In 1991, Tonya Harding made history when she became the first American woman to perform a triple axel in competition.
Triple axels require 3 and a half rotations in mid-air, and they are notoriously difficult. Mirai Nagasu, who recently pulled one off at the 2018 winter Olympics, is only the third American woman to perform a triple axel in competition and the first to have ever done so at the Olympics.
In a new video, Vox explores why the triple axel is such a big deal, using biology and physics to explain.
To get some expertise, Vox sat down with Deborah King, who has studied the biomechanics of single, double and triple axels in figure skating.
"They need to generate the vertical velocity, but they also need to generate their angular momentum, or their rotational momentum for the jump, and that's all gotta happen during the approach up to the takeoff," she explained to Vox.
Unlike other jumps that require skaters to push off the toe, a triple axel requires that skaters push off the outer edge of their skates. The forward momentum gives them more air. And, the more time you have in the air, the more time you have to spin. In other words, higher jumps are better.
To complete a triple axel once in the air, a skater needs to spin - and fast. Some of that spin comes from the push off, but most of it comes from the skater's own body once they are airborne.
Strangely enough, when you look at the data, the triple axel jump length is actually shorter than the double axel jump. But it actually makes sense, because all of that extra energy is going into rotation instead of distance. So, for instance, when Tonya Harding leapt into the air way back in 1991, she had to pull her body into a spin as quickly as possible.
Biomechanics aside, the triple axel is at its heart a physics problem.
"In terms of body position, you don't want your elbows sticking out, you don't want your arms right out in front of you, you don't want your knees sticking out, you should look as close as you can to a pencil," said King.
But landing a jump after 3 and a half spins, with such high speed of rotation, is no easy matter. To land on the ball of the opposite foot, skaters have to compensate for a huge rotational velocity, all while trying to look good.
The more physics you learn about the triple axel, the more impressive it gets.