Linthorne provides a fairly thorough mathematical anaysis on the factors and formulae that cover this topic. The main issue I have with his paper is that he arbitrarily adds 1.00m to his calculations to cover the "average pushoff" of an elite vaulter. Clearly, the pushoff varies significantly from one vaulter to another. And clearly, the EFFICIENCY of each vaulter is hidden somewhere in their pushoff.
One objective that I propose of this video analysis methodology is to try to nail down additional factors that can "rationalize" or "explain" why one elite vaulter's pushoff might be more or less than another's. I'm quite certain that the speed of the DOWNSWING ... once measured ... will become a VERY important consideration in determining a vaulter's pushoff or efficiency. But there's others.
Another objective is to be able to scale this video analysis back down to your own vault, or to the vaulters that you're coaching. My hypothesis is that we will find a continuum of metrics from beginners thru intermediates and elites ... male and female. If you're "off the scale", then you're either doing something terribly wrong ... or terribly right!
A further objective could be to scale it down to elite women vaulters, to try to identify (more precisely) in which part of their vault women are relatively slower or weaker then men.
Another is to take videos of your subject vaulters at various times during a season ... or from season to season ... and compare their progress over time ... using these common data points.
Yet another idea is to standardize the metrics captured from vids, so that we can communicate with a common language ... including common data points taken from vids at key points.
I'm sure there will be other good things that will materialize out of this idea.
Some of this work is already done. I'll have to dig back on my notes from 4 years ago, but that's when I was helping Pat Licari analyze vids of Brad Walker, and I manually took some of these specific data points during his vault and attempted to compare them to other elites. That idea really never got off the drawing board and into "production" but today ... it's better late than never.
In communicating with DJ about that idea, I heard from him that he had done a lot of earlier work dating back to the 1980s with Mike Tully, timing and measuring his vault parts. He has mentioned many times on PVP the importance of the timing of each vault part, and the fact that an elite vaulter takes about the same amount of time "in the air" as a college or HS vaulter.
I owe a lot of credit to DJ for helping me to formulate my ideas about these Video Metrics.
He did much of the original work, and I followed his footsteps. I haven't talked to him about this yet, but I'm also hopeful that he will contribute to this thread in a significant way ... his time and interest permitting.
The idea is actually very simple ...
1. Videotape the vaulter, or use readily available vids of vaulters found on the internet.
2. Take video frame samples of a vault.
3. Take data point samples (by both time and distance) of the vault at key body positions.
4. Compare these data points to other vaults.
The points that I propose (which we can discuss and decide upon where my ideas are suboptimal) are:
1. The frame just before the takeoff foot leaves the ground (compared to the frame just before that).
2. The frame just before the pole hits the box (compared to the frame just before that).
3. The frame just before the "I" (Whip) position at the end of the downswing (compared to the frame just before that).
4. The frame closest to the "flat back" position (compared to the frame just before that).
5. The frame just before the top hand releases the pole (compared to the frame just before that).
6. The frame closest to max hip height (compared to the frame just before the top hand releases the pole).
Why these 6? Well, (1) gives you the runway speed; (2) gives you the "jumping impulse" speed; (3) gives you the "downswing" (max trail leg swing) speed; (4) gives you the "upswing" speed; (5) gives you the extension speed; and (6) gives you the speed of vertical deceleration from pole release to bar clearance. Unlike the others, this deceleration speed isn't anything that you can do anything about ... you're at the mercy of gravity then. It's simply a RESULTANT metric, caused by the other metrics measured by 1-5.
So what do we want to measure on these sample frames?
Speed = Distance / Time
If we can capture time and distance, we can determine speed.
And if we know the speed of each of these 5 key vault parts, we can compare them, analyze them, make decisions on if they're too fast or too slow, and ultimately use them as a guide for focussed training to improve specific vault parts.
To say this another way, we already know that the faster we're running just before takeoff, the higher we can vault (all else being equal). This idea takes it a step further, to see which vault parts AFTER the run are too slow.
Once we identify them, we can fix them! If you don't know what's broken, you can't fix it!
The TIME is computed from the camera shutter speed.
The DISTANCE is measured by laying the target frame over the frame just before it. The distance between the "key body point" on the 2 frames, multiplied by the scaling factor of the frame, gives the actual distance in meters and fractions of meters.
What are the "key body points"? They vary per frame. You want to pick body points that are easy to identify, and represent what you're measuring.
The CoM is an important body point, but it will vary according to your various body positions during a vault. A good approximation of the CoM is the point at which a vaulter's shorts intersect with his jersey, just below his belly button (as opposed to his back side). Especially with contrasting colored shorts and jersey, this is usually an easy point to identify.
A better idea ... if you think of it before videotaping ... is to mark a dot (visible on vid frames) on the side of a vaulter's shorts or jersey in a contrasting color. While you're at it, you could mark dots on certain fulcrum points of the body, such as the shoulder, hip, knee, and ankle ... but that's more than we need for my basic idea of capturing common data points (so pardon the digression
).For (1) and (2), take the shorts/jersey intersect point; for (3) take the intersect where the trail leg ankle intersects the heel of the track shoe; and for (4) (5) and (6) take the shorts/jersey position.
So now we have times and distances. Now we need to SCALE the distances. Here's how ...
This is Pogo's post today on the "Push off" thread, that partially inspired me to get this post started (although I've been planning to do this for a few days now) ...
Pogo Stick wrote: I think grip data are more accurate than any other data (except bar clearance
2" error is 1% of pole length (very accurate) or 5% of push off value (acceptable). ...
If you know a vaulters standing height ... which is usually well publicized ... and you have vid of the vault ... you can determine his grip ...
1. Find the frame where he's finishing his downswing, and his trail leg is aligned with his torso and top arm (the "I" position). Alternately, you can use the frame just before takeoff, as long as his takeoff leg is directly under his torso.
2. Measure his height on that frame ... from heel to top of head. Adjust for any abnormal head or ankle positions (if any).
3. Find a frame during his run or plant where the entire pole is visible ... and straight.
4. Measure his pole length, scaling by his known height and his height in the vid frame. Since poles are manufactured in common lengths, you can verify the accuracies of your 2 measurements thus far, and adjust accordingly (assuming his pole isn't cut to a custom, unknown length).
5. Using the same (verified) scale, measure the distance from the top of this known pole length to his top hand, and subtract that from the pole length. That's his grip!
There will be some inaccuracies in this method. If you simply measure directly on a computer screen, your "pencil point" will be quite large relative to the distances you're measuring. If you don't have any high-tech measuring devices to measure the images directly, you can mitigate this by printing the frame(s), and then enlarging them on a photocopier. All data points will be enlarged to the same proportions, so using low-tech measuring tools (pencil, ruler) on the enlargements will be more accurate.
Since you're wearing the engineering hat Pogo (and have lots of time on your hands
), I leave it to you to determine how accurate this measuring method is.OK, now we have time, distance, and scale!
So now we can measure REAL distances from vaulting vids! ... and get REAL speeds of vault parts to compare ... and figure out what factors (speed, distance, timing) of vault parts AFTER TAKEOFF affect a vaulter's pushoff. THEN, we can truly measure which vaulters ... short, tall, light, heavy ... have advantages over each other in specific vault parts ... with the ultimate objective of determining which techniques we should emulate, how we should emulate them, and why.
Along the way, we should be able to mathematically compare disparate models, such as Joe Dial's "drive vault model, to Bubka's "Petrov model".
One last question ... should we compare SPEEDS, or DISTANCES?
We could do either, but distances will need to be scaled quite a bit if we're comparing a HS vaulter to an elite ... and you can't just compare the distance between 2 frames - you need to compare distances between one vault part and the next (separated by frames 1-5). Since DJ has already determined that the time "in the air" is similar for ALL levels of vaulters, comparing SPEEDS might be more straight-forward. Really, just comparing SPEEDS keeps things very, very simple!
You can also compare the SPEED DELTAS between one vault part and the next (by counting frames). This gives you the ACCELERATION or DECELERATION of the body during that vault part. Pogo can give us the formula for that! But to do that, we need one more metric - the speed of the CoM (approximated by the shorts/jersey intersect) at the end of the downswing (Frame #3). We can't compare trail leg swing speed to "torso" speed ... that's comparing apples to oranges.
Will this idea work? I dunno! We'll have to put it into practice! So far this is just a theory!
Pogo and DJ ... can you help me with this? Carolina? Tim? Anyone else interested in this?
Kirk
