The " upper body unit" is the shoulders and
the arms which has been formed into a compact triangular shape by simply holding the elbows as close together as is physically possible and holding the Latissimus Dorsi muscles in a firm condition, but also keeping the arm in a passive condition,
(It is absolutely vital that the upper body unit is held in this very compact condition throughout the complete swing.)
During the back swing movement the mid/lower back muscles force the compact upper body unit to rotate to the end of the back swing movement whilst the hips put up a slight resistance and also whilst the head remains firmly held in the frontal facing position.
However during the down swing movement and the follow through movement, once the hips have begun to rotate towards the target area and created a full twisted effect of the whole body, the rotational movement of the hips and the upper body unit rotate in complete coordination .
( There must a slight lag after the hips begin to rotate towards the target area, before the compact upper body unit is forced to follow.)
During the down swing movement the rotational movement of the compact upper body is totally controlled by the hip movement at all times.
This compact upper body unit is formed by holding the elbows
as close together as is physically possible.
During the down swing/follow through movement in addition to the shoulders and the arms being held as a solid one piece unit, the left arm must be held close to the right shoulder until the club head strikes the ball and then at the point of impact the arms are forced to interact, therefore you need to hold the golf club with a light grip so that the flexibility of the wrists can be fully utilised.
It is vital to understand is that as the shoulders and the arms rotate whilst held together as a very compact unit --- the only time the arms move independently of the shoulders is when the arms interact at the point of impact.
(The action of making a back swing, automatically causes the right arm to fold thus forcing the arms to move independently of the shoulders, as do the action of making a down swing movement where the right arm begins to unfold, but these action are totally involuntary and therefore cannot be stopped.)
I cannot stress too strongly how vital the action of holding
the upper body unit in this very compact unit throughout the complete
golf swing contributes to playing very good golf.
You must be conscious of the left shoulder
as being in over-all control as you force the compact upper body unit to rotate.
( A correct back swing movement is absolutely vital
to a successful golf swing.)
You must keep the elbows close together whilst the back swing movement is performed
At the end of the back swing movement the rotational movement of the shoulders should cause the left shoulder to to rotate under the chin
During the down swing movement, after applying pressure to the left foot, the right hip forces the hips to rotate towards thus exerting a continual pulling effect upon the compact upper body unit.
Therefore you must allow the hips to begin to rotate towards the target area for much longer than you imagine in order to fully twist the whole body to its maximum.
But importantly, you must continue to hold the upper body unit as a very compact condition whilst the hips force the upper body unit to rotate and also hold the left arm close to the right shoulder.
But all this must be performed without allowing
the hips or the head to sway away from the original address position.