According to teaching pros the main reason for a slice is an outside-inside swing. There’s no questioning the fact that an outside-inside swing will put side spin on the ball creating a slice. However, after analyzing hundreds of golfers I have yet to see a true outside-inside swing.
In order to get the club head to travel on an outside-inside pathway, you will have to do one of the following: have the clubhead in front of the body at the end of the backswing, bring the clubhead forward rather than downward as you begin the downswing, or there is no forward weight shift which allows you to bring the clubhead across the body plane. If you do the latter, then you usually must take a step backward.
In essence, instead of bringing the arms directly downward after taking a backswing you must swing the club in front of the body and then down and across. As you do this you will most likely be shifting your weight or your body backward to accommodate the crossing of the body plane. This is an unnatural movement that golfers typically do not do. Because of this I discount this as a major reason for a slice, even though it is possible to see it happen.
Another reason suggested for the slice is that you in this way you you you hold the clubface open before and during contact with the ball. This puts side spin on the ball resulting in a slice. This is a valid reason since an open clubface at contact will cause a slice. However, it is rare to find a golfer who holds the clubhead open. If this is the problem then it is relatively easy to fix.
To prevent having an open face at contact, it is sometimes recommended that you bring the right foot back in your stance so that you limit body rotation. This may be an effective fix if you sliced on every shot. However, few golfers do this. Because of this you may find yourself creating other problems associated with this change in your stance. For example, by bringing the right foot back you have less power which will decrease the distance of your drives.
In my work I have found that most often the slice is due to insufficient rotation of the arms to square the clubface prior to contact. In other words, there is insufficient lateral rotation of the left arm and insufficient medial rotation of the right arm. Golfers who are more “wristy” usually have insufficient supination of the left forearm and insufficient pronation of the right forearm.
To cure the slice, it is first necessary to analyze your swing movements to see where the problem lies. By determining which actions (or lack of actions) are responsible for the slice, and then correcting them with specialized strength exercises. In thisyou develop the ability to execute the actions needed to prevent the slice. The key is to find the main problem and correct it and not create a new problem to resolve an old one.
Specialized strength exercises strengthen the muscles as they are used in the swing. Most effective for this is the Strength Bar which allows you to duplicate the neuromuscular pathway and develop strength at the same time. In other words, you develop strength in the same manner and in the same range of motion as needed to get the clubhead square to the ball.
Best program to develop strength and develop the neuromuscular pathway is the 1 x 20 RM strength training program. It not only reinforces the correct pathway and actions that occur but you develop strength in the same range of motion as needed during the swing.
For more information see Explosive Golf. There are sequence photos taken from live digital film of professional golfers to show you exactly the actions that should occur and specialized strength exercises that duplicate these actions. There is also an Explosive Golf DVD that illustrates the specialized strength exercises.
For information on the 1 x 20 strength training program see The Revolutionary 1 x 20 RM Strength Training Program.