Archive for November, 2007

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Rules? We Don’t Need No Stinkin’ Rules! (Figure Skating)

November 21, 2007

If you’re reading this blog post, the chances are you’re a member of the figure skating community.  As such, you probably take many things about this great sport for granted.

Whether you’re a spectator, a skater, a skater’s parent, or even a coach, I’ll bet you assume that the most critical aspect of our sport has very clear definitions and rules.  What is this critical aspect?  Jumping, of course.

It seems logical that everyone knows exactly what an axel is.  Or a toe loop or a lutz.  In fact, it seems logical that there would be legally binding definitions and rules regarding each of these elements.

But quite astonishingly, there aren’t!

How do I know?  Because I’ve been doing some surveys of coaches at SkatingCoachQuiz.comI’ve been asking the coaches there for precise definitions of “perfect” jumps. And the survey results are all over the place.

This really got me wondering:  Why do coaches disagree so universally regarding precise definitions of jumps?

I figured I could help clear up the confusion by digging out the formal, legal definitions and sharing them with the coaches.  But what I found, really surprised me.  And disappointed me.

There really are no formal rules.

Don’t believe me?

If you own an official US Figure Skating Rulebook, you can read it from cover to cover and you won’t find a formal written definition of any of the jump elements.  The best you’ll find is the amusing and childish “List Of Jumps” at the start of the Glossary.

You may say, “Well, all you need to define the jump is the entrance edge, the exit edge, the total rotations and whether there’s a toe assist or not.”  But I’ll immediately argue that that definition is really weak.  It says nothing about the critical moments just before, during and after lift-off.  It also says nothing about the critical moments just before, during, and after touch-down.

These critical moments remain blissfully undefined.

Not sure what I’m talking about?  Everyone agrees the entrace is a back inside edge because the rules say so.  But from there on, nobody seems to agree on anything…most likely because there are no rules!

  • There are no rules to state whether it must be a clean edge take-off or whether the skater may push off the toe pick of the skating foot at lift-off.
  • There are no rules to state whether the skater must take-off facing backwards or whether the skater can pivot forward before lifting off.
  • And if a skater is allowed to pivot forward, either doing a very short three-turn or actually spinning on the toe pick or blade, how much pre-rotation is too much.
  • If a short three-turn is allowed, can the three turn exit edge touch the ice or only the toe pick?

Due to it’s artistic nature, figure skating is a very subjective sport.  But are you starting to understand that even the technical aspects of figure skating are totally subjective?  There are no written rules!

Still don’t believe me?

  • In a step sequence, exactly how long and how deep must the edges be for the skater to get credit for a rocker or a counter?  Don’t bother looking that up…there’s no rule for it.
  • In a sit spin, the bottom of the seat must be below the top of the knee, but how exactly is the bottom of the seat defined?  Last time I checked (on video today, by the way) the seat is curved, making my estimate of “bottom of seat” totally different than someone else’s.  Again, there’s no rule for it.

The added complication of the new International Judging System was justified by claiming that it would be more fair.  But can you see how the lack of precise definitions means that even the technical aspects of skating are totally subjective.  We are now using frame-by-frame video analysis to judge our competitions.  Every aspect of take-off and landing can be reviewed.  But with no formal definitions, the results of those reviews will depend on the subjective opinion of the technical team.

It’s probably pretty clear from the tone of this post that I think this is completely unacceptable.  When I have some time, maybe I’ll submit some formal definitions to US Figure Skating and to the ISU.

My goal is to help coaches teach better.  But that’s close to impossible without formal definitions and rules for the elements we teach.  Today good technique and biomechanics for one coach are totally unacceptable to another.

If we can formalize the rules, we can also formalize the technique.  Of course, many coaches don’t want that.  Some don’t want to learn new technique.  And some successful coaches don’t want the technique they teach to be standardized…because their skaters will immediately have a lot more competition.

Whether you’re a coach, a skater, a parent, or a spectator, I’d love to hear your thoughts on this so please leave a comment by clicking the No Comment/Comments link below.

Trevor

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Initial Test Of Vertical Jump Measurement Methods

November 18, 2007

Continuing the discussion from my last post (Double Axel Barrier), I’ve been able to run two tests so far with mixed results.  Recall that I’m trying to determine if flight time measurements made using video analysis software such as Dartfish or Pro-Trainer (a low cost Dartfish substitute) can be used to estimate jump height.

As stated in previous posts, sufficient flight time is a critical component for figure skating jumps.  For example, in order to get enough rotation to land a clean double axel, the minimum flight time needs to be about 0.45 seconds.  Based on some physics calculations (basic projectile motion), I’ve been estimating the required height at 10.5 inches (0.467 seconds).

My ultimate goal is to see what percentage of the female population is physically capable of landing a double axel.  To do that I’ll need to correlate the flight times with standard vertical jump statistical data.

The first part of the test is as follows:
1. Skater stands next to wall and reaches up and makes a mark with one finger (using chalk or washable marker).
2. Skater stands on tip toes near the wall and makes another mark with same finger.
3. Then skater fully bends and jumps up off two feet as high as possible, slapping the wall and making another mark.
4. Step 3 is repeated until skater has a consistent pattern on the wall of maximum jump height.
5. The standing mark is considered the baseline.  The tip toe mark and the maximum jump height are measured from the baseline.

That gives us our “standard” vertical jump measurement.  This is the most common method used for measuring vertical jump.  Statistical data is available based on this measurement method as discussed in a recent post.  (The tip toe data is necessary for correlating with flight times and is not part of the standard test or available statistical data.)

Next, the video method is used.  For the video method, the capture software is turned on and:
1. The skater jumps multiple times facing sideways to the camera.
2. The skater jumps multiple times off one foot, using a natural “leg through and lift” technique.
3. The capture is stopped and the flight time for all the jumps is found.  (As discussed in post Are Figure Skater’s Projectiles?, the flight time is measured from the first frame the foot completely leaves the ground until the first frame when the foot touches the ground).

I performed this test with 2 skaters.

Skater A:
Baseline to tip toes:  2.9 inches
Maximum vertical jump off two feet at wall:  10.5 inches
Maximum flight time off two feel on video:  0.450 seconds (video shows flat footed landing)
  Corresponding jump height estimate from video:  9.8 inches
Maximum flight time off one foot on video:  0.351 seconds
  Corresponding jump height estimate from video:  5.9 inches

Skater B:
Baseline to tip toes:  3.1 inches
Maximum vertical jump off two feet at wall:  13.4 inches
Maximum flight time off two feel on video:  0.450 seconds (video shows flat footed landing)
  Corresponding jump height estimate from video:  9.8 inches
Maximum flight time off one foot on video:  0.450 seconds
  Corresponding jump height estimate from video:  9.8 inches

These results are clearly not conclusive.  Each skater only made three attempts for each measurement and the measurements were not always tightly clustered.  For example, Skater A had two foot flight times of 0.417, 0.451, and 0.433 seconds while Skater B had two foot flight times of 0.450, 0.434, and 0.451 seconds.  Skater A had one foot flight times of 0.317, 0.334, and 0.351 seconds while Skater B had two foot flight times of 0.400, and 0.450 seconds.

In future tests, each skater will perform more attempts to get a better estimate of the maximum.  When I have more data,  I’ll see if I can correlate the results and add in factors for take-off from tip toes and landing flat footed.

Also note, that some skaters will be able to jump just as high (or even higher) off one leg versus two, while other skaters clearly lose significant height jumping off only one leg.

I’m not sure this will be useful to you yet, but it just keeps you up to date on some of my testing.

Trevor

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The Double Axel Barrier… And Female Athlete Vertical Jump Statistics

November 7, 2007

As my loyal readers know, I’m very interested in understanding the athletic and physical limits associated with figure skating jumps, particularly for female skaters.

One of my goals is to understand what percentage of the female population has the athletic ability to do a double axel.  As I’ve shown before, the double axel is a huge dividing line for most skaters.

The next hardest jump, the double lutz only needs about 0.36 to 0.38 seconds of flight time based on video analysis (using Dartfish and simlar programs).  I’ve actually measured flight times on clean double lutzes as low as 0.34 seconds.  But using the 0.38 second number and using the table in a previous post on this blog (Are Figure Skaters Projectiles?), the double lutz needs to be about 6.5 inches high.

The double axel needs to have about 0.467 seconds of flight time, although I have measured ones with as little as 0.45 seconds.  Using 0.467 and the jump height chart gives about 10.5 inches as the minimum height for a double axel.

So why is this so important?

Mainly because based on my observations, most female figure skaters cannot jump 10.5 inches off the ice.  They just don’t have the physical ability to jump that high off one leg, regardless of technique.

To understand what I’m talking about, here’s an example.  Consider an ‘average’ 13 year old female skater.  According to the statistics, an average 13 year old female can jump 11.5 inches vertically off two feet.  This distance includes the ankle extension while still on the ground.  Estimating the distance of the ankle extension as 2.5 inches, that makes the true vertical “jump” or vertical distance in the air for the average 13 year old female only 9 inches.

And remember, that’s off two feet.

What are the statistics for one foot?  I’ve been unable to find any statistics on this so I’m running a study to determine this number so I can correlate it with the existing data.

But for the sake of argument, let’s say a skater can only jump 80% as high off one leg as off two.  That gives the average 13 year old female a potential jump height of 7.2 inches (0.8 x 9 inches = 7.2 inches).

And since a double lutz needs to be only 6.5 inches high, the average 13 year old lady skater clearly has the physical ability to do it.

So if the assumptions are reasonably close, we can see why most female skaters with average athletic ability or above can get through double lutz.  But we can also see why average female athletes have no chance at a double axel.  Their vertical jump off one leg is nowhere near the required 10.5 inches.

OK, just for illustration purposes, based on the assumptions above (2.5 inch ankle extension, 80% height off one leg), how good of an athlete does a 13 year old lady need to be for double axel?

If the jump needs to be 10.5 inches high and the ankle extension is 2.5 inches the skater needs a vertical jump off one leg from a standing position of 13 inches (10.5 + 2.5 = 13).  If the 13 inches are off one leg, then the skater needs to jump 16.2 inches off two legs (13 / 0.8 = 16.25).

According to available statistics, a 13 year old girl that can jump 16. 2 inches off two legs is in 97th percentile.  That means that only 3% of this age group can jump higher.

Wow!  Guess what that means?

If all the assumptions were reasonably close, only 3 percent of 13 year olds ladies have the athletic ability to jump high enough to do a double axel.  Now I’m sure this number is too low but it illustrates my point.

It should be clear why so few female skaters get a double axel.

OK, just for completeness I need to be very clear here.  I pulled the 80% number out of thin air.  And the 2.5 inch ankle extension number is a conservative estimate based on a handful of measurements ranging from 2.25 to 3.5 inches.  But these numbers need to be investigated.  And I plan to do that as part of my vertical jump study.

Also, the vertical jump numbers for 13 year old females was determined using an Online Vertical Jump Calculator.  And as elite skating coaches will confirm, a skater can actually jump higher on the ice with good technique due to the ability to use the speed of jump entry to vault the jump upward.

In other words, there’s a lot of assumptions here that need to be investigated further.

I hope you find this information useful.  As coaches, we need to stop having our skaters attempt jumps that they don’t have the vertical jump ability for and they simply have no chance of landing.

Trevor

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Figure Skating Coaches Need Discipline

November 2, 2007

I wanted to make a comment about how much discipline and patience we need as skating coaches.

Today I worked with a low-level skater on a her scratch spin.  I work with this skater in private lessons on a fairly regular basis.  This skater is currently in a basic skills program and is learning a scratch spin in her class.  But I’ve been very unhappy with the technique she’s been learning in class.

Unfortunately, she’d been having some success with the poor technique, spinning about 3 fairly centered rotations.  What I disliked about her technique was she was taught to simply twist into the spin, while I wanted her to glide on a long entrance edge to allow longer, faster spins.

This put me in an awkward position.  I had to convince her to try it my way without openly criticizing her basic skills instruction.  Not surprisingly, when she initially tried it my way the results were terrible because she could not control the entrance edge.  It took multiple lessons over several weeks of patiently and gently demanding the technique I wanted before she started to “get it.”

And today was the breakthrough!  Today she could finally control the edge as it got deeper and deeper until the edge naturally turned into a spin.  Her spins today were nearly centered and she was now getting 6 full revolutions.

With today’s success, I could see that she finally “bought into” the technique I was teaching her.  Up until today, she was merely humoring me.  She was willing to try what I asked, even though it wasn’t working, because I remained utterly unshakable in my requests.  This is the discipline I’m talking about.  We need the discipline to ask a skater to do the proper technique every single time.

Too often I see coaches throw away a valuable 15 minute lesson of technically improving drills by giving in to the skater’s desire to try the element when they’re still not ready.  Often coaches are giving in to their own curiosity or lack of patience.

I once took away a skater’s axel for 3 months.  At the time, she couldn’t get her free leg in front before jumping.  We used the three months working on exercises to slowly and persistently change her technique.  By the end of the three months, her new technique was totally ingrained in muscle memory.  Her technique was fixed from the very first axel she tried after the 3 months.  And it was permanently fixed!

As coaches, it’s our job to be patient and make sure the technique is good.  Skaters rarely have any patience.  And their parents are usually even worse.  As coaches, we’re the only voice of reason in the process.  The problem is, as coaches we’re likely to give in to our own curiosity, the skater’s pleading, and the parent’s pressure.

Stay strong!

Trevor