[Jeff]

I have still not received an informative opinion that explains the biomechanical difference between a finish swivel action and horizontal hinging - with respect to the movement of the left hand.

Consider this particular problem from this angle.

Here is photo of Kevin Na's clubhead path through the impact zone.



One can see that his splined clubhead path demonstrates that he is swinging his clubshaft on the inclined plane and that he is tracing the base of the plane line post-impact. At the same time, his clubface has rotated counterclockwise while the clubshaft is travelling on the inclined plane - and this represents his horizontal hinging action. HK states that it occurs due to rotary forces operating at left shoulder level, and one can imagine that there is a hinge joint horizontally oriented at the level of the left shoulder - as demonstrated in this TGM photo.



The effect of this hinge action is that the back of the left hand supinates slightly while it is moving up the inclined plane. Supination is a rotary motion, which means that the left hand is rotating during this horizontal hinge action phenomenon. Tiger Woods describes this "feeling" as the feeling of turning the knuckles of the left hand towards the ground after impact. He is therefore aware of a rotation of the left hand. That left hand rotation (supination) is no different to the more complete rotation (supination) that occurs fractionally later in time (during the finish swivel) as the left hand supinates more fully so that the back of the left hand lies against the inclined plane. The only difference is that the first left hand rotation (during the followthrough) primarily occurs due a rotation of the left shoulder socket left-backwards (as part of the torso pivoting action) + rotation of the left arm/forearm unit at the left shoulder socket level, while the second left hand rotation (during the finish swivel) primarily occurs due to left elbow folding and left forearm fanning combined with an active pronation of the right forearm. Although the biomechanical driving mechanisms are different, surely the left hand is rotating (supinating) throughout the followthrough and finish phases of the swing, and it is really a continuous rotary movement.

Jeff.