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In many of her biggest races, Katie Ledecky is leading before she even touches the water.

In the 800-meter freestyle final at the 2012 London Olympics, which produced her first Olympic gold medal; in six of her nine individual swims at the 2015 world championships, where she pulled off an unprecedented sweep of the 200 through 1,500 freestyles; in the 800 free final at the 2014 Pan Pacific Championships, a world record; and the finals of both the 400 and 800 free at the 2012 U.S. Olympic trials — in all of those races, and in many others, Ledecky was the first swimmer off the blocks, her "reaction time" (the interval between the starter's gun and the instant her feet leave the blocks) fastest in the field.

It is not a skill Ledecky, 19, needs or cares about. There isn't much benefit in beating opponents off the blocks by a couple hundredths of a second when you typically win your core events by several seconds, or even tens of seconds. And where fast starts are a part of her practice routine, it is only in the larger context of the first 15 meters as a whole.

But as a symbol of Ledecky's sheer athletic brilliance, her perfection of the first movement of a race is illustrative. Getting off the blocks fast requires some combination of hard work, athleticism, intense focus and perfectionism. And try as people might to find some simple explanation for Ledecky's dominance of swimming, the truth is more complex, and it lies somewhere in that recipe.

"This is a one-in-a-billion human being," said Washington Capitals and Wizards owner Ted Leonsis, a longtime friend and associate of Ledecky's family. "She has a very special family, and she's an incredibly gifted person — with a high, high self-actualization and self-awareness, otherworldly good instincts and intelligence, a gifted physiognomy, plus an incredible drive to be the best. And it's all natural."

As Ledecky prepares to launch herself into the U.S. Olympic trials in Omaha, Neb., with the 2016 Rio de Janeiro Olympics looming six weeks in the distance, she already may be the most dominant athlete in sports, as measured by the gap between her and everyone else in her discipline. At the 2015 worlds, against the best competition the globe could offer, she won the 1,500 freestyle by more than 14 seconds and the 800 free by more than 10. When she set the most recent of her 11 world records, in the 800 free at a meet in Austin in January, her margin of victory was 17.81 seconds.

Usain Bolt is occasionally beaten. Serena Williams doesn't win every Grand Slam. Stephen Curry goes 5 for 20 now and again. But Ledecky has swum in 12 individual finals at major international meets, and has never lost.

"She's the greatest athlete in the world today by far," said Michael J. Joyner, an anesthesiologist and researcher for the Mayo Clinic in Rochester, Minnesota, specializing in human performance and physiology. "She's dominating by the widest margin in international sport, winning by 1 or 2 percent. If [a runner] won the 10,000 meters by that wide a margin, they'd win by 100 meters. One or 2 percent in the Tour de France, over about 80 hours of racing, would be 30 or 40 minutes. It's just absolutely remarkable."

The people who coach her, train with her and race against her are quietly bracing for another monster summer from Ledecky, with the question not a matter of wins and losses but how much faster she can possibly go.

"If she never goes faster, she's already an all-time incredible performer," said David Marsh, head coach of the 2016 U.S. women's national team. "But the reality is, knowing she has her sights set on Omaha and Rio, I think we may see some great swims."

She is already considered the best female swimmer in the world at the moment, but with a representative showing in Rio — where she has a legitimate shot at five medals, including four golds, with perhaps a world record or two sprinkled in — she would, before the age of 20, enter the conversation of the best ever.