By Alex Abad-Santos From Vox CULTURE

American sprinter Allyson Felix would’ve had another Olympic gold medal instead of a silver if Shaunae Miller had stayed on her feet. Miller, a fantastic runner from the Bahamas, beat Felix in the women’s Olympic 400-meter sprint on Monday night by diving, belly-first, for the finish line.

Miller came out of the blocks with a big lead on Felix. But as she approached the finish line, she seemed to run out of gas, with Felix breathing down her neck in the last few meters. So Miller dived, her torso crossing the finish line at 49.44 seconds, seven-hundredths of a second before Felix’s 49.51.

The race ended with Felix on her feet and Miller on the ground looking spent. If Miller had stayed upright, she would have lost. If Felix had dived, she could have won instead. Miller’s dive was clearly a move of desperation.

And it’s completely legal.

Diving is legal in track and field, but it’s also risky

In the wake of Miller’s win, there was a lingering question from fans watching at home of how legal her move was. But it was completely legal. In fact, the rules of track and field state that you hit the finish line when your torso, which is considered different from your head or arms, crosses the finish line.

“The first athlete whose torso (as distinguished from the head, neck, arms, legs, hands or feet) reaches the vertical plane of the closest edge of the finish line is the winner,” NBC explains.

This is why runners lean forward in close races — to get their torsos over the threshold.

Miller’s dive allowed her torso to cross the finish line before Felix’s, even though it seemed like she had run out of gas. And Miller isn’t even the first track and field athlete at these Olympics who dived to get a better result.

In the preliminary heats for the 110-meter hurdles, Brazilian runner Joao Vitor de Oliveira dived across the finish line and finished fourth, earning a spot in the semifinals.

And here is American sprinter David Neville diving for the bronze medal in the 400-meter at the 2008 Olympics. He won the medal by .004 seconds:

The question that arises, then, is if diving worked for Miller, de Oliveira, and Neville, why don’t runners dive more? As Bill Nye pointed out during the 2014 World Series, sliding into first base — a cousin of the track and field dive — isn’t any faster than leaving your feet:
The goals are slightly different, but the physics are similar. In baseball, you’re reaching for the bag, while in a race, you’re looking to break that finish line plane with your torso. You’re essentially looking to win with a short burst of speed.

But as ESPN’s Sport Science feature explained, what matters is when you start the dive. The start of the dive is actually faster — for that split second — than running, but the moment your feet leave the ground on a dive, deceleration occurs. If a track and field runner dives at the wrong moment, it could easily mean losing.

Essentially, Miller, de Oliveira, and Neville all dived at the the right moment in the race. And they have the results to show for it.

IMAGES:

Shaunae Miller of the Bahamas (L) dives over the finish line to win the gold medal in the Women’s 400 m final ahead of silver medalist Allyson Felix of the United States (C) and bronze medalist Shericka Jackson of Jamaica (R) on Day 10 of the Rio 2016 Olympic Games at the Olympic Stadium on August 15, 2016, in Rio de Janeiro, Brazil. Alexander Hassenstein/Getty Images

David Neville diving in 2008

For more on this story and video go to: http://www.vox.com/2016/8/15/12495316/allyson-felix-shaunae-miller-400-meter-olympics-rio