On Sunday night, two gymnasts literally put their lives on the line to try to beat Simone Biles in the women’s vault finals of the Rio de Janerio Olympics.

Oksana Chusovitina of Uzbekistan and India’s Dipa Karmakar both attempted to pull off the “Vault of Death,” which consists of hurling oneself into the air, flipping into two-and-a-half somersaults, and landing on your feet. Casual.

The move is so difficult that attempting it can increase the judge’s base scores, but failure could literally mean death.

Both women had a lot on the line, but they also — fittingly — had established themselves as badass women who had to overcome a lot of obstacles for the chance to do the Produnova. At 41, Chusovitina was the oldest athlete ever to compete in women’s gymnastics. Karmakar was the first Indian to make a gymnastics final and had trained in a ramshackle gym without much funding. Besides Chusovitina and Karmakar, only five gymnasts had ever successfully pulled off the move.

The namesake of the Produnova was Yelena Produnova, a Russian who debuted the technique in 1999. It never got her the gold, but it sure got her a ton of attention — one wrong move and the gymnast’s neck can crack, her head can split open, and she can become paralyzed.

Here’s the original Produnova sticking it:

In other words, it takes guts to do the Produnova. When the New Yorker asked gold-medal Olympian Simone Biles why she doesn’t try the Produnova, she replied, “I’m not trying to die.”

But neither Chusovitina nor Karmakar were able to quite nail the move. Chusovitina’s landing was decidedly more dangerous, but she tumbled rather gracefully back up.

RIO DE JANEIRO, BRAZIL - AUGUST 14:  Oksana Chusovitina of Uzbekistan falls while competing in the Women's Vault Final on Day 9 of the Rio 2016 Olympic Games at the Rio Olympic Arena on August 14, 2016 in Rio de Janeiro, Brazil.  (Photo by Patrick Smith/Getty Images)
RIO DE JANEIRO, BRAZIL - AUGUST 14: Oksana Chusovitina of Uzbekistan falls while competing in the Women's Vault Final on Day 9 of the Rio 2016 Olympic Games at the Rio Olympic Arena on August 14, 2016 in Rio de Janeiro, Brazil. (Photo by Patrick Smith/Getty Images)

Karmakar, whose coach called the move a “risk that we have to take”, landed on both her feet, but had a little scoot in the end that might have cost her the bronze.

Perhaps the greatest challenge of the Produnova is getting enough height. As Lauren Hopkins of SB Nation notes, a gymnast only has about two seconds to rotate her body two times after her hands leave the vault. Without the right height and rotational speed, the gymnast won’t get enough time to rotate fully — which could lead to a disastrous landing.

Getting the right height is an exercise in physics reliant on strength. Gymnasts have to reach a maximum velocity on their approach to the springboard to get maximum force — the more mass and acceleration used, the more air they are going to get. That’s in line with Newton’s second law while his third law (for every action, there is an equal but opposite reaction) explains why the exertion of force on the springboard is what enables the athlete to propel into the air. More air time affects the rotational velocity of the gymnast and — in the case of the Produnova — hit the two-and-a-half somersaults on their way down.

There’s also the factor of kinetic energy — the kinetic energy is transferred to potential energy when the gymnast hits the springboard. When gymnasts “pop” off the vault — using their shoulders to gain maximum spring — they increase the potential energy that will help them have a successful landing. The problem with the Produnova is that most women simply don’t have enough upper body strength to get to that point.

Meanwhile, physicists are still amazed by the “The Biles” — Simone Biles’ signature move that has her flipping twice with her body fully extending, paired with a half-twist landing. While the Produnova is a dangerous feat pulled off by a few, “The Biles” has only been completed by its namesake.

Photos via Getty Images / Patrick Smith, Getty Images / Alex Livesey

Sarah is a writer based in Brooklyn. She has previously written for The New Republic, Pacific Standard, and McSweeney's Internet Tendency. She likes cheese especially when paired with a full-bodied joke.