Posted by: tom.guerry (tom.guerry@kp.org) on Fri Dec 7 11:37:53 2007

Jack -

Thanks for sticking with this.

The way I think of it is that the shoulders "rotate" from "bathead launch" to contact.

Bathead launch is hard to pin down, but "mechanically" speaking would be when the center of mass of the bathead gets outside the arc of the handpath to trigger the self amplifying transer of momentum to angularly accelerate the bathead.

This is often very slightly before what is traditionally described as the "lag position" which is when the bat is pointing straight back to the catcher.

At this point, the bend is still in the back elbow and the hands are still with the back shoulder.

prior to this the back shoulder and hands HAVE turned forward some some BUT the hips have opened faster so there is no unloading/reversal of torso coil yet (so I would not consider this "shoulder rotation"). This would be more like the part of the swing you call "launch" or "THT at launch" or what can also be described as "drop and tilt".

Prior to this, the hands and shoulders stay back as the lower body opens and the bat is accelerating back to the catcher. You would call this "pre-launch THT.

So the point/distinction that I am trying to make is that the primary shoulder action during THT at launch (or Drop and tilt) is a TILT of the shoulders to accentuate THT and to provide a resistance, EVEN though the hands and shoulders are starting to turn forward as the hips continue firing open. This "resistance" creates a late/distal "control point" for adjusting swing plane and timing.

Again, it is necessary to break things down into the mechanical and the biomechanical domains at some point in analysis.

The "biomechanical"/"ruberbandeffect" makes the more purely mechanical effect very complex to analyze.

I think the Zig measurments are a good window into the mlb swing rubberbband aspects. You need the stretch and fire/x-factor stretch of the torso to produce the "early batspeed" which is measured as "efficient speed gains" of each arc with the final arc (bathead) able to start acceleration well back in the swing plane for deep contact.