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Re: Re: Re: Axis Tilt & Shoulder Rotation


Posted by: tom.guerry (tom.guerry@kp.org) on Wed Jan 23 20:42:18 2008


Jack-

As I detailed in a post (?lost in moderation process?) under the Jack Mankin thread below,
I would say the main thing that rotates is the torso around the spine. The TORSO has a
"spinal axis" and is what rotates. This is what Ray Porco has called "spinal rotation to
distinguish this from "shoulder rotation".


Think of the upper spine as the axis and the collarbones/sternum/ribs/spine as what does
the rotating.

The "shoulders" are best thought of in terms of SCAP action which is primarily a tilting
action to control load and unload. Similar to what you might think of as a shrug.

The shoulders/scaps tilt and lock on to the torso and in doing so, resist turning which is
working up from the hips so that the load/coil of the torso ends with a quick stretch. X-
factor/separation maxes out with a last (control point for direction and timing of load)
quick stretch/"x-factor stretch".

So the CHP and torque model is more like ball on string with upper spine as axis and
ability to control swing trajectory by handle torque which not only fires bathead out, but in
doing so develops resistance to control last bit of coil so reversal/unloading is well
synched/timed/sequenced.

The CHP/ball on string/string tension is not violated as long as the lead elbow does not
get away from the spine and as long as the extension/unloading sequence is such that the
uncocking of the wrists is well underway before any unhinging/extension at the lead
elbow occurs (there may be no opening of the lead elbow angle before contact on middle
in and some opening before contact for outside/high load situation).

For in to very in, the radius to the front elbow can shrink by pinching of the lead scap to
move the center of rotation from the spine to the front shoulder.

As you said, Adair probably did not understand how "ball on string" needed to be
modified based on the opportunity for applying handle torque as the main controller of
swing trajectory. HE was probably thinking in terms of grip having no effect on collision as
opposed to understanding that handle torque is crucial in bat acceleration/trajectory/
getting the bathead to contact quickly with early batspeed and with late plane adjustment
for generous contact zone.

Your handle torque and ball on string type model is better than "double pendulum" in
explaining the swing, although I would say it's more the arc of the lead elbow (with
respect to center of rotation of uncoiling upper torso) that must have a circular or
tightening arc which can be adjusted by either front scap pinch (inside) or moving of the
position of the head/upper spine (outside/high load).


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