Three bones come together at the elbow joint. The humerus is the bone in the upper arm. The radius and ulna are the two bones in the lower arm. Different portions in the elbow joint allow the arm to bend or straighten at the elbow and to rotate clockwise and counter-clockwise at the elbow.
We shall discuss bending and straightening the arm at the elbow in Chapter 5. The more important movement is the rotation of the forearms clockwise and counter-clockwise at the elbow.
The rotational movement is caused by muscles near the top of the forearm. One end attaches to the bone in the upper arm (the humerus) and the other to the two bones (ulna and radius) in the forearm. They operate "across" the arm, so that their contraction causes the rotation.
You can observe the clockwise and counter-clockwise rotation if you hold your upper arm stationary with one hand to immobilize it, and then rotate the forearm. You should observe that your wrist can rotate from facing up to facing down. This is a rotation of almost 160 degrees. See the pictures below for the right arm.
Note that this rotation is separate and independent from cocking and uncocking the wrists, as the pictures illustrate.
By rotating your lower arm clockwise and counter-clockwise quickly for a while, you will fatigue the muscles whose contractions are causing the movement, and will get an intuitive feel of the muscles involved.
Grip a golf club in both hands, hold it in front of you, and try to rotate the right and left forearms clockwise without involving other movements such as cocking and uncocking the wrists, or moving the upper arm in the shoulder socket, or rotating the upper arm in the shoulder socket. Then, rotate the club counter-clockwise. You should observe considerable movement of the club face. It is this movement that generates club head speed and distance in the golf swing. We call this movement the forearm roll.
Some advisers recommend against the forearm roll, but as we shall see in Chapter 12 on modeling the golf swing, the forearm roll, properly executed, is a significant power source that should not be ignored.
The angle between the club head and the forearms can range from about 90 degrees to about 180 degrees. There is considerably more movement in the club head when the angle between the forearm and the club shaft approaches 90 degrees and less movement when the angle approaches 180 degrees. When the angle is 180 degrees, rotating the forearm rotates the club face, but does not cause the shaft of the club to move. Maximum movement occurs at 90 degrees.
The angle of the gripped club to the club shaft makes a difference. This angle is determined by:
In terms of the position of the hands relative to the forearms, we saw in the previous chapter that the muscles in the forearm can pull the hand towards the radius bone (radial abduction - movement toward the thumb) or toward the ulnar bone (ulnar adduction - movement toward the little finger).
Radial abduction will increase the angle between the forearm and the shaft of the golf club, and enhance the effect of the forearm roll. Conversely, ulnar adduction will decrease the angle between the forearm and the shaft of the club and detract from forearm roll. Whatever the extent of radial abduction or ulnar adduction, it is important to maintain a constant amount throughout the swing.
The other factor that affects the angle between the forearm and the club shaft is the grip in the lead hand, specifically whether one grips the club along the finger line, as in the left picture or in palm, as in the right picture.
For any amount of radial abduction, the two different grips positions can change the angle between the forearm and the club shaft by 10 degrees.
If one grips the club along the finger line and at the same time maximizes radial abduction of the wrist joint, the angle between the forearm and the club can approach 90 degrees.
A 90 degree angle between the forearms and the club shaft is a problem in several respects:
Our golf model, discussed in Chapter 12, observes that an angle of 120 degrees gives slightly more distance than 130 degrees, which in turn gives noticeably more distance than 140 degrees.
Experiment with lowering the angle between your forearms and club shaft to the 120 to 130 degree range, by adjusting both your grip and your hand positions relative to the forearm.
Note that to make different angles work, you will likely need to make modest adjustments to the amount of knee bend, the degree to which you bend forward at the hips, the distance between your feet and the ball, and the angle between your upper arms and the spine at the start of your swing.