KATELYN TUOHY

In just two years at North Rockland High, the speedy sophomore has established herself as one of the fastest schoolgirl runners—in both track and field and cross-country—in history

THE FASTEST girl in the country can't sit still. She doesn't remember the last time she made it through a movie. She fidgets in class. Except for the few times she's been sick, she doubts she's gone 24 hours without exercise since she took her first steps. Even now, perched on a red bench in the hallway of North Rockland High in Thiells, N.Y., 16-year-old Katelyn Tuohy is playing with two hair elastics, threading them through each other and tying them together as she patiently explains her impatience. People are always telling her to relax, but she's not even sure how to. "I don't know," she says. "Maybe go for a walk or something."

Her ideal day begins with a predawn wake-up and a 10-mile run. Then grab breakfast, go for a hike and hit the gym. End by barbecuing with friends, get to bed early and do it again the next day.

Instead Katelyn is on this bench in the idle moments before she heads out to the track for her SI cover photo shoot. She has just finished her sophomore year and in a few days will jet to Los Angeles, where she'll be presented with the Gatorade National Female Athlete of the Year award. (Katelyn has already become the first athlete in the 33-year history of the Gatorade program to be named the top athlete in two sports nationally—in her case, track and field and cross-country.) Nearly every week there has been a banquet honoring her. It can be hard to keep track of her successes: This winter she had the nation's top indoor times for high school girls at 1,500 meters (4:23.38), 3,000 meters (9:05.26) and two miles (9:58.89). In January she set the U.S. under-20 female record for the 5,000 (15:37.12). Four months later she broke the 22-year-old girls' high school outdoor 3,200-meter mark, running 9:47.88. In June she won her second straight mile title at the New Balance Nationals with at time of 4:33.87, eclipsing a record that had stood for 36 years.

Katelyn has been running competitively since she was 12, a tiny seventh-grader staring up at high school seniors before the gun fired. She has won nearly every race she has entered. So, Katelyn, what's the farthest you've ever run? She steals a glance at North Rockland's outdoor track coach, Kyle Murphy. "I can't answer that when he's right here," she says, giggling. "I'm going to get in trouble."

That's because Katelyn's team, which includes her parents, Denise and Patrick; Murphy; and Brian Diglio, who coaches the Lady Raiders' cross-country and indoor track teams, expends a lot of effort trying to keep her legs fresh. If they tell her she can run 10 miles one day, she will negotiate for 11. If they instruct her to train six days per week, she will ask to add a light run on the seventh. Even the workout pace offers a chance to haggle. "I've learned to give her times that are a little slower than I want her going," says Murphy, laughing.

Many high school runners have to be persuaded to work hard. Katelyn has the opposite problem. (Her mom occasionally has to beg her to put aside her homework—she's an A student—and go hang out with friends.) Her most common execution mistake, her coaches say, is that she goes out too hard. Katelyn's usual explanation: "I was excited."

RACING SPORTS are fundamentally different from game sports, which mix fun with pain. Running is pure agony until you cross the line. "Your sport is other sports' punishment," Denise likes to remind Katelyn and her brothers, Ryan (10) and Patrick (18), who will compete for Fordham as a distance runner next year. Katelyn tried soccer, volleyball and lacrosse when she was younger, but preferred the individuality of running. "You're able to set a personal goal and achieve it," she says. "In a team sport, you can't control the outcome."

Katelyn loves the way running burns off that extra energy. While she'll occasionally don headphones in the gym—"I feel like everyone else is listening to music, so I'm like, Oh, I don't want to look like the weird person not listening to it," Katelyn says—she would rather turn her brain off when training. That way she can spend a few hours focusing on only her watch and her body.

Her form is what Diglio first noticed when Katelyn tagged along to one of Patrick's workouts as a fifth-grader. Katelyn is only 5'4", but she drives her legs into the ground with such force—placing each foot directly beneath her center of gravity—that she nearly kicks herself in the backside on every step, giving her the stride length of someone much taller. She wastes almost no energy with side-to-side movement. It all goes into propelling herself forward.

There comes a point in each run, as the lactic acid spreads through her muscles, when she must decide whether to push through or let up. Katelyn embraces the pain. Her willingness to accept it sets her apart. "Some people want to be the best, but they won't put in the work," she says. "I actually put in the work that it takes to be the best."

Katelyn's coaches try to keep perspective. She is still a child. Her favorite vacation is a trip to Disney World. Her chief source of tension with her mother comes when she forgets to put the milk away. She is still new enough to the sport that she often doesn't know about the records she is chasing until after she breaks them.

Still, Katelyn's performances continue to astonish her coaches. "I feel a responsibility to the sport," Murphy says. "Talents like this don't come along all the time, and I really want to make sure I get it right—for her sake, her parents' sake and for running's sake."

FAME FITS Katelyn less comfortably than her singlet. She slides headphones over her ears after races—usually without music—so she can complete her cooldown without much interruption. She began running because it was fun and kept doing it because she was good at it; she seems politely bewildered that anyone else cares what she is doing. Strangers ask for photos at the gym or at meets and honk when they drive by her, and she tries to acknowledge them all, although she was taken aback by the Instagram direct message someone sent offering to fly her to his prom in Arizona. "I hope it was just a joke," Katelyn says, laughing. "I didn't answer."

Her parents restrict her media exposure, in an attempt to keep life as normal as possible. That task would be easier if Katelyn were just a little less exceptional. She has learned to trust the pace her coaches set, even when she wishes she were going faster. The idea is to go fast for a long time, after all. Next year she will enter a few races against pro runners, so she can "run and lose," in preparation for the next level, says Diglio. "When you don't lose you don't know how."

Katelyn barely catches her breath after most races before lamenting that she could have run faster, but Murphy points to one moment this spring when she seemed to realize what she had done. She had been talking about breaking 4:15 for the 1,500 meters all year. At the New York State Public High School Athletic Association championships in Cicero, N.Y., on June 8, she set a national record for her age in the 3,000 meters. Eighteen hours later Katelyn ran the 1,500 in 4:14.75, more than 13 seconds ahead of second place. By the time Murphy got to her, her grin could have lit up the scoreboard. "It was like, You just had a reaction that we all have when you do this stuff!" Murphy says.

Her short-term goals change constantly because she keeps exceeding them—after her 4:14.75, Murphy withdrew her from the next week's two-mile race and entered her instead in the mile, where she ran that 4:33.87—but the long-term ones remain intact: college, a professional contract, the Olympics.

But first she has a driver's test to study for and SAT prep books to read and milk cartons to put away. Back at North Rockland, Katelyn is pretending to run down the track as the shutter clicks. When the photo shoot finishes, she lopes across the scorching bleachers. "Mom, can we go?" she says. "I want to get to the gym before captains' practice."