The wrist is the joint between the hand and the forearm. It allows for the positioning of the hand relative to the forearm. Muscle contractions around the wrist allow the hand to be positioned in various ways relative to the forearm. The basic wrist movements include:
You can isolate the hand movement around the wrist joint by holding your right forearm with your left hand to eliminate forearm movement. Then, start moving your hand forward, backward, upward and downward. Focus on the muscles that you are using in relation to each movement. Rapid repetition, perhaps with a light weight in the hand, will fatigue the specific muscles causing the movement. This fatigue will give you an intuitive sense of the muscles being worked by the movement.
In golf, we are looking for a wrist movement that causes the club to go away from the target on the back swing and toward the target on the downswing. This movement will propel the ball down the fairway toward the target.
Suppose one grips a golf club with both thumbs on top of the shaft when the club face is perpendicular to the target. In this situation, palmar flexion in the lead wrist and dorsi flexion in the trailing list produces a backswing that goes directly away from the target. Dorsi flexion of the lead wrist and palmar flexion of the trailing wrist will move the club directly toward the target.
Suppose one wanted to use radial abduction and ulnar adduction in the swing. With both thumbs on top of the shaft, ulnar adduction in both wrists would lift the club up, and radial adduction would lower the club. The action would not propel a golf ball down the fairway toward the target. Instead, it would drive the ball into the ground.
The only way radial abduction and ulnar adduction will propel the ball down the fairway is to place both thumbs at the side of the shaft when the club face is perpendicular to the target. This position is 90 degrees from the position discussed above. One gets both thumbs at the side of the shaft by rotating the forearms. As we shall see in the next chapter, this setup rotation will eliminate the forearm roll, which is a significant power source in the golf swing.
The two examples above illustrate that wrist movement and grip position on a club whose face is perpendicular to the target need to be considered together.
When the club face is pointing toward the target, the standard teaching is to grip the club so that the thumbs are at somewhat at the side of the shaft away from the target. Both thumbs are pointing toward the trailing shoulder. This is considered a "strong" grip.
For beginners, this teaching has some logic. Beginners often lack either the strength or the timing to get the club face perpendicular to the target at impact. The club face is open and the ball typically slices. A "strong" grip is a cheating mechanism that helps beginners to cure their slice.
To propel the ball down the fairway toward the target, this teaching would require the lead wrist to move through a combination of palmar flexion and radial abduction on the back swing to get the club moving directly away from the target, and dorsi flexion and ulnar adduction on the downswing to the club moving toward the target on the downswing. The trailing wrist would execute dorsi flexion and ulnar adduction on the back swing, and a palmar flexion and radial abduction on the downswing.
A better approach is to place both thumbs on top of the shaft when the club face is perpendicular to the target at set up. In the back swing, the lead wrist would execute a palmar flexion on the back swing and dorsi flexion on the downswing, while the trailing wrist would execute a dorsi flexion on the back swing and a palmar flexion on the downswing. This approach is better for these reasons: