Getting High: Physics Of The Fosbury Flop

The world record for high jump — the event in which a person hurdles himself over a horizontal bar — is just over 8 feet. That's like leaping over a stop sign, and clearing it by a foot. Jesus Dapena, of Indiana University, has studied the high jump for 30 years, filming athletes to understand exactly how they produce the force required to clear the bar.

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IRA FLATOW, HOST:

Flora Lichtman is here with our video pick of the week, and she has Olympic fever, too. I can see her brow sweating.

(LAUGHTER)

FLORA LICHTMAN, BYLINE: Right. All right. The tour continues for the Olympics. The video pick of the week this week is about how humans reach great heights, and I don't mean that in the feel-good way. Who wants that?

FLATOW: Uh-huh.

LICHTMAN: No. I mean it literally - the high jump, which I became fascinated with this week. Did you know that the world record for the high jump is just over eight feet?

FLATOW: Wow.

LICHTMAN: Propelling yourself over - I can't even reach eight feet.

(LAUGHTER)

FLATOW: It's a long way from Valeriy Brumel, whom you never heard of.

(LAUGHTER)

LICHTMAN: Anyway...

FLATOW: That is really - how you get your body off the ground eight feet.

LICHTMAN: Over a bar, a whole bar.

FLATOW: You know, that's just going over a UPS truck, right?

(LAUGHTER)

LICHTMAN: Yeah. We went around the city to look at some things that are eight-feet tall -the walk sign, the street light, the UPS truck, eight feet. It's certainly incredible. So I couldn't really understand...

FLATOW: Right.

LICHTMAN: ...how this worked. But fortunately, other people do, like Jesus Dapena who studies biomechanics at Indiana University. And we called him up for the video pick of the week. And he's actually here with us today to walk us through the science of the high jump. Welcome to the program, Dr. Dapena.

DR. JESUS DAPENA: Thank you very much. Thank you for having me.

LICHTMAN: OK. So what are the key ingredients for a successful high jump? Basically, how do you get that high?

DAPENA: OK. The first ingredient is your body. You need to - it's genetics plus training. So you need to choose your parents very carefully, and then you have to work very hard to get your body to have very good muscles and be very flexible and good coordination and all that. That's by far the main things that will get you to be a good high jumper. But there's another thing which is your technique. If you know how to high jump, you're going to jump a lot higher than if you don't know how to high jump.

The main factor is still the body, but the technique also plays an important role. So what you want to do is during the takeoff - you have a run-up and a takeoff, and then you're in the air. And during this takeoff phase, which lasts like between 0.16 and 0.20 seconds, you need to make on the ground a big vertical impulse. So you need to push on the ground down very hard and for a relatively long period of time. And how do you get to push really hard on the ground?

Well, there's various ways to do that. One of them is, well, you actually - well, you make a big effort and you just try to push really hard on the ground. But there's other things that you do to help you make a better impulse. One of them is you want to have a fast run-up. By having a fast run-up, by the time that you plant your foot to do the takeoff phase, you will not put your foot directly below your body. You'll put it below your body, of course, but also ahead of your body.

And by doing that, because of this momentum you have forward from the run-up, you'll put your foot ahead of your body and this will tend to - and you have your leg fairly firm so that this will tend to flex your leg, and you'll be fighting against that flexion of the takeoff leg. And in those conditions, your muscles can make really big forces, so that allows you to make a big downward force on the ground.

LICHTMAN: OK. Let me interrupt you for a second and just remind people that they're listening to SCIENCE FRIDAY on NPR. I'm Flora Lichtman talking with Dr. Dapena about the high jump. OK. So you have your foot in front of you, and that sort of stops the forward momentum of your body?

DAPENA: Yeah. It doesn't quite stop it completely, but it reduces your forward momentum. And at the same time, you're producing a lot of upward momentum because of the vertical downward force that you make with your foot against the ground.

LICHTMAN: What about the rest of your limbs, do they play any kind of role, or is it just that leg?

DAPENA: Yes. The takeoff leg is the most important part of the body for high jumping, really, but, you know, you do need the rest of the body. During the takeoff phase, if you swing your arms upward really hard and if you swing your lead leg, that is the - your nontakeoff leg, if you swing them both up, what you're doing is you're making upward forces on those limbs. And by reaction, then those limbs make downward forces on your trunk, and they squeeze your whole body harder against the ground, so you get to make a bigger force against the ground that way, too.

LICHTMAN: Mm-hmm. So that action and reaction. You throw the arms up, and they push down, and that compresses that jump-off leg, like...

DAPENA: That's right.

LICHTMAN: OK. And is there anything else, or is that - are those the key things?

DAPENA: Yes, yes. The third element that you need is - you need to be in a relatively low position at the start of the takeoff phase. I mean, it can't be extremely low, but you have to be moderately low. And the reason is that you want a big vertical impulse, which means you need a big force over a relatively long time, so the product, the force and time, is what counts. So a fast run-up gives you a big force. Swinging the limbs very actively also gives you a big force. And the extra time you get by being in a low position at the plant and a high position at the end of the takeoff, that gives you more time to push on the ground, which is difficult to do because it means if you're going to be low at the start of the takeoff phase, it means you got to be low in the last steps of the run-up. So I'm asking you to run really fast and to run with the hips in a very low position, which is not really all that comfortable, but you still have to do it.

LICHTMAN: That's like the Groucho Marx.

FLATOW: And it's our video pick of the week this week on our website. If you go to our website, Flora's put together this great video that shows you how to do the Fosbury flip.

LICHTMAN: Flop.

FLATOW: Flop.

(LAUGHTER)

FLATOW: Backwards, on your back, 8 feet up, over the bar.

LICHTMAN: Yeah.

FLATOW: It seems impossible, but you've done a great video on that.

LICHTMAN: Yeah. It's worth - these are - this is mostly footage collected by Dr. Dapena. In fact, you know, you've looked at this over the years, and I guess we'll talk about that more a little bit later in the program after the break. But if you go to the website, check it out because you can actually see, deconstructed, the entire jump. It's really, really neat.

FLATOW: Is there something you don't know, quickly before that, Doctor, that, you know, you'd like to know more about?

DAPENA: Are you asking me?

FLATOW: We've run out of time.

DAPENA: Oh.

FLATOW: We're going to keep you. We have to go to the break, so we'll get the answer after the break. But we've ran out of time until the break, so stay with us. We'll be right back after this break. I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

(SOUNDBITE OF MUSIC)

FLATOW: This is SCIENCE FRIDAY. I'm Ira Flatow. We're doing our pre-Olympic extravaganza this week. Flora Lichtman is here with me. We started off talking about some of the high technology involved in the Olympics. We moved on to doping, you know, and chemical and drugs. And, in fact, on our website at sciencefriday.com, we have a quiz. If you think you know about doping in the Olympics or doping in sports, take this quiz on our website at sciencefriday.com.

And that - now with us is Jesus Dapena, who is a high jump expert and professor in the department of kinesiology at Indiana University. With me is Flora Lichtman who's done a great video and talked to him about it.

LICHTMAN: Yeah. We're talking about the high jump. And I - maybe you can describe for people who aren't high jump junkies like me what the Fosbury Flop looks like.

DAPENA: Well, the Fosbury Flop, you have the bar and you start your run up. You have a run up, a take off and an airborne phase. And then the run up is you start going perpendicular to the bar, then you curve the run in the last four, five steps, then you plant your take-off leg on the ground and you make a big impulse on the ground, and you receive an upward force from the ground, upward impulse, and then you go up high and you go over the bar if you're lucky.

So the Fosbury Flop, specifically, its main known characteristic is that over the bar, you go on your back because you take off from the ground and your body is pretty much vertical, and you're facing more or less along bar, and then you're going to be twisting about 90 degrees, so your back is pointing towards the bar. And also, you're going to be doing a partial somersault so that your shoulders go down, your legs go up so the peak of the jump, you're on your back and horizontal and perpendicular to the bar.

LICHTMAN: So belly up and backwards.

DAPENA: Right.

LICHTMAN: And how did this technique come about?

DAPENA: Well, an athlete called Dick Fosbury, he was - when he was in high school, last years of high school or maybe when he was a freshman in college, he was trying to do the normal technique, which was called at the time the straddle. And he just couldn't get to do it right. So he used a technique called the scissors, which is a very old, primitive and very inefficient technique, but he was playing with that technique. And at some point, when you - OK, in the scissors, you come at an angle to the bar. You'd take off, and let's say you're taking off from the left foot. If you'll take off from the left foot, the right foot goes over the bar, and then your right leg goes over the bar and below, and then the left leg goes up. So it's one leg goes up and then the other leg goes up so you - and you're over the bar.

Well, when the bar goes up really high, it becomes very difficult to get the first leg over the bar. So what Fosbury did - well, not unconsciously but subconsciously, he didn't get the leg over the bar. So probably, the first time he did it, he knocked off the bar with both legs. But then, over time, he also accidentally began twisting his body so that instead of being facing along the bar or towards the pit, he was facing away from the bar. And that way, his head went into the pit first. And by doing that, it worked very well for him.

LICHTMAN: And he ended up winning the Olympics that year, in 1968, right?

DAPENA: That's right. He - I'm not very sure exactly when he came up with this technique, but it may have been - OK, '68 is when he won the Olympics. '67, he won NCAAs. And maybe, I don't know, '64, something like that, and soon he was beginning to play with this.

LICHTMAN: So now everybody does the flop. Is it somehow biomechanically better than the straddle, which was the one that preceded it?

DAPENA: Most people you'll talk to will say that, yes, it is better, but I don't believe so. What I believe is that there are different athletes with different body types. And for some of them, the Fosbury Flop is, indeed, the best way to go about it. But for others, the straddle would be the best way to go about it.

LICHTMAN: So just a cultural thing that people are doing the flop versus the straddle?

DAPENA: It's cultural and, in part is, it's practical because the Fosbury Flop is a much easier technique to learn. A technique that'll take you maybe two years to have a certain level of quality in your technique, in the straddle, to get the same - comparatively the same quality of technique in the flop in maybe six weeks or a month.

LICHTMAN: Thank you, Dr. Dapena, for explaining this to us. I can't wait to watch the Olympics and look out for all of those lead ups to the jumps.

DAPENA: OK. I'll be doing the same thing.

(LAUGHTER)

LICHTMAN: Jesus Dapena is a professor in the department of kinesiology at Indiana University.

FLATOW: OK. Thank you, Flora. And it's our video pick of the week up there on our website.

LICHTMAN: Go check it out.

FLATOW: We put the whole thing together. And if you want to see how the Fosbury Flop is done, it's up there.

LICHTMAN: A very academic look at the flop. It's very cool.

FLATOW: You know, it's there because I can't do it.

(LAUGHTER)

FLATOW: You can't (unintelligible).

LICHTMAN: Oh, not even close.

FLATOW: Oh, OK. Thank you. Thank you, Flora.

LICHTMAN: Thanks.

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