This is the transition from the end of the back swing to the down swing, where during the back swing movement the left shoulder was in overal control, however from this moment onwards the control of the upper body unit is passed to the right shoulder.. ( highlighted in red)
My only thoughts are concentrated on keeping the right shoulder in total control of the rotation of the upper body unit.
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As the down swing progresses, the left arm must remain held close to the right shoulder whilst the right shoulder remains in total control of the rotational movement of the upper body unit.
(This photo is not entirely correct because the left arm should be closer to the right shoulder at this point in the down swing movement but the photo is intended to hightlight the right shoulder control.)
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I have continue to focus on the right shoulder as being the overal contolling factor right up to contact with the ball, but importantly, will continue to do so as the right arm is fully straightened as the club head moves through the contact area.
(This photo is not entirely correct because the left shoulder should be in a slightly higher position at this point of impact, but the photo is intended to hightlight the right shoulder control.)
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It is absolutely vital that the right shoulder begins to rotate
under the chin as soon as the club head strikes the ball.
This will ensure that the movement of the right shoulder will
push the right arm/ passive arms/golf club swing to the bottom
of the swing arc.
Therefore to ensure success in this task the upper
body angles must be strictly maintained and the head must
be held in such a position so that the left eye is slightly behind
the ball position until the club head reaches the bottom of the
swing arc.
This is one of the most important basic principles of the
golf swing, not only to increase the accuracy of the shot but
also to inject extra power into the golf shot.
When this shoulder movement is performed
correctly it ensures that the club face remains square to the
target line for that extra distance as it moves through the contact
area.
Please note.
Most amateur golfers do not maintain
the upper body angle until the club head reaches the bottom of the swing arc, they
only maintain the upper body angle until the club head makes contact
with the ball, simply because they assume
that once the ball has been struck it is not that important.
Therefore as soon as the ball is stuck they begin to straighten
the body thus causing the right shoulder to move laterally towards
the target area -- instead of forcing the right shoulder to rotate
under the chin from the moment the club
head strikes the ball.
However you must maintain the upper
body angles whilst the right shoulder is forced to rotate under
the chin.