What We Continue to Learn from Multi-Camera, High-Speed Videography in Biomechanics by Jan Prins, University of Hawaii (2013)


What We Continue to Learn from Multi-Camera, High-Speed Videography in Biomechanics

by Jan Prins, University of Hawaii


[introduction, by Steve Morsill]

My name is Steve Morsilli, I’m one of your ASCA board members.  I thank you for being here this afternoon.  I had the pleasure of introducing Dr. Prins last year also.  I was coaching with a buddy of mine way-back in the mid-1970s when I started to hear the name Jan Prins from Hawaii.  So Dr. Jan has been doing this an awful long time—I think I just dated both of us.  But he’s afraid he’s going to put you to sleep; if you’re in this room you are here to hear what he has to say.  I’m sure it’s going to be a great presentation.  Dr. Jan Prins.


[Prins begins]

Thank you.  Thank you, Steve.  I want to also thank John and the board for inviting me back; terrific to come back.  Most of the stuff I’m going to show you has video in it.  So some of that stuff I will clarify, if needed, at the end; so if you don’t mind, just hold-off on your questions till I’m done.


What we’re doing, this is again a continuation of about seven or eight years of working with these cameras, and in San Diego was the first time we talked about it.  And what we did at the beginning was just look at freestyle: the difference between straight arm, bent arm, dropped elbow, S-pull, all that stuff.  So today I’ve got some more fun stuff to show you, because in the last two years we’ve had some really-good swimmers visit us.  Two weeks after the Australian Olympic Trials last year; [James] Magnussen and a bunch of people got on a plane and came over; so I am going to show you some footage of him.  And then about a month ago, Matt Brown brought Emily Seebohm and his team.  So I’m going to show you some footage from them.  So that makes things a lot more interesting.


As you can see we use multiple high-speed cameras—and I’ll go into this.  Before I show you the videos of the reports, I’m going to show you just about a two-minute presentation on… (can we turn this light off here, this thing from the top.  I’m going to stop it right here.)  So I think it’ll be good for me to show you what this thing… (there we go).  So for about two minutes, I am going to show you how we set everything up.  And before we do any filming, we have to put some markers on, and you’ve seen (a little too dark).  What you’ve seen on land-based stuff are these little buttons, reflective markers, they put on.  The trouble is we can’t do that in the water.  So we had to go out and design our own LEDs.  And we taped them on with duct tape, and you can imagine the screams when we take it off—but I’m not around when they take it off.  But we knew this because we really have to put in the different positions depending on what position we film these people from.


So LEDs on.  And then… it takes about half-an-hour, maybe even 45 minutes, because sometimes when we tape both sides, and then we get in the water very gingerly—can’t have them dive-in because we don’t want it being displaced.  And then you will see what the effect is from underneath because it’s very bright then.  So the computer can pick-up the differences, because on an evening, if you do 12 or 16 trials, we can run off about 240,000 data points.  So we can’t do that manually.


These are the cameras.  They’re all high-speed, and they have to be bolt steady: cameras cannot move when you are doing research with high-speed.  So there’s me pretending to know what I’m doing.  And so you can see when the swimmer goes away, can you see the lights?  And so the computer can pick-up the contrast between the dark and the light, and do what we like to think is automatic digitizing.  And most of the time it does very well.  So we don’t have to keep clicking buttons, because 240,000 data points is not manageable, period.  And depending on where we put this.


So once we take all these stuff, then we go into the lab and then we have to digitize.  And that takes again a little horsepower, and this is a still picture.  So, having shown you that, let’s proceed.


Two ways I am going to show you how we look at this.  The first is of course what we call reports from the high-speed software.  The other one that you see are called video enhancement technologies.  And we came up with this way, and I think you will be quite taken-up when I show you what it is.


The reports look like this.  And here’s where I’m going to start-off in making sure you can see, because I’m going to show you a number of these.  The software is very sophisticated because it can interface video and synchronize it with a moving graph.  Now when I say moving graph, you are going to see a line appear, and I’m going to play this.  And you will see this swimmer, and you’ll see a vertical line come-up, just in a second.  And that matches… (no, you need to turn that down).


Yeah okay so you see this moving… (I will disappear).  So you see this moving graph here.  That vertical line matches what we’re looking for, so that is the first thing I want to make sure that we can see.  And you see this line up here, and I’m going to stop it right now.  And I’m going to hand scrub, and you can see where we are.  Now, what we are doing is looking at one major thing and that is: hip velocity.  Everything we do boils-down to how fast our hips are moving….


(What is going on?  Oh, I see: every time we open the door.  Well, we’ll live with it then. [laughing])


Hip velocity really is the bottom line.  And last time… I mean I feel bad because in San Diego I kept saying hip velocity, and people started thinking about the hips rolling and doing all kinds of stuff.  So I made this slide just to make a point: we are interested in the swimmer going from A to B in the longitudinal plane of motion and we want to plot that.  Because everything else boils down.  This is the final variable that we are interested in.  Everything else translates to hip velocity: how our hands are moving; hands, legs, everything, boils down to hip velocity.  So this is a still picture to show what’s happening, alright.  So I’m going to show you plenty of these.


The second thing as I said I call it video enhancement technology, and some of you saw this in San Diego.  And it’s a way we came up with to superimpose stick figures and tracking.  And I have a video here just to show you a sample of this, and I’m going to show you Magnussen and people later.  But this is just a sample to show you what I call video enhancement technology.  And you can see we can track any portion of the body we want and lay down in different colors, so it’s quite a powerful teaching tool.


And the other thing we call segments, which is putting these lines and dots.  Remember this as you can see this is moving video; so this is active video that we can do this.  So we’re quite proud of this.  You can see from a teaching point of view, it’s quite effective. And this has nothing to do with research, this is just an easier way to show things.


Now what we do… there’s two types of research.  One is called comparative, which you get two bunch of groups: one group does one thing and the other group the other thing and then you see what the difference is.  We’re not doing that—thank God.  We are doing observational research.  We have swimmers, we watch them.  And what we are doing now is called multi-2D analysis, which is what people do with gait analysis when they watch people walk.  This is the kind of analysis we do.


And some people say: Oh, you’ve got enough cameras, why don’t you do 3D?  3D may be generating more data, but all you get is a bunch of stick figures.  And if you know me, I hate data and I hate to watch stick figures going around because you can’t see what’s going on—you can’t see beans.  So, multi-2D with the video component I think is critical for us.


And I have a great quote here, so bear with me.  This is by a very famous biomechanist.  He said, “The common notion that scientists are as accurate as possible represents a serious misunderstanding. The trick is to figure out beforehand what level of accuracy is required and then to waste no effort doing substantially better.”  Says Steven Vogel.  Amen to that.


So, let’s look at what I have lined-up this afternoon.  I’d like to show you/talk about four things:

  1. The first one is the maximum hip velocities within each stroke cycle.
  2. Then I want to talk a little bit about impulse—I think the word is starting to catch on.
  3. Then we’re going to look at breakouts. And my apologies to Matt who yesterday insisted that breakouts is not a good term anymore, but we’ll call it breakouts.
  4. And the fourth one is data from a vertical perspective. And you’ll see, it’s our latest toy, very exciting.



  1. Hip velocity

So first let’s look at hip velocities.  And I call it cyclic because the strokes are cyclic.  So we want to see the highest hip velocity during a stroke cycle.  Where does that take place?  And why in the world we need this is because: if you can tell where the highest hip velocity is generated, then you can start falling on the kinds of things that you can alter.  Because if you can do that on a stroke-by-stroke basis, then of course clearly you’re going to see a difference with all the additive effect.


The other thing is this—and you all know this, I’m not telling you anything you don’t know—you need to be able to separate the individual idiosyncrasies of the strokes.  And the better the swimmer gets, the more these idiosyncrasies have to be left alone.  Then you are getting into the art of coaching.  Younger swimmers, more developing swimmers, sure there are basic things we need to work on.  But once you get past a certain level, you leave way-the-heck alone.  And you can come up with a zillion examples of this.


The last point I want to make before I show you these videos is that: when you look at the better swimmers, they’re their own control.  And this is why I personally am getting away from these studies where we get two groups of swimmers and say do this and do that.  And at the end, I’ll show you… a lot of people have been bugging me to talk again about what I did in San Diego about the s-pull and I’ll show you that.  But you can see why those studies, I’m getting less and less enchanted with.


So let’s first look at Freestyle.  This is, again, a continuation of what we found three years ago.  And that is that: the better swimmers are clearly swimming with a straighter arm, more of an obtuse angle.  Here’s two still pictures, and you see what I mean.  And now I’m going to show you the first: this is Magnussen.  When he came last year, they hadn’t done a lot of filming, and so we started filming.  And this is a video enhancement of course, and I’m going to show you what his elbow bend looks like.


And here he comes, and you will see, the guy is about 160°.  I’m going to bring him a little closer before I scrub here.  (Just go back and look at… we saw him here.)  See that, that’s about 160°, that is tremendous.  Same thing with his right arm; look at that.  And they hadn’t seen it too much either.  So they weren’t concerned, because they realized this guy knew what he was doing.  But for our purposes, that’s the first thing I’d like to leave with you.


Then, as I said, a month ago Matt Brown brought his group.  And this is Brit Elmslie who was on their Olympic-gold-medal relay team, and look at her.  Now remember: none of these swimmers were told to swim with anything but a 90° elbow bend when they were first moving along.  So this is Brit and again we have the segments on.  She’s a little wide and that, again, makes these segments quite useful, so you can identify this.  But again let me stop it here.  And you can see, right there, mid-way through her stroke.  Like I said, she’s as little wide, but definitely an obtuse angle.


So we’re going to look at peak velocities; I’m going to show you a bunch of reports now with those moving bars.  This is the one I showed at the very first; this is our first exposure that shocked the heck out of me and everybody else.  And you can see the swimmer.  And again, I’m sorry the graph is washed-out because of this darn LED, but you can see.  This is the first one we showed and we showed this all over—in Norway and all these places.  I showed this at a biomechanics conference first, and they didn’t know what to make of it.


But you can see: the highest hip velocity is in the middle-third of the stroke.  And then as we filmed a number of swimmers as the years went on… this is just another swimmer, same story.  You see then.  I showed you this already as a sample, so I’m just going to play it.  But the middle.


I wrote about it in the chapter in Dick’s [Hannula] and Nort’s [Thornton] Swim Coaching Bible [volume 2].  So that chapter has this and I’ve shown this.  But unfortunately there was a miscommunication with the publisher and they put a graph and makes me look more like an idiot than I am.  [laughter]  So when you see that chapter, this is the kind of graph you should see, not that idiotic thing that came out.  But anyway, c’est la vie.


And in case you still don’t believe this, I’m going to show you Magnussen.  So let’s look at Magnussen here.  And we’ll play it again.  So here’s Magnussen, same story; and you will see his highest velocity.  Now the interesting thing, which I will talk about when we talk about impulse—and I know some of you, I showed you guys this last year, so you’re going to hang with me.  But you can see his pull, his peak hip velocity, lasts for a while; with his right hand.  Can you see that?  It’s not just this little bump.  And I’ll talk about that right after this, in the next focus.  You see that, right there.  But it is in the middle-third.


Now you’re more than welcome to think I’m an idiot, which you’ll probably be right.  But that’s what we see; I’m not manufacturing this stuff.  This is what comes out when we do the filming.  And believe me, I always thought, just like most people, the end of the stroke was where you get this final serge.  But now we can explain it, so that’s much better.


Alright let’s look at Backstroke folks.  And I came-up with this word bi-phasic and I’ll tell you why: you’re going to see two peaks in backstroke.  And then of course I also said: notice the absence of extreme peak velocities during the stoke, and there’s a possible reason.  And if I have a question, it means that I don’t know the answer.


So here is Emily Seebohm; and again I’m going to show you some HD footage with some video enhancements on it, just to get us going.  And this is Emily with the segments on.  And you can see, she has pretty much of a traditional 90°, and she looks pretty good.  So some people are advocating a little straighter, and Matt Brown also said he’s thinking about it.  But you can see, she bends her elbows pretty much at about close to 90; her left arm is a little bit straighter.


If you look at it from the side, look at Emily from the side, this is something that I thought you’d be really interested in.  When we put the trails on, you’ll see she does not go down; and you’re going to be seeing this.  I was quite surprised, myself.  But when she gets into her catch, her hand doesn’t actually sink below the level of her shoulders.  Watch this right here.  Look at that: very shallow but not touching the surface.  So she is doing something that I think most people don’t want to even get close to, because this is flirting disaster if you get too close.  But let me do that again here.  See her catch, very shallow; isn’t that interesting?  So she does not dip in.


And then in contrast, I’m going to show you Sophie Edington, who came on the way to a Pan Pacs, I guess in 2010 in Irvine and she won the 50 back.  But she does a lot more down and up.  So I though it will be fun for me to show you Sophie’s pull here, with the trails on so you can see just how much she goes down and then comes back up.  Which is what most backstokers are doing, I guess.  Again, since I’m stuck out there in the colonies, you need to bring me up-to-speed sometimes.


Alright, so let me now get on to Emily’s.  This is the high-speed stuff, and you can clearly see.  I’m going to play it and then I have two still pictures to show you.  So let’s… (I’m going to scrub Emily because she took a while getting towards where we needed to film her).  And you can see, as she comes-in now, look at the bottom one please because the top one the camera didn’t coincide with the pull but the other arm did.  So here’s… can you see the first peak, right there, where her hand is?  And then the second peak at the end of the stroke.


So to make it a little bit easier folks, I made two still pictures with the bar at the first peak, which is the middle of the stroke, and then the second peak at the end of the stroke.  So it looks like backstroke, as I said, is bi-physic—that’s my term, so you’re welcome to dump it.  But that’s what we see in backstroke.


And so just as a recap, I’ll play this real quickly and show you.  This is the freestyle, and you’ll see the bars come-up.  I’m just going to play it here while we talk; same thing I showed you earlier.  And you see the bar which is a single peak, it looks like, in freestyle.  And then in backstroke, we have this clear difference of two peaks.  So I think it’s something to think about.


And to make a case for really thinking about it I’m going to show you a swimmer, next here.  You can see… it’s a little hard to see because this is so washed-out—and boy, I’m sorry these lines are washed-out.  What you will see is this guy is anything but symmetric: he pulls higher with one hand in the middle, and the other arm, higher on the other side at the end.  So who knows.


But I think the lesson for us is that: don’t think that they’re instinctively going to do the same thing on both sides.  There’s no symmetry; none of us is symmetric, particularly when you come to unilateral strokes.  There’s no way you can expect the same thing to happen on both sides.  And I mean that in all sincerity; you must pay attention to both sides.  (Again, sorry this thing is washed out—I don’t like to apologize, but that’s it.)


Alright: Breaststroke.  Again, bi-physic because you’ve got a pull and a kick.  So let’s watch, again just as an intro, this is Leisel [Jones]; and you will see what she does.  And we can put these video-grids on, just so we can see how symmetric she is, or symmetrical.  And that’s Leisel looking very symmetrical.


And then from the side—and I think I showed this to you guys in San Diego—this is fantastic footage because it shows you what world-class breaststroke looks like from the side.  We’ll bring her up, and then I put the segments on; and if you want to see a streamline, just wait a stroke.  Here she goes right here; this is amazing.  I’m going to actually stop it, right here, to show you what streamline looks like.  Look at that; not bad, huh.  That’s why, I guess, she was the World Record holder.  So you can see the segments help us really visualize and see what things are going on.


Now, when we just had a breaststroke just pulling-only, here’s what we saw.  And I said maximum pull occurs in the in-sweep near the completion.  So we isolated the pull, and let me play it here for you.  (And, thank God, we can see the bars a little bit better here.)  But you can see… and I’m going to talk about that vertical view at the end, but you can see, this is our latest toy and you can see why we’re excited about it.  But it’s an amazing view we can get when we synchronize from the bottom.


And what you’ll see is the peak somewhere at the end of the in-sweep, right as they’re coming.  You see that?  So let me stop it right here, and hand scrub.  So you see, this is only pulling now; she’s got a pull-buoy on.  Her peak with her arms come-in as she’s bringing her hands in, ready to translate or transition to the forward.  Then there’s this lag.  And then you can see it happen again; you can see the pull-buoy on.  But can you see where you get the peak, right there?  And if you see from the underneath, you’ll see just where her elbows are in terms of wingspan and I’ll talk about that.


Now when you look at the whole stroke, I said in this swimmer, maximum velocity also appears to occur during the in-sweep.  However, watch the drop in hip velocity between pull and kick—and this is pretty interesting, folks.  Look at the bottom graph, okay.  I’ll talk about the top graph later on, but look at the bottom graph.  And you can see when she takes her pull, it’s just like we had showed you before…. (Where is she?  Let me… sometimes the swimmers take a little while to show up.  And see now you know: where the cameras are still, they’ve got to show up.)


But here she is and now you can see her pull, right there.  You see the pull on the bottom, you see the peak right here.  And then she stretches out, and then you see the next little peak.  But watch, this is what’s really interesting: look at how much drop-off there is when she’s recovering and bringing her legs up.  And I’m going to talk a little bit about that later as well.


But isn’t that amazing: how much we lose?  So the moral of the story I think is: you’ve got to get them to bring their feet up pretty quickly; there’s no dilly-dallying when your legs are coming up.  I think most of you know this, or all of you.  But you can see visually how killing, in-terms of hip velocity, this period right here is; it just drops your velocity big time.  So as I said peaks and drop-off in velocity in these swimmers see high contribution.  And here is a still picture; look at that.  So that’s what we’re looking at.


And here is another video, of Dan Tranter who made the 200 IM for the Australian team.  And you see the same thing. (I’m going to go a little fast here.)  But watch his video.  You see right here, right at the in-sweep, and then look at the drop right there.  So I guess something to work on.


Alright, the last one I’m going to show you is Butterfly.  And just as we expect, that peak velocity occurs right as you come in.  So let’s just play this so you can see what it looks like.  (And again I don’t want to wait for the little guy to show up.  So here we go, right here.)


And you can see the bars show-up right as he comes right there.  So, just as we expected, this is no surprise: the highest velocity is right as you’re ready to push the heck backwards.  See that at the follow through, right there.  And that again, as you can see, there’s really no surprise.  What is surprising is the drop-off, again, during the recovery.  And I’ll show you one other swimmer—who I’ll show you later on as well—and look at that drop off here.  Here he is right here.  You can see where the peak is.  But look at this: when you bring your legs up, for ready for the down-beat and your arms are going through the air, look at this drop-off.  Tremendous; it’s really something.


If you work… I mean, I’m sure all of you working with flyers, you’ve got to pay attention to how long it takes to bring your arms up and get ready for the next kick.  It doesn’t look like the amplitude has to be big at all.  You’ve got to figure out some way to get the amplitude of the kick smaller, so you can get around and not have this tremendous drop.  And here is the still picture, of that too.  I hope you’re impressed, or depressed.



  1. Impulse

Alright, focus two, I call impulse.  By definition… again, I don’t want to put you to sleep.  But by definition impulse is force times time.  And the majority of land-based activities reward application of force, high forces, for either brief or extended periods.


So I had fun finding some examples here in still pictures.  This is a high force in a very brief time: for pitching, throwing a ball, hitting.  And then I was trying to find something, and wracking my brains, to find a high force for an extended time and obviously it hit me: wrestling is a great example.  Of winning the gold medal, if you can exert a high force for a long time, so you’re opponent gets tired.  So that’s an example of land-based impulse.


Now starts and turns of course has a trade-off: you’ve got to push hard, but it’s got to be fairly brief.  And so I have these two pictures just, again, to impress you.  But, in Swimming, when you’re actually swimming, there’s some very interesting things.  Again, some of you bear with me, because I talked about this last time: when I was here in Las Vegas, I showed you guys this.


And here’s Magnussen, and I showed you his right arm.  And now I’m going to play this, and show you the difference between his impulse on his right arm and his left arm.  So here goes.  (And again, let me hand scrub.)  So here’s his right arm pull; you see that?  Right there.  And then you see… there’s a drop-off here during the transition, and then you see his left arm: much smaller, a little bump.


So I’m going to give you some numbers which are going to be impressive.  His hip velocity was the same, on both sides.  You see that?  Virtually identical.  But look how long his hand held the water on both sides: big, big difference.  So I put these numbers in here next to the picture.  He held the water with his right hand almost twice as long; maintained the pull, almost twice as long.  So that’s what impulse is folks.  So if you’re thinking about it with your swimmers, you must make sure that in the optimum time they’re holding the water for as long as they can.


And just for your interest, we showed them this about six o’clock in the evening and the next morning the guy worked on this and pushed a 22.9.  So… something.  I guess he was reasonably impressed.


Another example of impulse is six-beat versus two-beat.  And here we had this girl Jessica who made their 800 free team, and I think she almost made the final in Barcelona.  But this is her two-beat kick, and you would see this fluctuation.  Can you see the impulse of her hips when she goes fast?  (Again, I’m going to scrub.)  Her hip velocities are very up and down; can you see that?  She has a higher hip velocity and a low hip velocity because she’s kicking a two-beat kick.  Look at her six-beat kick.  You see how much longer she’s able to keep that hip velocity?  So again her impulse has changed, fairly dramatically.  She can maintain her high hip velocity for longer when she’s kicking a six-beat kick.


Again, you guys know this stuff, as I said; you know this intuitively.  Now we can put some numbers on it and make a little bit more sense of it.  So here is the difference: 0.2 seconds per stroke cycle is what she was able to do when she kicked a six-beat.  Now you multiply 0.2 times the number of strokes it takes for 800 and you can see the potential.



  1. Breakouts

Let’s go to breakouts.  This is of course the period of the time between taking the first pull and the head-break.  And so what we want to look at is the timing of the first underwater pull and fluctuations in hip velocity that accompany the kick and the pull.  And you want to make sure they’re sustaining kicks.


So here’s a good breakout.  And you can see what a good breakout looks like.  I think we all have a very good idea that in a good breakout we don’t want to lose velocity.  And I’m going to just play it; I’m not going to scrub it by hand, I’m just going to play it.  (Is it moving?  Yeah.)  So watch now, the swimmer is going to appear.  And you’ll see the bar and you’ll see the two lines here: this is when the pull begins and that’s the end of the pull.  So here we go.


So he takes his pull.  And right there, here comes the bar, pull starts.  Pull ends.  And velocity keeps continuing.  So nice, uninterrupted.  Here’s the bar, so this is where the pull starts.  And then you can see the head-break, right here.  And then he continues to increase speed as he continues through.  So that’s all well and good.


You’re ready for some other choices?  Here’s an early breakout.  Again, you better be ready to swallow hard.  Look at this curve: this is anything but what you just saw.  So here we go (and again I’m going to bring him up a little faster here).  And here’s the first pull, right here.  Now remember early breakout, I want to clarify, is when you take your pull and you’re submerged and you’re waiting to surface.  So you’re taking your pull too soon, too early.


So here we go, he’s taking his pull.  And of course, there’s going to be an increase in hip velocity; he’s taken his pull, so he better go a little faster.  However, he’s still underwater.  So hanging out in the water, look what happens.  You’re waiting; waiting for good things to happen, but it’s going to take a while.  And so this is when the head-break occurs, after you lost velocity.  And putting the numbers in: 31% drop-off in this case; for this particular swimmer, lost 31% of his hip velocity because of that early pull-out.


Late breakout is after you surface; you’ve waited way too long.  So here we are, you can see: take your pull, we already surfaced—that’s what this says.  And then all this stuff is happening because you’re hitting wave drag, which is as you know so devastating.  So you can see as soon as he’s on the surface, you’re not going to go fast because wave drag is going to take over.  So all this stuff you see right down here is because of wave drag.  Then you do a little kicking, you’re still hanging out, and then you take your pull, and then you get going.  So the drop-off is just as dramatic, about 36%.


So either extreme is not good, as we all know.  But now at least we can see some numbers and we can relate to that.


And since Magnussen is somewhat the man of the hour, let’s watch his breakout.  And you can see: pretty decent.  And here he comes… I’m going to let him do his turn first here.  And now he comes off.  You can see here’s his pull, there’s his head-break—a little lag, a little drop off—and then maintaining the speed.  So much better surfacing.  So a pretty decent breakout.


Now since Matt [Kredich] talked about turns yesterday, I thought I’d put this in.  For one reason only and that is: I wish life would be just as easy as we think it is.  But I thought—and maybe I was mistaken, but—he was talking about maintaining the speed off the wall.  It’s a lovely idea.  But there’s no way in the world—unless you’re on Mercury or someplace—that you’re going to do that.  The instant our feet leave the wall, your velocity is going to drop.  Because unless they got an absolutely lousy push-off and there’s something seriously wrong with their knee extension strength, there’s no way in the world you’re ever going to maintain the same speed.  That’s it; that’s just an anatomical fact.


And so you can see Magnussen, right here.  The moment his feet leave the wall, right here, this is the peak velocity: when his toes left wall, right there.  Can you see that?  And from then on, goodbye Columbus; okay, that’s it.  You’re never going to do that.  So it’s a lovely idea, and if you want to talk to your swimmers and make them think they can do that, I think it’s wonderful; as long as you know, in the deep recesses of your mind, that it is impossible.  Okay?  [laughter]



  1. Vertical perspective

Alright, last thing: vertical perspective.  This is our latest toy, and boy, the pictures we’re getting are incredible.  This is the camera that we use; we lay this at the bottom of the pool.  And I’ll show you a composite of… my wife loves this kind of stuff, so she wanted me to put all three pictures together.  But I think it turned out pretty good; watch this.  I’m going to play this, and you’ll see up here, this is a guy doing just breaststroke kick then there’s a guy doing fly, and then I’ll show you the last one.  But this is really neat to see.


This is the look we get from below.  Now remember, we’re synchronizing this with all the cameras, from the side and from head-on.  But that’s the vertical view of breaststroke kick, then here’s a flyer coming-up.  And as you can imagine, what you see is the best of multiple takes, because the swimmer has got to be perfectly lined-up with the camera.  And, boy, some swimmers just don’t get it.  [laughter]  So: welcome to research.  I tell them, “Hey you’re participating in some research that nobody is doing.”  But here’s Emily; and Emily to her good fortune, boy she knew what to do and so she nailed it.  You can see her pulling.


The new software we have cramped-down the screen a little bit, and we’re going to change that as soon as I go back.  But you can see, from the bottom you can get a really-nice view of how the pull looks.  So you can imagine when we start to synchronize the camera from the side and from head-on and from the bottom; boy, we’re going to see a lot of good stuff.


And some of that stuff, I wanted to just share with you.  What we’re really looking for are widths and amplitudes of the pull, particularly in the breaststroke and the butterfly.  Breaststroke wingspan: how wide should we go, and how much should we come in.  So how wide at the end of the out-sweep?  And the effect of a rounding-out early?  And I just put this in here: comparing the traditional pull with the shorter, earlier rounding-out as in the in-sweep with Rebecca.  So those are the kinds of things that we have the potential to look at.


And here is the picture I showed you, again, of the girl, just to show you how we can measure wingspan, folks.  You can see, when she pulls, that’s her wingspan.  Can you see that?  So we can measure how wide the hands are going on the out, and then, of course, when she comes in we can measure that as well.  So the software is great—it better be great: it’s $15,000 dollars.  But you can see.  So we are very excited to be able to start doing stuff like that, and that’s where we’re going.



Then the last thing I want to show… oh, I’m going to show you a little breaststroke kick here.  Advantages of the whip kick.  Here’s Leisel, going away from the camera.  I thought it’d be great to show you how even she is; she’s got very symmetrical kick.  And with the trails you can really see that—they are beautiful.


But here is just the kick.  We had one of the breaststrokers on the varsity team just kick breaststroke.  And you can see this is really interesting.  That’s the first kick in.  But you see the real kick at the end.  When you see the draw-the-legs-up, you see how the velocity drops off.  And then as you kick.  So we can measure… again, look at how wide a good kick is versus the old wedge kick, and play around with it.  So we’ve got a lot of things we can do, and we are looking forward to it.


The last thing I have for you is a beginning attempt at looking at why we are now doing the straight pull versus the keyhole pull.  And I want to give Steve Haufler here: Steve, I still call it the diamond pull, because I like the idea of a diamond.  But I guess a lot of people are just calling it the straight pull.  And I’m going to show you something that I think you’ll be reasonably impressed.


Here’s… this is one of our swimmers, Dan Worden, who is a flyer.  I asked him to go back in time and do a keyhole pull.  So here he comes in (and again, in the interest of time folks, I’m going to hand scrub, so bear with me).  But here he comes with his keyhole pull, right here.  Can you see where his hands are?  Coming very close, underneath his chest.  And you see where his peak is?  Right here.  Then he has a terrible drop-off: you see how his velocity has dropped-off when he’s recovering and getting ready for that upbeat.  So we want to do something about that—you guys do something about that, I’m out of this.  [laughter]


But here he’s again, with the straighter pull.  And you’ll see: look at how different that curve looks.  So what are we talking about?  We are talking about impulse folks.  When you’re doing the keyhole pull, you get this massive surge right at a very short time.  But when you’re doing the straight pull you look like you’re holding the water and keeping that velocity for a longer time.  And I thought… I got excited, I hope you get excited, because that’s the reason now you are going faster with fly with a straighter pull because you can hold and exert more impulse for a longer period of time.  I hope you can see that.


Let me go back here.  You see how much longer you look like you’re holding it?  And here’s a still picture I made.  The velocities are the same, but one is lasting for longer time.  Again, going back to the idea of impulse.


Alright I hope I gave you plenty of things to lose sleep over. [laughter]



Now I want to change tactics a little bit; this is fun stuff.  Since a lot of you, I think, use monofins for training.  Last summer, we had a young man come in, 18 years-old, on his way to college.  Dynamic apnea; these guys are absolute nuts: there are the guys who go deep and turn upside-down to flush their sinuses with salt water so they can go even deeper and all that stuff.  Well one of the records is dynamic apnea, which is a fancy word for: how far can you go under water up and down.  And they allow these fins to be used.


So he came and trained, because he wanted to break the American Record for dynamic apnea.  So I’m just going to play this just to give you an idea what it looks like.  So he came and he trained for six weeks.  The American Record was 175 meters underwater.  And after six weeks—boy, the guy did great—he went 200 meters.  They had to fly in all these judges to our pool.  But I got to film him.


And you can see, the way these guys kick is to conserve energy; they do two kicks and then they pause.  And they get that momentum.  I told the coach, I said “Remember, that pause, the moment you stop your losing momentum.  The moment.”  So he said, “Yeah, yeah, I know; but if he keeps kicking, he’s going to get more tired.”  Which is fine.  There he goes and there, see, he pauses.


And here is when we put the trails and segments on; it turned out to be quite spectacular.  We put a trail on his fingertips, his hips, and then the back of the fin.  And you can see he did a really nice job with his hips; boy, not much undulation.  But the fin, of course, this gigantic thing moving up and down.  Visually, it looked pretty fancy, but that’s what it looks like.



Alright, now, last thing I want to talk about, again: this business of statistical significance.  And this is why I’m getting less-and-less enamored with these Swimming studies.  And to make a point of it, there’s a bunch of people—I know you guys are in the audience too—kept bugging me about showing this s-pull stuff again.  And I call it the infamous s-pull; my wife said “Don’t call it the infamous s-pull.”  I said, “No, sorry.”  It’s infamous, because as I said—and again, I hate to recycle old jokes, but—the s-pull is like the nine-headed hydra: it refuses to die.  So no more s-pulls after what I show you here, I hope.


We asked this girl to purposely do an s-pull.  (I showed you this in San Diego; so if you haven’t seen this, this is great.)  So here she comes along, you see where her hip velocity is, on the top.  And the moment she starts to go out, look what happens: the hip velocity drops.  See that?   Let me show this to you again, just in case you were not impressed.  Right here is her maximum hip velocity, you see that?  But she starts to veer-out to the side, and look at how her hip velocity drops.


So we asked her to do the s-pull.  Then, of course, as she starts coming underneath, now she’s going to get back some velocity.  I mean, talk about predictability; this is nothing magical, this is exactly what happens.


So here’s a still picture of that in case you still didn’t believe in….


[audience member]:  Can you play it again?


[Prins]:  Okay.  So here she goes.  And the bottom graph is the way we measure how wide the hands go: the red line on the top is where she starts from, so you can see this.  So you see: you don’t want the s-pull to come close to you or your team; keep it away.  Can you see what happens?  Now this is the distance; we can measure with the software from the center to how far her hands went.  So we can say how far you can go without having this drop-off.  And I’m not going to do that soon, because I’m fed-up with the s-pull as it is, anyway.


But the whole reason is this.  And we talked about it, I wrote about this.  But it’s the misunderstanding that cropped-up, we are trying to interpret a three-dimensional movement in two dimensions.  When you see an elliptical path and you put it on a flat piece of paper, of course you are going to see this back-and-forth movement.  But that is not what you do, that’s what occurs.  And that’s the mistake that originally came-about and that’s what continues.


And so, talking about statistics, I presented this stuff last year in Australia at this biomechanics conference.  And we had 18 swimmers and we didn’t find any statistical difference.  Are you telling me that means that there is no difference?  We know, us in the Swimming business know, that that is absolute rot; if it’s 1/100th of a second, that will make a major difference.  So that’s how I feel about statistics.  And as you know, there is a famous quote about statistics: there’s lies, damn lies and then there are statistics.


So I want to thank some people who helped; these are my crew here, long suffering, which is great.  And then last thing I want to do is a shameless-plug here and that is: we are building a website, Swimming Biomechanics.  And I’m going to show you kind of the skeleton of it and in November, I’m hoping, we are going to have a whole bunch of about 30 video clips with the high-speed stuff and the video enhancements on the website, that you can go on and I’m going to charge you the earth-shaking amount of $10.  So for $10, you get to see all this stuff.  Good things, no cheap, sorry.  So keep track of it, and if you need to get a hold of me this is my email address.


I want to show you, this is my grand finale here, and this is a great cartoon that I found in The New Yorker.  If you can’t read it, I will read it for you.  It says “Einstein discovers that time can stand still completely.” And you know, he is sitting at the airport.


So thank you very much.  And I hope I gave you some things to think about.  Thank you.



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