The shoulder consists of three bones: the collar bone or clavicle; the shoulder blade or scapula, and the upper arm or humerus. The term "shoulder joint" usually refers to the joint where the upper arm attaches to the shoulder blade (scapula).
This joint is a "ball and socket" joint. The ball is the rounded end of the humerus, while the socket is a dish-shaped structure in the shoulder blade (scapula).
This ball and socket joint allows the upper arm to move in a number of directions, limited by the socket and the flexibility of the muscles holding the bone in the socket. Two movements are singled out here: up and down, and toward and away from the body centre.
One can get a sense of up-and down movement by starting by standing erect with the arm vertical to the ground at one's side, then moving the arm up to the front till it is horizontal to the ground, and continuing to move it until it is vertical to the ground. This movement encompasses about 180 degrees.
One can get a sense of the movement toward and away from the centre of the body by standing erect and holding the upper arm straight out in front horizontal to the ground, moving the upper arm on the same horizontal plane as far as it will go to the centre of the body, then moving the upper arm on the same plane away from the centre of the body as far as it will go.
When the arm is straight out in front horizontal to the ground, the movement of the upper arm to the centre of the body from the start position should be about 70 degrees. The movement from the start position away from the centre of the body can be almost 90 degrees.>
In carrying out this movement, take care not to move your shoulder socket forward or backward. Moving the shoulder socket forward and backward is another movement to be discussed in Chapter 6.
Now, instead of starting with the arm horizontal to the ground, lower the arm a few degrees and retry the movement toward and away from the centre of the body on the same level. Continue to retry the movement, each time lowering the level a few degrees. Note that as you go to lower levels, the range of movement to the centre of the body decreases, as the chest and upper body get in the way.
You can get an intuitive sense of which muscles are performing this movement by executing a number of repetitions, perhaps with a light weight, and feeling where the burning sensation occurs.
Essentially, muscles attached on the one hand to the upper arm and on the other hand to the scapula and other bones contract to move the arm in the various directions.
In the golf swing, the lead upper arm is our focus. It provides the power and direction to the golf club. The trailing upper arm primarily moves to accommodate the actions of the lead arm.
Consider the shoulder socket on the lead arm as the centre of a circle. Because the shoulder joint is a ball and socket joint, the lead arm can move around the shoulder socket in a variety of circles. Let us consider some possibilities:
The picture illustrates the three options. The vertical line is the spine. In Option 1, the movement of the upper arm causes the hand/club to trace out a circle. The plane of the circle is perpendicular to the spine. In Option 2, the upper arm is below perpendicular to the spine, but the movement of the upper arm continues to allow the hand/club to trace out a circle. The radius is the same as in Option 1. The plane of the circle follows the radius and is at an angle less than perpendicular to the spine. If one imagines the elevation of the hand/club as it moves around the circle circumference, the track of the club/hand will have an up and down component. In Option 3, the radius of the circle traced out by the hand/club is less than in both Option 1 and 2. The elevation of the hand/club remains constant as the upper arm moves in the shoulder socket.
With Option 1, when one moves from standing erect to the golf swing setup where the spine is tilted forward, it would be technically difficult, if not impossible, to get the club on the ground at address, as one is unlikely to find a configuration of knee bend, forward lean, angle between the club shaft and the forearm, and club length that would end up with the club on the ground. Option 1 was introduced to demonstrate the concept of a muscularly simple movement.
Option 2, when incorporated into the golf swing, is complicated from a muscular perspective, since more muscle groups are involved. It involves getting the right combination of movements across and away from the body centre and up and down. However, when perfected, it will produce power and distance, because the radius of the circle traced out by the hand/club is maximized. This is a good option for the skilled player.
Option 3 is conceptually simple to incorporate into the golf swing. Option 3 requires that the arm stay at the same elevation relative to the spine. In Option 3, the mental thoughts should include keeping the club at the same elevation relative to the spine and not contracting the muscles that move the upper arm up and down. One needs to think only of moving the upper arm across the body toward the body centre on the back swing, and back to the start position and beyond on the downswing. However, there will be a loss of distance off the maximum because of the small rotation circle radius. The loss in distance may be offset by better contact from a simpler swing. The miss-hits should diminish and the average distance should go up. This is a good option for beginners and high handicap players.
The problem with the movement of the upper arm in the shoulder socket is the flexibility inherent in the ball and socket shoulder joint. The upper arm can go in a variety of direction.
One solution to the problem is Option 3. In this option, focus on moving the lead arm across the body toward the body centre on the back swing and away from the body centre on the downswing and follow-through. Avoid trying to move the lead arm up (particularly on the back swing) or down.
If one opts to pursue Option 2, the issue is more complex
In the golf swing where the spine is tilting forward because of the forward lean, the challenge is to get the upper arm to trace out a circle which moves the club head directly away from the target on the back swing, back to the start position at impact, and directly toward the target on the follow through. Getting the correct circle involves getting the correct balance of movements across and away from the body centre on the one hand, and up and down on the other.
One way to get the correct movement in the swing is to assume one's normal setup position, and without a club, swing the lead arm directly away from the target in the back swing and toward the target in the downswing and follow-through. Use your eyes and brain to tell you whether the club is on the correct path. Place the trailing hand on the lead shoulder socket to immobilize it; make sure the lead shoulder socket does not move. Note the range of movement in the back swing; it should be restricted as the upper body impedes the movement. When you feel the restriction, the movement toward the body centre should end. Note the position of the lead arm relative to one's chest; it should be across the chest. Note the position of the lead arm relative to the chin; the lead arm should not be getting up to the chin. Try to get a sense of the balance between the across-the-body and up movements in the back swing.
Now, retry the movement, this time holding a golf club in the lead hand. At the driving range, try to hit the ball straight toward the target from your swing setup position with a one arm movement. Do not incorporate any other movements in the swing; use only the lead arm. Hit a number of balls. If you have problems at first, after you get some skill in the movement, you will start to hit the ball better. At this point, note whether your balls are straight on target, or to the left or right. The ball flight will tell you whether the plane of your swing circle is going directly down the target line. As you continue to hit balls, try to get a sense of the balance between movements across and away from the body centre and up and down, and the limits to your range of movement.
Many players over-swing. In the interest of getting more power and distance, they move the lead arm too much in the up direction and not enough in the across-the-body direction. In some cases, they begin with the proper across-the-body movement, but when they come to the end of their range of movement, rather than stopping the back swing and starting the downswing, they continue the back swing by moving the lead arm up in an effort to get more power. As indicated in the section on shoulder anatomy, there is no practical limit on the range of movement in the up direction, but there are limits on the across-the-body movement. The up and across-the-body movements become unbalanced in the up direction, and the club moves off the desired circular path.
The typical result is a club path that goes from outside the target line before impact to inside the target line after impact (i.e. an outside to inside swing). The corresponding ball flights are a pull hook (closed club face at impact), a straight pull (club face square to the ball path at impact), or slice (club face open to the ball path at impact). Monitor the flight paths of your balls to determine whether you may be over-swinging.
One way to test for over-swinging is to put an object (tee, towel, etc.) in the lead armpit during the swing. If the item falls to the ground in the back swing, the lead arm is separating from the body as it goes too far up on the back swing. This test also becomes a drill to correct the fault.
Another correction technique is to simply realize that if you hold golf club and perform an up-down movement of the lead arm without going across the body, the result will not be the coveted extra distance, but a golf ball driven into the ground. The mental note that going up too much does not add distance should reduce the temptation to over-swing.
A third technique is to monitor the position of the lead arm relative to the chin. If the lead arm rises to the level of the chin, you are probably over-swinging.