Archive for the ‘double axel’ Category

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Figure Skating Jumps – A Review of Minimum Air Times (Trevor Laak)

July 2, 2014

With the prevalence of low cost video analysis apps on mobile phones and tablet computers, video analysis of figure skating jumps is within reach of EVERY coach and skater. Past research into minimum air times for each jump can now be used by all figure skating participants to help assess skater progress and minimize injuries.

To my knowledge, no formal publication of jump minimum air times has yet been made. However, a large number of researchers including this author have compiled statistics on minimum air times that should provide helpful guidelines for those interested.

I have received a huge number of requests for this information so I hope this post addresses the interest in this topic.

 

Why Minimum Air Times Are Important

Knowledge of minimum air times is important to coaches because it provides a relatively clear way of assessing a skater’s athletic progress and technical progress with any given jump. If a skater is matching or exceeding the minimum air time for the jump and has solid technique and an appropriate body type, they should be able to get close to full rotation of the jump under ideal conditions.

Air time information serves two important and related purposes in the development of figure skating jumps.

1. It reduces the pressure on skaters to complete elements that they physically have no chance of completing, and

2. It dramatically minimizes injuries from attempting jumps a skater is not yet ready to attempt.

Skaters have historically been under extreme pressure to land more advanced jumps at younger and younger ages. As the sport progresses technically, this pressure is only continuing to grow.

How many skaters feel guilty about not landing their double axel (or any jump) after working on it for months or years? Skaters often feel that they are letting their parents and coaches down and they often experience extreme frustration at themselves for not learning a new jump sooner.

But minimum air time measurements can help to reduce this guilt and frustration. If a skater knows she or he is not jumping high enough to land a jump cleanly, the focus turns to solving that problem rather than remaining fixated on just landing the jump.

Similarly, coaches can help their skaters dramatically reduce injuries by knowing their skaters’ air times and not expecting or demanding that the skater stand up and land the jump when they are simply not ready. It then becomes the coach’s job to help the skater optimize jump technique and develop the necessary jump height through off-ice training.

The days of repeated futile jump attempts are over, or at least they should be. In this day and age, no coach should continue to apply the just-stand-up-and-land-it mentality without knowing air times.

How These Numbers Were Generated

The minimum air time numbers for each of the major figure skating jumps provided below were compiled from measurements of many jumps over a long period of time. By measuring air time on as many jumps as possible over a period of many years, certain air times stand out for each jump.

Some of the measurements were made on practice jumps videoed directly by a coach or skating parent while others are a result of digitizing televised broadcasts of competitions or other events of elite skaters. Historically, a televised skating competition or event could be recorded and then digitized to provide model jumps for analysis.

 

Caution With The Numbers

It should be noted that attaining minimum air time does not automatically mean a skater should be able to land a given jump. Minimum air times are typically only possible by skaters with extremely efficient technique and an optimal body type.

Skater body type plays a big role as smaller and thinner skaters typically have an advantage for faster rotation. Even this is an over-generalization because some tall skaters can rotate very fast, but as a general rule, it is small and thin skaters that these minimum air time numbers were generated from.

Thus, larger skaters or those that have a more substantial frame will almost always need more than the minimum air times listed below.

Rotation rates are obviously also affected by take-off mechanics. This means that a skater may jump higher than the minimum air time but lack the ability to create enough rotational energy on the take-off to spin fast enough in the air, even with a perfect air position and body type.

Coaches should strive to help their skaters optimize jump take-off technique and air position. Jump height is a result of jump technique as well, but overall skater athleticism appears to have a very strong influence on the ability to jump high. The development of athleticism is probably best attained through significant focus on off-ice training methods.

For more information about jump technique or off-ice training methods, please visit iCoachSkating.com. That website is committed to providing the best educational information on the nuts and bolts of how to figure skate.  It has literally hundreds of videos on jump technique from some of the world’s best coaches.

 

How to Measure Air Time

For accuracy, it’s important to maintain correct measurement methods. When analyzing jump air time, the measurement should be made from the first video frame a skater’s blade is in the air to the first frame the skater’s blade touches the ice.

It is NOT accurate to measure from the last frame on the ice to the first frame back on the ice. This measurement method will result in air time measurement that are too large. The details of this are beyond the scope of this article and will be provided elsewhere.

Simply use first-frame-off-the-ice to first-frame-on-the-ice and you’ll be fine. Most apps don’t have a way to reset the clock to zero on the first frame in the air, so record the time at the first frame in the air and the first frame back on the ice and subtract to get air time.

 

Shout Out to Christy Krall

At the 2011 PSA World Conference in Dallas, TX, World and Olympic figure skating coach and video analysis expert Christy Krall gave a presentation in which she provided insights about minimum air times for all the main jumps from double loop through triple lutz. To my knowledge, Christy has not published these findings elsewhere, partly since she uses these only as guidelines and there may be some skaters with successful jumps at lower air times.

I am publishing both Christy’s numbers and my own observations here for your reference. But remember, these numbers only represent our experience and are not absolute. Christy provided numbers for both male and female skaters (female/male). Air times are provided in seconds.

Jump                     Trevor                   Christy
Abbrev.               Air Time                Air Time

1A                           0.30

2S                           0.30

2T                           0.30

2Lo                         0.33                        0.35

2F                           0.35                        0.35

2Lz                          0.35                        0.35+/0.36

2A                           0.45                        0.45/0.47-0.51

3S                           0.47                        0.47/0.48-0.51

3T                           0.48                        0.47+/0.48-0.51

3Lo                         0.50                        0.51/0.52-0.53

3F                           0.53                        0.53+/0.56-0.58

3Lz                          0.53                        0.53+/0.56-0.58

3A                           0.60-0.62

4S                           0.63

4T                           0.63

 

These Minimums Are Not Absolute

Again, these numbers are not absolute. For example, I’ve seen 2 double axels with an air time of only 0.43 seconds. One was during practice sessions with a young skater in Korea with extremely efficient technique and a very thin body type and the other was off video taken by another coach of a similar Japanese skater who eventually became a World Champion. I do not consider 0.43 seconds to be a reasonable minimum air time for double axel because my experience shows that only an extremely rare and talented skater can pull it off.

Similarly, Sasha Cohen was capable of landing a quad salchow with just 0.60 seconds of air time. This astonishing feat of optimization may represent the absolute lowest possible air time for quad salchow, but most quad salchows are being landed with air times of 0.65 and higher. A significant number of skaters have landed the quad salchow at 0.63 seconds which is why it’s listed on the chart as the “reasonable” minimum.

When we use minimum air times with our skaters, we want them to target a reasonable number for their body type. So based on the skater’s body type and my experience, I may shift the numbers slightly so they have a more appropriate air time goal. We want skaters focused on meeting and exceeding air times that should provide success.

I hope this article is helpful. I did not ask Christy for permission to publish her air time numbers here but felt that her work deserves your awareness. Her groundbreaking research was a starting point for my own observations and this article would not be possible without her contributions.

 

Final Note

To get an idea of what these air times mean in regards to actual jump height, please see my previous post comparing air times with projectile height (Are Figure Skaters Projectiles?).  Sometimes it’s helpful for skaters to understand how much more jump height they need. Knowing that your double axel air time is 0.40 seconds and you need 0.45 seconds is somewhat abstract. But knowing you need to generate an additional 2 inches of jump height is very tangible to most skaters.

Please leave a comment and let me know if this article was beneficial.

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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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Double Axel’s Are Truly Rare

October 30, 2007

Lately I’ve been fascinated by the double axel.  This is probably pretty obvious if you’ve read many of my recent posts.  It is also obvious to the coaches that have signed up for updates from Skating Coach Quiz.

A large number of those coaches recently took a survey about the double axel.  The purpose of the survey was to determine how rare it is for a coach to teach a clean, consistent double axel.  I made the claim that “Most figure skating coaches never coach a skater to a consistent clean double axel.”

The survey results did not prove my claim, but they did provide food for thought.  60% of the responding coaches said they’ve never successfully taught a double axel to a female skater.  Of course, many of those will successfully teach a double axel at some time in the future.  But 60% is still a very sobering number!

71% of responding coaches worked with at least one female skater on double axel.  But only 40% have been successful teaching it.  These results confirm how rare it is to teach a double axel!  Some of the other survey results also suggest that most of the coaches that have successfully taught a double axel have been coaching for more than 20 years.

The other results of the survey were also very interesting.  The results can be viewed by signing up for updates from Skating Coach Quiz.  Those results include data on coaches’ experience levels and competitive success at the National level.

 

I’ve commented in this space before why so few ladies skaters get a double axel.  It largely comes down to physical ability.  Video analysis coaches with computer programs such as Dartfish have measured double axels with as little as 0.45 seconds of flight time.

 

Using projectile motion calculations, we can estimate the vertical jump from this flight time to be about 9.8 inches (see Flight Time versus Jump Height Table).  Actually the number is slightly greater due to ankle extension but 10 inches is a reasonable estimate of minimum height.  This assumes exceptional rotational speeds and jump control.

 

According to Audrey Weisiger and Chris Conte of Grassroots to Champions, the good minimum number for double axel flight time is 0.5 seconds which corresponds to a little over 12 inches of height.

 

Ultimately, that’s the challenge.  Most female skaters simply can’t jump that high off one leg.  Add to that the need for a proper axis and rotational control, and it’s clear why it’s so difficult.

 

I’m putting together a study of vertical jump height versus age for skaters.  The study will measure and correlate vertical jump height using multiple measurement methods, off one leg as well as both.  Ultimately, I’d like to correlate those measurements with on ice jump height as well.

 

I don’t really know what to expect.  What percentage of female skaters that skate for at least 3 years or more have the physical ability to do a double axel?  10%?  5%?  Even less?  It should be very interesting.

 

Trevor

 

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Are Figure Skaters Projectiles?

August 28, 2007

The title above is eye-catching on a number of levels.  Have you ever been on those high sessions with 25 skaters?

Actually, this post is a follow-up to my discussion of slo-motion versus computer analysis.  In that post I made the bold claim that the minimum height for a double axel is 60% higher than the minimum height for a double lutz.  In this post, I’ll show how I got those numbers.

Warning:  This post is extremely technical so if you just want the final answer, see the height and flight time tables below.

The work of figure skating video analysis experts has demonstrated that there is a minimum flight time requirement for each of the jumps.  For example, a double lutz needs to be in the air for 0.367 seconds or longer while a double axel needs to be in the air for 0.467 seconds or longer.  These values have been determined by analyzing hundreds of jumps with various video analysis programs such as Dartfish or Pro-Trainer.

Using the video analysis software, a coach can count the number of frames a skater is in the air.  You do this by advancing the jump entry and take-off frame-by-frame until the skate blade just leaves the ice.  You mark that as your starting point and advance the jump frame-by-frame through the flight until the skate blade just touches the ice.  The number of frames from the start to the end point give the flight time, as video cameras shoot frames at fixed time intervals.

In North America, the video standard is 29.97 frames per second but the magic of modern video analysis software such as Dartfish and Pro-Trainer allows those programs to double the number of pictures for certain consumer video cameras.  (In a future post I’ll discuss the technical details of interlace vs. progressive scan.)  That means we can resolve the jump flight time to 1/60th of a second (actually 1/59.94 of a second).

So here’s an example.  I’ve never analyzed a double axel with less than 28 frames of flight time at 60 frames per second.

28/60 = 0.467 seconds.  Dartfish and Pro-Trainer have timers so you don’t actually have to count the frames.

Now to calculate an estimate of how high the jump was, I apply the laws of physics.  In basic physics courses, there is almost always a part of the course devoted to “projectile motion” and the associated equations.  We’re going to consider our in-flight skaters as projectiles!  For our situation, the equation of interest is the simplified time-acceleration-distance equation. 

This equation states that the distance an object travels under constant acceleration from rest is one half the acceleration rate times the square of the time.  The equation looks like:  Distance = 1/2 x Acceleration x Time x Time.  For our skating jump analysis, we need to use half the total flight time as the Time in the equation as the skater at the peak of the jump has no vertical speed (“from rest” at the top of the jump to full speed at landing… to use the simplified equation).

The acceleration of a projectile is simply the pull of gravity.  And gravity has a constant acceleration of 386.088 inches/sec2.  Using the double axel minimum flight time of 0.467,  the decent-only time is 0.467/2 = .2335 seconds.  Plugging all of this into the equation yields:

Distance = 0.5 x 386.088 x .2335 x .2335 = 10.53 inches

Just for theoretical completeness, the actual jump height is slightly lower.  The reason is that a skater always points his or her toe at take-off but usually flexes the toe in the air and upon landing.  This makes the number of frames method a tiny bit inaccurate.  But the result is close to the theoretical.  A double axel must be 10.5 inches high or you can forget it.

(Some skaters land with their landing leg slightly bent.  Their jumps are actually slightly smaller than that indicated by the table below.)

Here’s the whole table:

Frames in Air

Flight Time in Seconds

Height in Inches

10

0.1667

1.3

11

0.1833

1.6

12

0.2000

1.9

13

0.2167

2.3

14

0.2333

2.6

15

0.2500

3.0

16

0.2667

3.4

17

0.2833

3.9

18

0.3000

4.3

19

0.3167

4.8

20

0.3333

5.4

21

0.3500

5.9

22

0.3667

6.5

23

0.3833

7.1

24

0.4000

7.7

25

0.4167

8.4

26

0.4333

9.1

27

0.4500

9.8

28

0.4667

10.5

29

0.4833

11.3

30

0.5000

12.1

31

0.5167

12.9

32

0.5333

13.7

33

0.5500

14.6

34

0.5667

15.5

35

0.5833

16.4

36

0.6000

17.4

37

0.6167

18.4

38

0.6333

19.4

39

0.6500

20.4

40

0.6667

21.4

It’s pretty fascinating to understand the ramifications of this table.  For example

  • A double lutz needs to be have a miminum flight time of about 0.36 seconds, so it will be 6.5 inches high. 
  • If a triple lutz needs to have a minimum flight time of 0.58 seconds (estimated), it will be 16.4 inches high.

OK…has that sunk in yet???  The triple lutz needs to be 250% higher than the double!!  WOW!  Do you see why so few skaters actually get all those triples?

I hope this was interesting and useful.  If you are enjoying this blog, please pass the URL along to your friends that may be interested.  Also, please leave a comment as I would love to hear from you.

Trevor

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Why Computer Analysis And Not Just Slo-Motion?

August 27, 2007

One 0f the main uses of video analysis software with figure skaters is determining flight times.  Why?  Because flight time or jump height largely determines jump success.  For example, based on all the video that I have analyzed, I have never seen a double axel that had less than 0.467 seconds of flight time.  And other video analysis experts have confirmed this value.

Dartfish experts Chris Conte and Audrey Weisiger use a value of 0.500 seconds for double axel.  But I have personally measured a handful of double axels at 0.467 and in fact, one of the skaters I work with regularly in Madison lands it consistently with that flight time.  But she is very slender and has an awesome rotation rate.  So most skaters that are not as slender will probably have to meet Chris and Audrey’s 0.500 second minimum.

If a skater is ready to work on double axel but cannot perform a single axel with at least 0.467 seconds of flight time, she should spend nearly 100% of her effort making her jump bigger.  The chances are simply not good that she will be the first skater ever to land a double axel with less than 0.467 seconds of flight time.

This feature of video analysis software truly sets computer jump analysis apart from basic slow-motion video analysis.  Of course, basic slo-motion has been used by coaches for years and is very common in figure skating.  But computer analysis provides flight time and takes coaching to another level.  Knowing the flight time of the jump is critical for understanding what is possible.

All the time, I see skaters that are attempting double axels and triples that simply do not have the height necessary to land those jumps.  And unfortunately, they continue to practice them over and over, teaching themselves to fall or teaching themselves to land cheated jumps.  Since their coaches don’t realize they will never land it without more height, they keep doing it, and ingraining an incorrect movement that can be nearly impossible to change.

And that largely explains why double axel separates the really good skaters from the rest.  At the recent Frank Carroll  workshop in Milwaukee, Mr. Carroll described skaters having jumps and jump combinations through double lutz as being very good… but skaters with a double axel are in another class.

And that’s also evident in some surveys I’ve done.  Many coaches rarely get the chance to work on double axel.  And when they do, they are almost never successful.  The percentage of ladies that actually learn to do it consistently is very small indeed.  And no wonder… just getting any female athlete to jump 10.5 inches off one leg is quite a feat! (10.5 inches represents 0.467 seconds of flight time based on projectile motion calculations… more about that in a future post!)

And here’s some more astonishing but useful numbers.  Minimum flight time for double lutz is about 0.366 seconds.  That makes the difference in flight time between double axel and double lutz just 0.1 seconds.  But guess what?  Those 0.1 seconds represents a whole 4 inches!!!  So you can do a double lutz with just 6.5 inches of height but you have to jump over 60% higher to land a double axel!  No wonder so many skaters never get one…

If you have skaters working on double axel, do yourself and them a favor by getting a computer analysis done.  Find someone to help you if you don’t have the tools yourself.  The bottom line is – computer video analysis is truly a major leap forward in figure skating coaching for advanced skaters. 

Trevor