In each shoulder, the scapula and clavicle make up a bone structure which holds the shoulder socket. This bone structure is held in place by muscles attached to the body's core. The bone structure can move around. Each shoulder socket can move upward (as in a shrug), downward, forward and backward, and points in between.
One can raise and lower the scapula and clavicle. This occurs through the contraction of muscles attached to the bone structure, and the spine, neck and skull. The contraction of these muscles pulls the bone structure up. Muscles attached to the bone structure and the ribs can contract to pull the bone structure down (although when standing, gravity also works).
One can also move the bone structure forward and backward. The forward movement comes by contracting muscles which connect the bone structure to the front ribs. The backward movement comes by contracting the trapezius, which attaches the bone structure to the various vertebrae in the upper part of the spine, and the rhomboids, which attach the bone structure to vertebrae in the middle of the spine.
To get a sense of the potential effects of this movement, sit in a chair with a low back that does not impede the movement of your shoulder, immobilize all joints but the shoulder socket, and move the shoulder socket forward and backward. You will notice that you can move your shoulder socket forward by about three inches, and backward by the same amount. The extent of the movement is illustrated in the following pictures, with the ear as a reference point.
In the golf swing, the "up and down" movement of the shoulder socket does not add distance in the golf swing. You can visualize this by gripping a golf club and executing the up and down movement. The movement does not propel a golf ball forward.
Moving the lead shoulder socket forward toward the front centre of the body and the trailing shoulder socket backward away from the front centre on the back swing, and reversing the movements on the downswing, create a rotation around the spinal column that can add distance to the golf swing.
To understand where the distance comes from, picture the shoulder sockets as two points on the circumference of a circle, for which the centre is the spinal column. In the illustration, the yellow dotted line depicts the line between the two shoulder sockets at the start of the swing. The red dashed line depicts the position of the shoulder sockets in the back swing, with the lead socket moving forward and the trailing shoulder moving backward. In the downswing, the shoulder sockets would move back to the start position and then go beyond in the follow through, as depicted by the blue solid line.
How important is this rotation? If shoulder sockets are 13 inches apart, and each shoulder socket can move forward and backward a straight line distance of 3 inches, then the shoulder socket movement will create a rotation of 26.7 degrees.
In addition to the rotational effect, the forward movement of the shoulder socket in the back swing is important because it allows a fuller range of movement of the lead upper arm in the shoulder socket. The previous chapter noted that the body and chest can impede the range of movement of the upper arm in the shoulder socket. Moving the shoulder socket forward creates more room for the upper arm to clear the chest and upper body. This enables a wider range of movement for this arm.
For many golfers, the movement of the lead shoulder socket forward toward the chest occurs unconsciously in the back swing while the golfer is moving the lead upper arm toward a full back swing. What some players miss are, on the downswing, the rotation of the lead shoulder socket from the forward position to the backward position and the corresponding rotation of the trailing shoulder socket from the backward position to the forward position. This is a missed opportunity for power and distance. Next time on the course, test to see whether you are achieving rotation with your shoulder sockets.
In some golf swings, the lead shoulder socket moves upward toward the neck, rather than backward, in the downswing. A sign of this movement is a high, rather than low, follow-through. This movement in essence stops the rotation, and causes a loss of distance.
Watch the practice and ball-striking swings of professional golfers, particularly on short iron shots. The follow-through actions are very low, and typically look as if the professionals are purposely focusing on moving the lead shoulder socket backward.