In another thread, Yoda stated that a golfer needs a i) pivot center and that the pivot center needs to be centralised between the feet.
Of all HKs' ideas I have never understood why there needs to be a pivot center for the swinging arms/clubshaft.
I can understand a grandfather clock having a pivot center located at the fulcrum of the pendulum because i) the length/radius of the pendulum arm is constant and ii) the low point of the pendular arc is constant.
However, golfers don't have a consistent ball position and/or a consistent low point - relative to the center of their stance. Also, the length (radius) of the left arm/clubshaft swinging structure varies continuously during the downswing. Also, the fulcrum (left shoulder socket) of the left arm/clubshaft structure moves in space continuously and has a variable distance from the required low point (a set number of inches ahead of the ball). Also, although the low point of the swing is roughly opposite the left shoulder socket area, the left arm/clubshaft length/radius is not necessarily at its greatest value at that time point. The left arm/clubshaft's length/radius is at its greatest value when the left arm is maximally straight and the clubshaft is maximally straight-in-line with the left arm, and that occurs at the end of the followthrough.
Maybe that is why HK didn't state that a stationary head is an imperative, but more imprecisely classified it as an essential requirement. Rhythm and balance are also imprecise concepts that are classified as essential requirements.
To make any further discussion interesting/informative, I am including a series of photos showing the pivot center of different golfers. I drew red lines through the pivot center (defined as a point midway between the shoulders) at address. I then left the red line constant, and captured two additional images - at the end-backswing and at impact.
From this swing video -
Gary Player
Arnold Palmer
Jack Nicklaus
Mike Souchak
Here is another swing video that is pertinent to this discussion
From this Natalie Gulbis/Paula Creamer swing video -
Natalie Gulbis
Paula Creamer
If I were considering essential requirements (and not imperatives) for a golf swing, I would consider removing "stationary head" and inserting "set distance of the left shoulder socket from the ball at impact".
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