PDA

View Full Version : JohnYandell , AndyFitzell ,Tennismastery ,JCo872 Other Video experts.


Mike Cottrill
08-29-2006, 09:29 AM
JohnYandell (http://tt.tennis-warehouse.com/member.php?u=7267) vbmenu_register("postmenu_1102554", true); , AndyFitzell (http://tt.tennis-warehouse.com/member.php?u=25121) vbmenu_register("postmenu_1100757", true); ,Tennismastery (http://tt.tennis-warehouse.com/member.php?u=12393) vbmenu_register("postmenu_1101359", true); ,JCo872 (http://tt.tennis-warehouse.com/member.php?u=8363) vbmenu_register("postmenu_960730", true); Other Video experts.

This post is in reference to John’s interest in 3D data. My question is similar but related to 30 fps video versus high speed video like 240 fps. As a layman, I would like to know what you see from high speed video that you can not see from 30fps. What key mechanic flaws or inefficiencies appear? Willing to participate?

Thanks
Mike

MasterTS
08-29-2006, 09:43 AM
In layman's terms.. What the hell are you talking about!!!!

JohnYandell
08-29-2006, 10:43 AM
Mike,

You can see a lot in 30 frames. The general shape of the strokes, the unit turn and full turn, the size and general shape of the backswings, the footwork, the path of the followthrough and the wrap, the recovery steps.

The problem is trying to see what happens around the contact, and the shape of the hitting arm on the forward swing as it moves into the contact.

These are some of the most disputed points in teaching. You have some coaches on the internet who use a lot of video in their analyzes, (not you BB, not you...) but have based their conclusions only on 30 frame video and have misinterpreted things because of it, in my opinion.

A few examples on the forehand: the racket face for some players is somewhat or even completely closed toward the bottom of the backswing. But it changes with the creation of the hitting arm structure in the the split seconds as the racket starts to accelerate forward. It's always on edge to a certain degree, depending on grip, as it starts forward. But a lot of players have screwed up their forehands keeping the face closed too long.

The issue of the wrist is another. It always starts laid back. At some point after contact it ususally releases fully and goes to a netural position or sometimes a little further. When this happens though depends on where the player is on the court, the angle and height of the incoming shot, where the player is going with the shot, and with how much pace or spin--and also on the grip. A lot of factors.

But with 30 frame video you usually see a frame somewhere before and a frame somewhere after contact. But not multiple frames around the contact or the contact itself. You catch the ball on the strings 1 of 10 times, and when you do you lack the immediate frames before and after. You can reach the wrong conclusions extrapolating from this limited information.

That's one thing that is great about Jeff's hi-tech video--he has separated out the fields and gets 60 frames and always looks for examples where he actually has the contact point.

With 250 frame video you have even more: the contact and a lot more info just before and after. You often see the wrist laying back even further as a result of the impact at contact and not releasing til further out in the stroke. Or not. It's complex but the video demonstrates pretty conclusively that the wrist doesn't independently snap forward with conscious muscle contraction. Yet a lot of people still fervently believe that it does.

Same issues on the hand and arm and writst motion on the serve. That's been debated here before, so I won't dredge that one up again right now.

3D is the next frontier because it adds actual measurements to the high speed pictures and this has the potential to make the descriptions even more accurate. As I've said it's so complex that I think the final arbitration will always be opinion to some extent but the prospect is exciting. The problem is it is very difficult and expensive to film, and extremely time comsuming and complex to analyze.

John Yandell

JCo872
08-29-2006, 11:05 AM
I'll just offer one addition to what John said. I sometimes get a better sense of the "rhythm" of things with the 30fps video. Once you get into 60fps and higher, things become too slow to get an overall feel of the rhythm (when they are accelerating and when the are holding back). The high frame rates are invaluabe, however, for seeing what is (and isn't) happening right around the contact point, as well as other details. This becomes ridiculously true with the "tornado cam" where you can see how the ball and strings actually merge and interact with each other.

I still love the 30fps video and have started to use it in addition to the 60fps clips I have on my site. I think it is most helpful to use all the different frame rates. As John said, you can get into huge trouble only studying the 30fps video. Your brain can impose additional motion (pronation or wrist snap on the forehand during contact) onto the video that just isn't happening as the ball is on the racket strings. The shot happens very quickly, so separating cause and effect becomes easier with the high frame rates.

JohnYandell
08-29-2006, 01:15 PM
Have to agree about the rhythm thing. Looking at every speed has it's benefits.

Bungalo Bill
08-29-2006, 02:06 PM
I'll just offer one addition to what John said. I sometimes get a better sense of the "rhythm" of things with the 30fps video. Once you get into 60fps and higher, things become too slow to get an overall feel of the rhythm (when they are accelerating and when the are holding back). The high frame rates are invaluabe, however, for seeing what is (and isn't) happening right around the contact point, as well as other details. This becomes ridiculously true with the "tornado cam" where you can see how the ball and strings actually merge and interact with each other.

I still love the 30fps video and have started to use it in addition to the 60fps clips I have on my site. I think it is most helpful to use all the different frame rates. As John said, you can get into huge trouble only studying the 30fps video. Your brain can impose additional motion (pronation or wrist snap on the forehand during contact) onto the video that just isn't happening as the ball is on the racket strings. The shot happens very quickly, so separating cause and effect becomes easier with the high frame rates.

I like to use 60fps for segment analysis. To prove out things that are misunderstood, unseen, dismissed, taken for granted, or simply need to be analyzed more to incorporate into instructional methods.

I like to use 30fps to view the entire stroke for fluidity, the kinetic chain, and the overall summation of the stroke from preparation to followthrough while having an eye on the segment being studied. Also at times, I will step through a 30fps segment to analyze major components that contribute to stroke performance.