Application of High Speed Video to Tennis Strokes - School

[Chas Tennis]

Want to use high speed video to observe something about a tennis stroke?

Post what you would like to observe.



#SEARCH_VIDEO_TENNIS_STROKES

 

[yossarian]

I would like to see high speed footage of the split step. Are high level players using a special technique in preparation for the ball? What specific joint moments and torques allow them to split step so smoothly

 

[PilotPete]

hi-speed video of all strokes that you can rotate around in 3D and view from all angles as some tennis broadcasts have done in the past.

 

[Chas Tennis]

Here is an interesting observation showing the value of high definition, high speed video with a fast shutter speed for minimal motion blur. Are Thiem's eyes open for his backhand impact?

Here is another technique for ball watching.

Watch his eyes on his one hand backhands.


I just looked at the slice and top spin one hand backhands and observed if his eyes were open or closed.

Eyes open for slice at 2:59, 6:12, 8:16 - total 3
Eyes closed for slice at 4:08, 4:41, 4:59, 5:41, 6:39, 7:02 - total 6

Eyes closed for TS at 0:31, 1:07, 2:17, 4:48, 5:30, 6:27, 8:07 - total 7
Eyes open for TS - none

That was surprising to me. Has this been observed elsewhere? link?

I noticed this on Almagro's serve also.

Doesn't this prove that ATP players do not have to watch the ball into impact on serves and one hand backhands....? (We already know that many ATP players turn their heads down and cannot see the serve impact.)

Alice saw some strange and interesting things after she went down the rabbit hole and had a look around.

 

[Chas Tennis]

Observe Thiem's forehand ball watching with this high frame rate, high definition, small motion blur video. Observe the eyes. Are they open around impact?

SEARCH_THIEM_BALL_WATCH

 

[MoxMonkey]

Its not about the tennis stroke itself, but I wonder what the speed/spin of a ball with heavy topspin is before the bounce and then after. Also how it's angle of attack to the ground impacts the bounce

I'd like to measure the kick

 

[Chas Tennis]

@MoxMonkey

A strong kick serve with a bounce to the right can be observed from behind the server.

But to see print or markings that you place on the ball, needs a close-up.

If the camera is located behind and near the net for protection, camera aligned with and under the ball trajectory, looking at the bounce, the print before and after the bounce should show and the bounce direction high and more to the right for a kick serve should show.

To see print on the ball at the bounce, it is easier with the camera looking along the trajectory vs the side view. That's because the motion blur is always smallest for the ball going away from the camera or coming toward it.

That should be a straight forward fun project if you have a strong kick serve available and high speed video camera with a fast shutter speed.

If the ball bounces high, but not to the right, I'd suspect that is a top spin serve, but not a kick serve. To get the kick to bounce to the right, see videos of Stosur's & Federer's kick serves. The racket face has to be closed about 13-15 degrees just before impact.
Search thread - Junior Twist Serve

Federer & Stosur videos with racket closed tilt.

Needed - Strong Kick Server for Video Measurements.

For the kick serve there are many disagreements in the forum posts that could be resolved easily if a few videos were taken. What is needed is a strong kick serve that bounces clearly to the right and a 240 fps camera with a fast shutter - many smartphones will do - and small motion blur...

tt.tennis-warehouse.com

Video in bright direct sunlight and your camera's automatic exposure control will select a faster shutter speed and reduce motion blur.

For best results get a high speed video camera, 240 fps is good, that has manual exposure control. New manual exposure cameras are very hard to find as almost all are now automatic. Last year, I purchased two old used Casio FH100 cameras in excellent condition for $115 and $85. Casio models F-1, FH20, FH25 and FH100 have very fast shutters down to 25 microseconds (1/40,000 sec). For a close-up of the ball from the side, there will be Jello Effect distortions and motion blur. But looking along the ball's trajectory, there is not much relative motion, so not much Jello Effect or motion blur. The Jello Effect for these cameras is very small, negligible, for motions of the serve.

Let me know what model camera you have and I will try to find something on the motion blur. I usually search for Youtubes with motion blur on golf swings in bright sunlight.

Google
Physics of the Kick Serve, Rod Cross, a link on this forum. Cross has published on the kick serve and how to mark the ball for spin measurements.

I believe that I read from Cross that the spin axis on a serve remains in the same direction as the ball travels from impact to the bounce. The ball acts like a gyroscope. But gravity and air forces from spin will change the ball's trajectory. If you define spin direction relative to the changing trajectory, as for 'side spin' or 'gyrospin', etc. note that.

Measuring rpms on strokes

How does one measure the amount of spin that is put on a shot?

tt.tennis-warehouse.com

To understand why the ball bounces to the right, see posts with ball held in a drill, read thread Junior Twist Serve. (I believe that the picture is no longer available.)

https://tt.tennis-warehouse.com/index.php?threads/junior-twist-serve.643500/

 

[Chas Tennis]

hi-speed video of all strokes that you can rotate around in 3D and view from all angles as some tennis broadcasts have done in the past.

I think those 3D views are probably done with an array of many video cameras. I don't know much about those set ups.

 

[Chas Tennis]

I would like to see high speed footage of the split step. Are high level players using a special technique in preparation for the ball? What specific joint moments and torques allow them to split step so smoothly

The idea of the split step is to have stretched leg muscles, hip muscles, ankle muscles and others? and be able to move to the right or left just after you see the ball struck. In other words, you are timing stretch shorten cycles for many muscles.

Taking videos. An interesting thing to observe is the timing between the player striking the ball and the player doing the split step. This timing would be learned or taught. Video shows you the timing.

1) With camera mostly behind the player spilt stepping, frame the video so that both the player split stepping and the player striking the ball can be seen. This is an easy set up, but the split step viewed from behind is probably not the best view of the split step.

2) If you want a side camera view of the split step player, a small mirror may be held in front of the camera so that the split step player is directly viewed and the small mirror - to one side - shows the striking player. Ask about suggestions for mounting.

3) Two cameras can be used with one camera on each player. But then some way must be found to time one video to the other. Kinovea can take two videos and make a side-by-side video.

Finding pro videos. (You have no control of the video recording.) You should also be able to find pro videos where both players can be seen and do statistics on the split steps' timing. At 30 fps or 60 fps you should get a good idea of the timing of the split step vs the struck ball that is in use in the ATP and WTA.

I believe that players use the knees, hip joints and ankles to 'unweight' then land on the ground to stretch knee extender muscles, hip extender muscles and ankle plantar flexion muscles...? There may be other joint motions involved, see high speed videos of pros.

 

[Chas Tennis]

hi-speed video of all strokes that you can rotate around in 3D and view from all angles as some tennis broadcasts have done in the past.

Is this what you meant?

Place cursor in video, click to select and hold and move it around. I can use the touch screen on my laptop to expand an area of the video.

Looking directly down shows a Giroptic 360 cam camera. (cursor up)

 

[Chas Tennis]

I would like to see high speed footage of the split step. Are high level players using a special technique in preparation for the ball? What specific joint moments and torques allow them to split step so smoothly

The emphasis of this thread is on video techniques to get the stroke information that you are after. If I happen to find something as an example, I'll usually show it.

This example shows Schwartzman spilt stepping and his opponent striking the ball. The video technique/camera angle is excellent in that it includes the opposing player and records the timing of Schwartzman's split step. Protect the camera from getting hit by the ball, outside the fence is one option. This video was also recorded in direct sunlight and the shadows may be useful for observing specific muscle motions. Shirtless always gets forum comments, but the activity of some body muscles might be shown that otherwise could not be observed through a shirt.

The split step times stretch shorten cycles of leg muscles, and maybe some others, to the player's early observation of the ball's trajectory.

Discussion of the split step and its timing to the opponent's stroke starts at 28 seconds and ends around 1:15. This video starts at 28 sec.

 

[Chas Tennis]

The Under Impact Camera

The overhead camera view of tennis strokes is rare because it requires supporting the camera above the server. Cherry pickers, booms, or drones may be used. Beware any safety issues. Some drones may drop under some circumstances.

To get around these problems I set up and tested an under impact camera and took a few videos of forehands at 240 fps (Casio FH100). This video has pauses. Also single frame on Youtube using the period & comma keys.

This camera was placed under the forehand on a towel and a ball machine was used. The camera was protected from the ball with my tennis bag. Avoid having the sun in the frame of the camera.

link

Vic Braden may have used a similar camera location.?

 

[Chas Tennis]

Comparing two videos one above the other and single frame on the forum.

Alt-left mouse click also works to single frame on two videos on the same forum post. This places the two videos close, best for comparisons.

Compare any two forehand clips.
1) Go to video and stop near a forehand impact.
2) Place the cursor on the video - always well away from the time line - and hold the Alt KEY down and click the LEFT MOUSE BUTTON to select that video.
3) On Youtube use the PERIOD/COMMA KEYS to advance or go back one frame. Find frame closest to impact.
4) Go to second video and repeat above steps selecting another forehand impact.
5) Move across frames to compare videos always using Alt-Left Mouse Click to select the video that you want to work on.

This is working on my computer with Windows 10 and Chrome. I am using the laptop touchpad. There were no unintended starts of the video playback when using Alt + Left Mouse Click.

Compare any two forehands.

Could some readers please try this and post back any issues.

What needs to be made clearer in the instructions?

..........
Comparing Youtube & Vimeo Videos Side-by-Side and Single Frame.

For Vimeo
1) Select a forehand and stop on the impact frame.
1) For single frame in Vimeo, selecting the video does not automatically start it playing. No problem.
2) To single frame on Vimeo hold down the SHIFT KEY and use the ARROW KEYS.

For Youtube
Compare any two forehand clips.
1) Go to video and stop near a forehand impact for comparison.
2) Place the cursor on the video - always well away from the time line - and hold the Alt KEY down and click the LEFT MOUSE BUTTON to select that video.
3) On Youtube use the PERIOD/COMMA KEYS to advance or go back one frame. Find frame closest to impact.
5) Always use the Alt-Left Mouse Click to select the Youtube video that you want to work on so that it will not start playing.