1 Topic by Chas Tennis (edited by Chas Tennis 2025-08-29 22:40:17)

  • Chas Tennis
  • Member
  • Offline

Athletic motions can be divided into sub-motions that are useful for understanding and communication.

When viewing athletic motions, single frame advance is often used.  A problem with single frame advance is that the frames before  and after the viewed frame have to be remembered.  Things are missed.

The Forth & Back Video Display Technique is another approach that I think can work better if the viewer can control displaying the video.  I have found that some things are easier to notice and study using Forth & Back displaying. Spatial & temporal information are noticed better.  I study sub-motions with it.  A sub-motion is anything that is useful for understanding.

On forums it works smoothly with Vimeo videos.   A Kinovea video with a millisecond count down time scale is perfect for the fastest  athletic motions. 

Kinovea Analysis of a Kick Serve. Recorded at 240 fps. Use Forth & Back on it.
https://vimeo.com/196108282
Go full screen, start video then stop video, now drag the white time indicator Forth & Back, Forth & Back.....to display sub-motions of the tennis serve.  You can move the cursor up, out of the way, and it still controls the frame time displayed.

With the Kinovea millisecond count down timer, time lines for all joint motions, sub-motions, ball impacts, etc., can be observed and estimated from a single high speed video.

Could Forth & Back also be added as a capability of Kinovea for split screen display with millisecond time scale?

2 Reply by joan

  • joan
  • joan
  • Admin
  • Offline

Hi Chas, yes I love this interaction mode, I use it all the time. I'm not 100% sure we are talking about the same thing though because this should work pretty much the same in Kinovea already. If you grab the navigation cursor and move it back and forth it should update the image immediately. The smoothness depends on whether the images are cached in memory, if they are not it depends on the video encoding.

There is another interaction mode called "time grab", you hold ALT key you can then grab anywhere in the video viewport with the mouse and move left/right to go back and forth in time.

3 Reply by Chas Tennis (edited by Chas Tennis 2025-09-02 22:38:36)

  • Chas Tennis
  • Member
  • Offline

I had practiced the serve for 35 years, but I did not know the correct main sub-motion.  Even the tennis research world did not know of the correct sub-motion - Internal Shoulder Rotation - until 1995!  (Elliott & Marshall publications). Now, 30 years later, most active tennis players still do not understand. I refer to this situation as the Tennis Serve Nuthouse.

On Talk Tennis forum, I have posted on tennis strokes and their sub-motions for years.  Still, it's a battle to get more posters to view high speed videos and observe things.

A thread on Talk Tennis forum, The Tennis Serve - What's True?
 The latest posts are on Forth & Back. 

In the past, if I suggested any video analysis, there were only a few serious readers that did it.  Most posters do YouTube single frame now, I guess.

I notice sub-motions better doing Forth & Back on Vimeo videos and I recall better what I have seen. Using only a one sentence instruction, anyone can be doing Forth & Back on Vimeo videos in a minute.  However, the available tennis stroke videos from Vimeo are limited. Mostly, I have found videos from my collection.

My goal is to find a very easy way for people to view the sub-motions of tennis strokes, with hardly any learning curve and aimed at a new crowd. The Vimeo videos for Forth &  Back have been very short videos of single tennis strokes. Longer videos may cause problems with dragging the time indicator. ?   

I thought of what Kinovea can do, so I posted on this forum. 

Also, there is a subject, new to me, that seems likely related to the serve, Spinal Engine Theory.  Coco Gauff's new serve coach, Gavin MacMillan, advocates Spinal Engine Theory for the tennis serve. Spinal Engine, unlike joint motions that bend more, does not show well in high speed videos because the spine bends are small and the players wear shirts.  Some next level observation techniques, Forth & Back or "time grab" or better, might help show Spinal Engine on shirtless servers.  Information on Spinal Engine is also in the tennis serve thread.