The 4′8″ human projectile tore down the runway, suddenly plunged forward to execute a back handspring, then propelled herself skyward off the vaulting table. Once around … twice… 2½ times, and bang!

Simone Biles landed on the bright-blue mat, becoming the first woman to complete a wild move called the Yurchenko double pike in competition.

The 24-year-old decorated gymnast nailed the historic vault in May, at the U.S. Classic competition in Indianapolis. She substituted a less difficult maneuver at June’s U.S. Olympic trials, but she is widely expected to go for the Yurchenko double pike once again at the Olympics this month, in Tokyo.

Experts in the biomechanics of sport say that few, if any, women could accomplish the same feat. Others may put in the same long hours in the gym as Biles does, but her combination of muscle and body type is unique. She runs nearly as fast as an elite runner, but must control her speed. And while all gymnasts need to be psychologically tough, she also digs deep to try increasingly risky skills.

For a breakdown of how Biles defies gravity, we spoke to Fred Turoff, a longtime Temple University gymnastics coach who studied physics in graduate school, and William A. Sands, a Salt Lake City-based physiologist who has worked with the U.S. gymnastics, skiing, and snowboard teams.

“The average person can’t understand how strong she is,” Turoff said. “She’s amazingly strong for her body size.”

“Gymnasts are tiny to begin with, but she’s tiny even for gymnastics,” Sands said. “Coupling it with a high level of strength and power makes her a double or triple threat as far as executing skills.”

Biles also is known for an eye-popping move in her floor routine called the triple double, along with many other skills. But at least two other women do a triple double. For now, the Yurchenko double pike belongs to Biles alone.

Here’s how she does it.

The run-up

For a gymnast to generate enough momentum to launch herself into an elite-level vault, success depends on foot speed.

“The speed from the run is of course essential,” Sands said. “That builds up the amount of momentum that you will later spend like a bank account on various aspects of the vault. The more you have in the bank account, the more you can spend.”

And by all appearances, Biles fills up her account as much as anyone.

Just how fast she runs is a bit of a mystery. In the video of Biles’ Yurchenko double pike in May, the skewed camera angles make it difficult to measure her top speed and other elements of the vault, Sands said. He’d love to get precise footage shot at a perfect right angle in order to see what makes Biles tick, but no dice.

“They almost never shoot the video in a fashion that allows analysis,” he said. “It’s a prettiness and a television thing.”

But Christoph Schärer, a sports scientist at the Swiss Federal Institute of Sport Magglingen, has used lasers to measure the runway speed of other elite gymnasts. After seeing footage of Biles, he estimated that she is easily in the top ranks, probably exceeding 18 mph by the time she nears the end of the 82-foot runway.

She almost certainly can go faster. The top female sprinters run more than 20 mph. But a gymnast’s goal is not to go all out. Biles has to channel that speed into a series of complex movements that require exquisite body discipline.

“It’s not just raw strength that you need, or raw power,” Sands said. “You need power or strength under control.”

Redirection

Next, Biles transfers her horizontal momentum into new directions. She pitches forward into a cartwheel-like move called a round-off, flipping once around until she returns to an upright position. From there, she drives her feet forcefully into the springboard, launching herself upward into a back handspring — using her hands to propel herself off the vaulting table.

It all happens in a fraction of a second, with so much going on that it’s hard for mere mortals to appreciate. But in its essence, what’s happening is straightforward, said Temple’s Turoff, who coached 1992 Olympian Dominick Minicucci.

“You take your horizontal momentum and energy, and you translate it into rotational momentum and energy,” he said. (And vertical. Upon flying off the table, Biles appears to reach a height of more than two body lengths in the air.)

This type of takeoff is what defines the Yurchenko family of vaults, named for former Soviet gymnast Natalia Yurchenko, now a coach in Chicago. The difference among the various versions comes with the types of twists and turns that the gymnast executes after hitting the table.

That is where Biles distinguishes herself among the women. No one else has done 2½ rotations, much less in the L-shaped “pike” position (though male gymnasts have done so).

Achieving that many rotations would be easier in a tight somersault. But Biles has chosen a more impressive route, extending her frame into the L so that it is harder to spin around.

The key is a physics concept called the moment of inertia — loosely speaking, a measure of how the mass of a rotating object is spread out along its length. Baseball players exploit this phenomenon when choking up on a bat — gripping it higher on the handle so that the bat is effectively shorter, allowing them to swing faster.

Biles is doing the opposite, extending herself into a longer L-shape, requiring herself to work even harder to whip around 2½ times.

Yet even so, at the U.S. Classic, she actually over-rotated, meaning that she had to stutter-step the landing to bring herself to a stop, Turoff said.

“She has power to spare,” he said.

It helps that she is short, with a high ratio of muscle to body size. Most female gymnasts decline in that regard with age, their strength not keeping pace with the physical changes of puberty. That can lead to injury, as some moves place loads on bones and ligaments that are equal to several times the athlete’s body weight.

Not so with Biles. Sands said she appears to have maintained plenty of muscle, enabling her to pull off her moves without the taping and braces that so many of her competitors use.

“Simone is an exception,” he said. “I would bet her individual tissues are strong and elastic.”

Among her many fans is the woman for whom the family of vaults is named. Natalia Yurchenko spoke about Biles’ double pike recently on the Olympic Channel, a broadcast operated by the International Olympic Committee.

“I was dreaming about seeing it,” she said. “It was kind of tears of joy because you create something and you wait for the future generation to use it. ... I don’t think it can be better. It was just so amazing. I was amazed that we have Simone Biles, who can raise us all to that kind of level.”

When the gymnastics events get underway on July 25 in Tokyo, Biles figures to amaze once again.