Jump, Spin, Glide: The Science Of Figure Skating

IRA FLATOW: Hi, it’s Ira Flatow, and you’re listening to Science Friday. Today on the podcast, we’re in training for the final events in figure skating at the Olympics. When I watched the athletes spin, and jump, and glide while balancing on a razor-thin skate blade, I wonder how some of these seem to defy the laws of physics. And they test the limits of what the human body can do, don’t they? Especially the quadruple axel and the backflip performed by Ilia Malinin.

Well, here to guide us through the biomechanics of the fantastic feats on ice is Dr. Deborah King. She’s a professor of exercise science and athletic training at Ithaca College in Ithaca, New York. Welcome back to Science Friday.

DEBORAH KING: Thank you. Ira happy to be here.

IRA FLATOW: Nice to have you. Let me just ask, do you skate yourself?

DEBORAH KING: I am not a figure skater, no. I grew up just skating around outdoor rinks or ponds, but it was never a sport I participated in.

IRA FLATOW: Me neither. I did a couple of times on ice, but I don’t even want to talk about what the results were.

[LAUGHTER]

So to non-skaters, I mean, don’t they make all these difficult jumps seem so effortless? I have a difficult time telling the hard elements from the easy elements, so that’s why you’re here. What’s the hardest skill for a figure skater to do physically?

DEBORAH KING: Today, in men’s figure skating specifically, the hardest technical skill that’s being done is the quadruple axel, which is only being done in competition by Ilia Malinin.

IRA FLATOW: Describe what that is.

DEBORAH KING: OK, so the quadruple axel is a jump that is unique in that as an axel jump, the skater steps forward and is facing forward when they jump into the air. And people might not have noticed this when they’re watching the Olympics, but if you pay a little attention to the landings, you’ll notice they’re always landing their jumps backwards. So that means if you’re jumping off forward and doing a quadruple jump, there’s actually an extra half revolution you have to complete so that you’re facing backwards. So it’s a 4 and 1/2-revolution jump compared to the other quadruple jumps, which in and of themselves are very difficult but require four revolutions because they take off backwards. You do four revolutions and land backwards.

IRA FLATOW: Now I would think you have to be up in the air long enough, and you have to be able to spin fast enough.

DEBORAH KING: You’re absolutely right. In the quadruple axel, you’re probably seeing air times, 0.8, 0.9 seconds. They’re usually in the air only about– just a little under a second. When you watch the jump, it looks like it takes a little longer because you’re watching the approach, and you watch the glide out of the landing, but just the airtime itself is just under a second. But if you’re doing 4 and 1/2 revolutions in a second, that is spinning amazingly fast.

IRA FLATOW: I know if my head was spinning that quickly, I couldn’t balance myself or know where the heck I was. But you have to be able to do that, right?

DEBORAH KING: Right, your body awareness in the air so you know what revolution you’re at. And I don’t know if anybody, of your listeners, have noticed this while they’re watching skating, that you don’t see skaters spot. Like if you were watching ballet or something and doing turns, the head spots while they’re doing rotations. But if you’re doing 4 and 1/2 revolutions in a second, you’re not going to be able to spot and turn your head. So having your body awareness to be able to know where you are in the air and land is obviously amazingly difficult.

IRA FLATOW: Wow. And so why is it that he’s able to do this? Does he have a special talent, or is it practice or what?

DEBORAH KING: I think it’s going to be all of the above. One thing if you watch him jump that I think is amazingly impressive about his jumps is how high he goes. So he gets off the ground really quickly. He has a lot of power and just goes really high.

But while he’s doing that, if you watch his body position, it seems like he has almost immediately gotten into a really straight, tight-body position. So his legs are straight underneath him. They’re pressed really tight together. His arms come in really tightly across his chest, so he’s going high but snapping into his rotating position so quickly. So there’s not a moment wasted while in the air where he’s not able to rotate really fast.

IRA FLATOW: One of the problems he said he had during his failed attempts was that his head wasn’t on straight, so to speak. I guess the mental side of this is major.

DEBORAH KING: Oh, absolutely. The pressure to perform– and he’s been world champion and winning so many competitions and programs over the last almost four years, and the Olympics only come around once every four years. So that’s a pretty heavy expectation that everyone has for you. But those are really difficult skills to do. And no one’s going to land them perfectly all the time. And unfortunately, you’ve got to put the physical performance together and the mental performance together all at the right moment.

IRA FLATOW: Yeah, so I guess all the elements vary from one skater to another. I mean, does body size matter?

DEBORAH KING: Oh, body size is a hugely important factor in figure skating jumps. There’s a quantity in physics that we call the moment of inertia. And it really is a measure of an object’s resistance to angular acceleration. So when he goes in the air, he wants to have a little resistance to angular acceleration so he can rotate really fast.

And objects that can rotate really fast with small moments of inertia are really narrow. So you don’t want your body parts sticking out. You don’t want wide shoulders. You don’t want wide hips. So people who can be really long and narrow, almost like a pencil in the air, have an actual smaller moment of inertia, and that will allow them to rotate faster than someone who doesn’t have a small moment of inertia. So that’s one way body shape can make a difference.

IRA FLATOW: So that’s why you spin faster when you pull your arms in?

DEBORAH KING: Absolutely. Anybody who’s ever gone to the playground and played on the tire swing or on the merry-go-round and you can make it go faster by pulling your arms in, that’s the concept right there. But you also might notice when you try to pull your arms and legs in on the tire swing, it feels like they want to pull away from you.

IRA FLATOW: Right.

DEBORAH KING: So you have to be really strong to hold them in so that you can keep rotating fast and you don’t slow down in the middle of the jump.

IRA FLATOW: So how much of a performance is dictated by the physics? You mentioned this a bit. If you position your arm or your leg in a specific way at a specific time, if you don’t do that, you’re going to affect your performance because of the physics involved.

DEBORAH KING: Absolutely correct. So I think every skater is constrained by the laws of physics and needs to utilize their technique to be sure that they can optimize their performance within the laws of physics, not that they cognitively need to think about the laws of physics while they’re jumping, but the techniques that they use will allow them to work within those constraints of the time that you have in the air and your rotation speed. You need to be balanced out so you don’t under- or over-rotate the jump, for example if we’re just talking about completing 4 and 1/2 revolutions.

IRA FLATOW: Well, let’s talk about the laws of physics and the backwards flip. That was just mind-boggling. Is it a really hard thing to do, or is just something that your average good skater can do?

DEBORAH KING: That’s a really good question. If you think about it from a physics standpoint, you need to get enough, I guess, I would call it flip momentum, that you can get all the way over so that you get your feet back underneath you, because you don’t want to come up short. Because if you come up short, you’re going to land on your knees or your face, which would not be good. And you don’t want too much flip momentum that you over-rotate and then end up falling on your back.

IRA FLATOW: Yeah, yeah. I hate it when that happens.

DEBORAH KING: [LAUGHS]

IRA FLATOW: I’m sure the skaters do, too. One thing that always stuns me is how they can go from spinning really fast to standing still or from a spin to moving in a straight line. I mean, how do they shed all that momentum without seeming to slow down?

DEBORAH KING: I think there’s two different concepts that are being used to slow down their momentum. So one is that moment of inertia that we talked about. Generally, they’re spinning really fast. And then, all of a sudden, you see them open their arms up, so they’re extended out from their body. And so that’s going to slow you down a lot.

And the other thing that is probably harder to visualize when you’re watching them would be any torque being created from their skating against the ice. So skaters use the way they glide into a jump and the way they move their body on their blade to generate torque as they’re skating. When you see skaters skate, they skate on curves, so they’re coming in on a curve as they go into a jump. They come in and curve as they go out of a jump. So they have angular momentum as they come in, and they still have some angular momentum as they come out. So it’s hard to see that they’re generating angular momentum.

The same would be true in a spin, which you were talking about, that they come in and they’re on a curve, so that’s generating angular momentum. And then, they just snap their arms and legs, and they go really fast. And then, they can open up, and they’ll slow down. But they can also, when they stop, put the toe pick of their other foot in the ice, for example, and that will help create a force that will stop their angular momentum.

IRA FLATOW: Right. Well, speaking of forces, is it possible to measure the forces that are on the skater’s feet in their ankles and compare it to something non-skaters might understand?

DEBORAH KING: Yes, sort of. We don’t have a lot of really good equipment that naturally goes with a figure skate to measure the forces on the ice. There are a bunch of researchers working on it. But we have some really good estimates.

Some of the probably better estimates that either I’ve tried to look at or other people have looked at are for jumps that are probably as high as Ilia’s quad axle are. He could be having forces up 8 to 10 times his body weight when he comes down. A lot depends on your landing style or technique. You can land very stiffly and have a higher force or land absorbing force through your ankle, knee, and hip and have a slightly lower force, so we probably need to give a range because it hasn’t necessarily been measured directly for him. So 8 to 10 times your body weight. Gosh.

IRA FLATOW: 8 to 10 G’s?

DEBORAH KING: Exactly, yeah. That high force is only for several milliseconds, so it’s not like a fighter pilot or race car driver going around a corner for a long period of time. That would be pretty much hard to withstand by the human body. But you’re talking like 100th or 200th of a second you get this big-impulse shockwave up your leg that’s going to be close for a jump that high, 8 to 10.

IRA FLATOW: Wow, without breaking any bones or pulling any muscles.

DEBORAH KING: Ideally, yes. [LAUGHS]

IRA FLATOW: [CHUCKLES] I’m trying to compare it to a ballet, a ballerina or somebody who’s on their toes like that. I guess they’re not jumping that quite that high and coming down that fast.

DEBORAH KING: I think a ballet dancer probably jumps that high. I don’t 100% know, but I would think they could come close to that height. I think a difference in a ballet dancer in the landing versus a figure skate is, for at least most ballet that I’ve watched, when they land, they land on the ball of their foot, and they go through a bigger range of motion. So they lower themselves through the ankle, knee, and hip more gradually towards the ground so it’s less abrupt, so it won’t take quite as much force to act on the body during the landing to stop the person’s downward momentum.

You can think of it a lot like a safer barrier in NASCAR or the shock absorption in a football helmet that if you have something that can absorb forces and deform when you land, in this case like a ballet dancer’s ankle, knee, and hip can go through a range of motion, and spread the impact over a longer time period so the forces can be lower. In skating, that’s a little more challenging to do, but you do see skaters who have more of a deep knee bend and more of a hip flexion when they land, and sometimes they come down a little more stiff. And so that’s why maybe some of what you might see is probably closer to 6 times body weight, and sometimes they come down really stiff, and it might be closer to 10 times body weight.

IRA FLATOW: So you think some of these skaters might perform well in the other acrobatic events, the halfpipe, snowboard, freestyle skiing?

DEBORAH KING: Oh, that’s a great question. So I think what is unique to skating is that they mostly do twisting, except for, like you said, the backflip that we saw from Ilia.

Another sport that does a lot of twisting in the Winter Olympics is aerials. But when you see the halfpipe, they’re doing a lot of twisting, but they’re also doing a lot of flipping and inverts at the same time.

So I think it might depend on the sport, which one it would be easier for them to transfer their rotational skills to. I would think aerial skiing, even though you would not have long skis, at least the twisting. They are inverting in aerial skiing because they come off the ramp, and they are flipping while they’re going, but the motion they pick up is really a twist motion, which is much more like skating.

IRA FLATOW: Yeah, there are a lot of skating events at the Olympics. How different is this skating from a different kind of skating, like speed skating or other kinds of skating? Is it a whole different thing?

DEBORAH KING: I’m going to go and say a whole different thing. Not that a skater who figure skates– they know how to skate, so could they put on a pair of speed skates and go around? Probably, but even the equipment is very different, particularly if you look– well, look at all of them in short track, speed skating, the boot comes up over the ankle. But the blades, if you look down from the top, the blades are offset from the middle so that they can lean going around the corners.

And if you look at a speed skate that’s for the long track, when you look at their boots, the boots usually are not coming up over the ankle, and they have a hinge on the front. So when you push off, you can have a more smooth transition of force all the way through the stroke. So I think people could probably put them on and skate, not immediately fall over like I might, but–

[LAUGHTER]

IRA FLATOW: My ankles aren’t even strong enough–

[INTERPOSING VOICES]

DEBORAH KING: –transfer their skills from one to the other.

[LAUGHTER]

IRA FLATOW: I get it. The free program, that’s only about– well, “only–” it’s only about four minutes long. That’s pretty long for me if I were skating.

DEBORAH KING: Right.

IRA FLATOW: But there’s so much athleticism packed in. So I’m saying and thinking that endurance, cardio must be a very big component here.

DEBORAH KING: Yeah, the free skate, so you’re absolutely right, four minutes. That’s an extremely difficult length of time to train for. That’s like a miler in track and field. So it’s a combination of both aerobic power where you’re using oxygen and then your anaerobic energy systems.

And so that’s a particularly difficult time to train for because it’s not predominantly aerobic, and it’s not predominantly anaerobic. So it involves training both systems. And you need to, obviously, get through the four minutes, but you need to get through the four minutes while you’re doing jumps, but then transitioning to gliding beautifully across the ice and then doing something with a very immediate need for power, like another jump and balancing on one leg. So it’s challenging your energy systems while you also have to present yourself beautifully doing really difficult skills that are fast but also skills that are slow and under the control of your body, if that makes sense.

IRA FLATOW: It does make sense. My last question for you, and it’s a question about questions. I mean, what are the big questions in figure skating physics? What are sports scientists interested in learning?

DEBORAH KING: So I think one thing is really quantifying the loads with landing and seeing how the loads are related to the difficulty of the skill, for example. Are the loads that we’re seeing from different skaters, do they relate to overuse injuries that we see in skaters, that we could have some really evidence-based advice on training and scheduling training to try to reduce injuries?

And another one would be thinking about off-ice training and how targeting different muscle groups and different abilities and aspects of skating. And off-ice training, is that really translating into techniques on ice that are either, one, helping with their performance and/or helping to reduce injuries.

IRA FLATOW: Do you have an Olympic weakness? I mean, a sport that you have to watch?

DEBORAH KING: I have more than one Olympic weakness. Cross-country skiing, absolutely have to watch. And the downhill.

IRA FLATOW: See, I’m more of a curling guy.

DEBORAH KING: Oh, my gosh. I love curling, too.

[LAUGHTER]

IRA FLATOW: It’s been great to have you back on the show.

DEBORAH KING: Well, thank you so much. It’s been a pleasure.

IRA FLATOW: Deborah King, professor of exercise science and athletic training at Ithaca College, of course, in Ithaca, New York. This episode was produced by Charles Bergquist. And honestly, we’d love you to rank our elements high for both technical merit and artistic impression. Rate and review us wherever you get your podcasts. I’m Ira Flatow. We’ll see you soon.

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