After the run, the roundoff, and the back handspring, Biles translates her forward motion into a leap into the air. But this isn’t a leap as you or I might attempt one. Biles’ feet and hands are almost completely straight. Even exiting her roundoff, Biles’ feet are well forward of her stomach, not beneath or behind her body as you might expect if she were simply pushing off. “She basically ricochets off the spring floor. She doesn’t bend and jump,” Sands says. “It’s perfect physiology, because the elastic nature of muscles means she’s going to get back an enormous amount of force for a relatively small investment.”

All this happens fast. Typical takeoffs in gymnastics last less than a tenth of a second. Biles, in other words, has learned to bounce—hard. Even for maneuvers less airborne than Biles’—like, say, two backward somersaults in rapid succession—forces can reach 17 times the gymnast’s body weight, and Biles is pulling even more force here. “If she had to jump nine feet in the air? Give me a break. Even on the spring floor, she wouldn’t get there,” Sands says. But Biles’ fast-twitch muscle fibers work harder. “She gets there by very skillfully maximizing the elastic and contractile motion of her muscles in a very efficient fashion.”

OK, so, Biles is go for liftoff. On the floor as on the beam, she then makes another subtle adjustment. She doesn’t take off evenly. In the floor routine she starts in a “puck” position—part pike, a bend at the hips, and part tuck, in which both hips and knees bend—and twists about an eighth of the way around. This is Biles initiating her twists and somersaults before she ever leaves the ground. “She does the twist from the supporting surface so she doesn’t need to rely on twisting in the air,” Sands says.

Twisting in the air’s possible, yes, but it takes a different set of skills. A so-called cat-twist rotates one part of the body in the opposite direction of another. Pretend, as the physicist Cliff Frohlich proposed, that a body is basically just two cylinders joined at the ends, like unattached sausage links. Give one a twist in one direction and the whole assembly will flop around. It’s also how astronauts move in zero-g.

That ain’t how Biles is moving. It also helps that Biles is relatively small and tremendously strong; smaller people flip faster when they tuck because, in physics terms, they have a smaller moment of inertia. That’s why Biles starts her flight with arms wide, then brings them in while straightening out her body. By shifting her angle slightly, Biles primes her body for twists and flips in the air—and because she’s moving so fast, and bouncing so high, she has time for lots of both.

Her arc and rotation—longitudinal and transverse—aren’t completely ballistic, though. Freeze-framing through Biles’ routine, Sands points to one small midair adjustment that shows how skillful her landing was. Near the end of her second somersault, Biles opens her tuck a little. She’s facing the mat, and, as far as Sands can tell, Biles realizes that she’s a tiny bit under-twisted. But she’s high enough to be able to do something about it.

“She extends her right arm in a small circle,” Sands says. “She moves her arm backward, and that helps her align her trunk and her legs so she can finish her turn.” It’s called a secondary-axis turn, a movement of part of the body outside the direction of angular momentum that siphons some of that motion off into a different direction.