their ACL only for it to be torn again. In some cases, he has repaired their ACLs three times by their early teenage years. The parents drop the kid off for physical therapy almost every day, but the kid lives with the injury, the rehab, every single day. Sometimes, they'll confide in Pandya.

Look, I don't want to go back, the kids will tell him. I'm afraid of going back. I don't enjoy it anymore. I've spent my past three years just rehabbing. That's all I do. I go from one surgery to the next. I just want to be a kid.

Today, when he leaves the operating room, Dr. Pandya removes his surgical mask. He's 5-foot-6 and lean, a former collegiate track athlete at the University of Chicago. He's just finished his second ACL reconstruction surgery of the day; he does up to four a day now, two days a week. Earlier this morning, he reconstructed the ACL of a 12-year-old boy, a skier. The day before, another ACL, that of another 12-year-old boy, a soccer player. He heads to his office, takes a seat and resets for a minute.

"I don't want kids in my clinic," he says. Pandya thinks of his own children, a 7-year-old boy and a 4-year-old girl. His son loves sports, plays soccer, basketball, kickball and swims. And there may come a day when his children decide to focus on one sport, believing they need to specialize in order to stand out. Pandya knows he will then have to explain in detail what he sees at work almost every day.

IT'S ANOTHER SATURDAY morning at P3, in 2017, and E.J. Montgomery, a 6-foot-10 forward from Florida, settles into a chair behind a desk and peers at animated versions of his skeleton on a pair of computer screens.

Beside him is Eric Leidersdorf, P3's director of biomechanics, who is about to explain how Montgomery, a five-star forward in the class of 2018, scored in his assessment and how those numbers compared to the most elite college and NBA players. E.J. has gained seven pounds since he was last assessed by P3 nine months ago -- and his vertical leap has increased by four inches. But his ankles and quadriceps are tight, hampering the fluidity of his movement in a key area -- his knees. "The goal," says Leidersdorf, a scruffy-bearded Stanford grad, "is to make those things feel as good as new, back before you started playing crazy AAU schedules." E.J. nods. He's been playing club basketball since the fourth grade, 30 games a summer, plus 30 more during the school season. And in the years since, his father, Efrem, has seen it all: kids specializing early, accruing mileage.

E.J. is here along with 14 other players around his age. The players start cycling through workout stations where not a single basketball is present, warming up through a series of hops, skips and lunges before proceeding to vertical and lateral movement tests and a mobility screen where range of motion on their hips and ankle are measured with a digital protractor.

Then it's time to review the results. A combo guard from Texas is told he has tight ankles and needs to improve his hip mobility but that he jumps really well for his age, especially in comparison to most NBA shooting guards. "Now we just want to make sure you can do that for a long time," Leidersdorf says. A center from Senegal by way of Texas is shown slow-motion footage of how his knees bend inward when he jumps. He quietly asks what he can do to stop that. "We've seen way worse than this," Leidersdorf assures him. "It's just making sure it's good moving forward."

Adam Hewitt, P3's director of operations, stands nearby as players are given their results. "The AAU schedule is probably not going to change," he says, "but what you can do is make these guys better at withstanding the demands of playing so much. We can provide them with that. We can quantify and understand their inefficiencies so they can address them and become more well-rounded so they can go play every weekend and have a body that will still work."

While E.J.'s latest results are being explained, Marcus Elliott, P3's founder and lead scientist, is standing nearby. Elliott points at the animated version of E.J. on the screen, set alight by the markers. He explains how well E.J. moves laterally, then unspools a cautionary tale.

About five years earlier, Elliott says, P3 examined a 26-year-old NBA forward. "Look, the way you're loading across your right side, you're doing three distinct things that put stress on the medial aspect of your right knee, and you're likely going to wear out the cartilage on the inside of your right knee," P3 staffers told the forward at the time.

But then the P3 staffers learned that the player had no cartilage in that knee -- at all. It had completely worn out. "If we had gotten him earlier, the things that he showed us that were a problem were entirely preventable," Elliott says. "So that was one of those touchpoints. ... I was like, 'What if we got those guys not when they were 28 but when they were 18 or 17 or 16?'" That led to P3 to begin evaluating players like E.J., now being assessed for the third time. His first assessment came when he was just 14, making him one of the youngest players P3 has ever assessed. At one point, Elliott taps E.J. on the shoulder. "You don't want to go limping into this next phase," Elliott tells him. "I know you've got the skills to keep playing this game for a while, but your body has to be there, too."

E.J. smiles, revealing his braces.

"They shouldn't be peaking at 16 or 17," Elliott says later. "But I can tell you from a data standpoint, you can make a case for it. And you talk to the individual athletes, a whole lot of them will tell you, 'Oh, when I was a senior in high school is when I was jumping my best. I was moving my best.' A lot of guys will tell that story. It just shouldn't be that way. It should happen at 23, 24, 25, but with most of these kids, that's not the case."

STANDING IN THE middle of P3's facilities one afternoon after a flurry of prep players file out, a man named Jeremy Russotti surveys P3's high-tech gadgetry.

Russotti, co-founder of a prep basketball program that trains elite athletes, majored in kinesiology at Sonoma State -- and loves basketball. And after 14 years teaching middle school physical education, then working as a skills trainer/strength and conditioning coach for youth players, Russotti married his two loves at Prolific Prep, a program in Napa, California, that partners with Napa Christian, a private school. In 2014, with backing from Adidas, Russotti helped found that program in part because of issues that he saw around the youth landscape, where he says players were too often exhausted by marathon schedules, didn't receive proper training and saw promising careers be cut short because of it.

"[Basketball] is all he does. He doesn't have time for anything else." Sharonda Sampson, Zion Williamson's mom, in May 2017, before his senior year of high school

He vowed to do better: He would hold shorter practices -- not two hours a day, five days a week, as it was when he went to high school, but just 50 minutes a day, total. He also wanted to limit the number of tournaments and games that his players would play in, even if it meant taking heat from tournament directors, which he says happened when they sat one of their players, a future NBA lottery pick, for a dozen games during his senior year.

"We can see it in their body when they need a break," Russotti says. "We don't want to be the reason why a kid gets hurt."

The player they sat in those games? That star was forward Josh Jackson, who went on to play at Kansas and would become the fourth overall pick in the 2017 NBA draft. But to understand the depth of Prolific Prep's concern for player health, consider what Jackson heard when he'd practice acrobatic dunks:

"You just lost $1,000," Jackson was told. "You just threw it away from your future." Staffers would explain to him how leaping and landing impart a violent force on a player's knees, and that if he wanted to get the most out of those knees, he should save those jumps until it really mattered. If Jackson jumped 10 times in a day, they'd tell him he lost $10,000. If he jumped 100 times that month, they'd say he cost himself $100,000. They'd tell him he was well on his way to losing millions and millions, just on jumping alone.

Such thinking sounds radical, Russotti admits. "The AAU coaches and the parents, we get it all the time: 'Why isn't he working out? Why is he doing this? Why are you giving him time off? No pain, no gain.' That's the old philosophy. So we get that pressure, but we have to tell them, 'Understand. Just please let us do what we know.'"

The players, he says, don't buck against Prolific's methods. "The kids get it," he says. "They want a break. It's exhausting. Some of these kids, because they're pulled [in so many directions] and they gotta go to Nike, they gotta go to Adidas, they gotta go to Under Armour, they got all these games, they got all-star games, and they're telling them if they don't do it they won't be in the McDonald's All-American game, or they're not gonna make the Jordan Brand game."

AN NBA PROSPECT lays flat on a table. Mike Roncarati leans over him, placing one hand on the player's left ankle, another on his left knee. Roncarati, the Atlanta Hawks' director of rehabilitation, guides the player's knee toward his chest to test its range of motion. He holds the knee as it bends, feeling for any restrictions or limitations. He'll repeat this method for at least seven other joints, ranging from the prospect's shoulder to his big toe. "I'm looking for red flags," Roncarati says later -- warning signs that the prospect might suffer a serious injury soon after reaching the NBA. It's May 13, 2017, a Saturday, at the Northwestern Memorial Hospital in Chicago, inside a curtained-off, 20-by-15-foot space. It's one of a half-dozen makeshift exam rooms in which Roncarati and three colleagues from the Hawks' medical and training staff are working, surrounded by health records, X-rays and other data. The prospect is one of several dozen in town for the NBA's annual pre-draft combine, where teams interview and assess the league's crop of incoming talent one month before the draft. And when prospects aren't doing drills or scrimmaging before team officials at a Chicago-area gymnasium, they're at this hospital, where NBA teams perform medical screenings.

The doctors alongside Roncarati are running through the prospect's injury history, administering orthopedic tests to identify the amount of joint or structural damage to cartilage, ligaments or joints. Meanwhile, Roncarati, through a general movement assessment, is focused on identifying certain issues that might manifest in the player's future, based on how he moves -- or doesn't. Roncarati is in his second season with the Hawks, after spending the prior two with the Warriors, and though today marks the first time he's taking part in the medical-screening portion of the combine, he's evaluated scores of prospects in recent years, often during individual pre-draft workouts at the teams' respective practice facilities. By now, he's no longer surprised to see aspects of how a player moves that cause him concern.

He expects to see knees that don't bend properly, or hips that can't fully move side to side, which means they can't properly absorb the force of a landing without causing stress to the joint structures of all their lower extremities. "For me, if I lie someone down on their back and they can't bend their knees 10 to 20 degrees as much as they should as a 20-year-old kid? It certainly doesn't give me much confidence that they'll be able to tolerate the loading of the NBA," Roncarati says.

"[Players] shouldn't be peaking at 16 or 17. But I can tell you from a data standpoint, you can make a case for it. It just shouldn't be that way. It should happen at 23, 24, 25, but with most of these kids, that's not the case." Marcus Elliott, founder and lead scientist at P3, a sports science lab that assesses the biomechanics of the world's best athletes

Today, Roncarati will examine more than 60 players, each for about five minutes, and will jot down asterisks next to four names -- players he'll tell Hawks management not to draft. Each player suffered an injury at a young age, had surgeries and, Roncarati says, returned to action before they were fully recovered.

A month later, the Hawks will draft none of them. It's far from the first time that's happened. It has, in fact, become what Roncarati and his colleagues call the "new normal."

STANDING BESIDE A court before his team plays its first game, Leo Papile pets his team's mascot, Cotton, a bread box-sized 3-year-old "Yorkie Poo" with a "team personnel" credential hanging around his neck. A stream of fans stop to say hello. Few people might know more faces in the cavernous gym than Leo, a fixture on the grassroots basketball circuit who founded the Boston Amateur Basketball Club in 1977 and has been coaching them ever since.

Today, Papile finds himself inside an airplane-hanger-sized complex called the LakePoint Champions Center, located in a small valley in the foothills of the North Georgia Mountains. Above him hang massive banner photos of Anthony Davis, Gordon Hayward, Ben Simmons and other alums of the Nike EYBL circuit, the world's most prestigious youth basketball league, whose latest event, featuring 40 elite teams, is in full swing.

Papile surveys the gym amid a symphony of squeaking sneakers, bouncing balls and shouting adults. He's 63 with a broad chest, deep tan and a touch of Boston in his tongue, and as he pets Cotton, Leo describes the modern state of youth basketball by referencing the Soviet Union -- notorious for testing boys and girls at young ages, then training them intensively for years in whatever single sport they tested well at, a militaristic approach aimed at winning Olympic medals. That system yielded results; the Soviet Union won the most or second-most medals of any country in every Summer or Winter Olympics that it competed in from 1952-1988. But it was also criticized for creating athletic robots. And here, at one of the hundreds of youth basketball events held every year across the country, Papile nods toward the culture before him. "It's the Soviet system -- times 10," he says.

As he talks, a slogan surrounds him, emblazoned on all manner of T-shirts, screaming from the chests of players, parents, everyone. The slogan is three words. And it is ubiquitous.

BACK IN 2011, a man named Jeron Smith was sitting in his cubicle at Nike's world headquarters in Beaverton, Oregon, when an email popped into his inbox. He had received a brief prepared by the company's global marketing team that would later be sent to their advertising agency, which would recommend a campaign.

Smith, a 25-year-old North American brand marketing specialist in his second year as a full-time Nike employee, read through the brief and spotted three words casually mentioned in a throwaway line.

At the time, the NBA was in a lockout. But the phrase drew upon the notion that basketball would persevere, no matter the court. NBA stars had dominated the Drew League in Los Angeles, had done the same at the Goodman League in D.C.; Kevin Durant had dropped 66 in a pickup game at Harlem's Rucker Park during an August visit there. And so the words had resonated. They felt authentic and organic. To Smith, they had the makings of marketing magic.

He pulled a few colleagues aside and ran the idea by them, seeking feedback. He called another colleague, taking his temperature. The idea kicked up the food chain; in time, a campaign was launched.

A Nike executive had once told Smith that if he were ever to be famous for something, do it early in his career -- and this slogan helped give Smith that fame. Soon after, he joined a global Nike campaign that brought him to Paris, Barcelona and London. In 2015, he left Nike to join the White House as a deputy digital communications director in the Obama Administration, before becoming the chief marketing officer at Stephen Curry 30 Enterprises, then the CEO of Unanimous Media, Curry's production company. And still, years later, Smith sees the slogan everywhere. Today, it is written in all caps, in large block text, above Nike's famous "swoosh" emblem. It speaks to youth athletes who aspire to reach the game's ultimate level. It haunts those who fear that too many young athletes are playing too much -- and breaking down too soon.

And on this day, as the next generation of NBA hopefuls sprint and pivot and leap and land, it calls out from almost every square inch of Champions Center:

BASKETBALL NEVER STOPS.