1) Lumbar Lateral Flexion.
One of the main body orientations to achieve the shoulder orientation is
lumbar lateral flexion
- this is a side-bending of the spine and I believe is often spoken of as a 'trunk side bend'.
2) Scapular Repositioning?
The scapula also might be repositioning to some degree to minimize impingement. ?? See last seconds of the video viewing from the back and showing the scapular motion. There would not be much scaplular elevation
or it would conflict, I guess, with the advice in the Ellenbecker video. ?
3) What Part is Played in the Serve.?
An interesting discussion from the Manual of Structural Kinesiology
indicates that -
The lat & teres major are stretched when the shoulder is externally rotated while in a 90° abducted state (90° of shoulder abduction is the approximate orientation when the leg thrust occurs). The reference discusses how the shoulder may be farther stretched by laterally flexing
and rotating the trunk.
CF, This elevate-the-shoulder motion might follow the 'chest up' that you have pointed out in some replies as important for a strong serve?
This last observation indicates that the lateral flexing may not only be for avoiding shoulder impingement but also to play an important part in the service motion.