[Jeff]

I agree that LB explained it very well in that Barclay's Academy video.

As a TGMer who is very interested in golf biomechanics, I will add just one point - that the different degrees of hinging are primarily due to variable degrees of external rotation of the left humerus at the left shoulder socket joint per unit time during the followthrough, with horizontal hinging having the greatest amount of external humeral rotation per unit time. The left humerus rotates at the same rpm as the left forearm which rotates at the same rpm as the FLW which rotates at the same rpm as the clubshaft.

The second point is that this external humeral rotation happens naturally in response to the golfer's intent - the intent to control the clubface via the left hand.

It is not an "unnatural action" that requires practice, as argued by Tom Betrand in his swing video on the "missing link" in Hogan's secret - the missing link of "actively turning-in the left elbow towards the left hip".

Jeff.