thanks todd
does the plane of the shoulder turn necessitate a particular posture or orientation of the spine?
Pelz thinks that the shoulders can move vertically quite happily. Others have criticised this as an unnatural movement, or at least one that is difficult to learn.
I think the stroke that Utley teaches has more arm movement than shoulder movement - partly because the arms swing "in-plane" whilst the shoulders rotate flatter, with the result that the elbows need to fold and extend in turn, back and through.
How do you measure the motion of the shoulders in-plane?
To execute a "shoulder-only" stroke, put a club under your armpits to "lock" the arms down. They are now "fused" in place. Now execute a an in-plane stroke, monitored by laser, plane board, etc. I actually find it easier to keep the upper sternum fixed when turning the shoulders parallel to the stroke plane, which is much closer to vertical than is a plane perpendicular to the spine. Sort of like Stack N Tilt.
As the arms swing independently from the sockets, with both hands on the club, one arm must be folding in at all times. Stan has described this well. Almost always, the stroke is powered by a combo of both shoulder rotation and arm swing.
Here's a video I did a while back, in the early stages of organizing this pattern, which shows the in-plane shoulder-only stroke