Arm Putting (Picture 1) is allowing
your arms to swing the putter.
For solid contact you want a putting stroke that minimises your upper body movement.
The use of your arms in your putting stroke contrasts with a deliberate rocking motion of your shoulders to lead your stroke.
When you set up correctly, your arms, wrists, hands, and shoulders form what is commonly referred to as the Putting Triangle.
The image you should have when putting is that of swinging the triangle.
This is best achieved by not moving your shoulders consciously, but allowing them to respond to the movement of your arms.
A shoulder-driven stroke (Picture 2) leads to excessive upper body movement with your head tilting to the left on your backstroke and to the right on your forward stroke.
As Todd Sones writes in his book Lights-Out Putting "The primary key to a really good arm stroke is understanding that the stroke is controlled by the arms. The shoulders will move, but only as a result of the movement of the arms."
With better and faster greens the former use of the wrists in putting has all but disappeared from instruction and from the way pros putt.
The recommendation now is to use a pendulum putting stroke that keeps your putting triangle intact and eliminates any hinging of your wrists.
Whereas some hinging of your wrists is allowable on long lag putts, for every other putt your putting triangle should move rhythmically backwards and forwards like the pendulum on a grandfather clock. At the same time the tempo of your putting stroke should ideally match the natural tempo of gravity.
Everything in putting should be directed to making consistent and solid contact with your putterface square to your target line. When you putt with your arms, your head doesn't move, but remains steady over the ball.
This leads to greater control of your stroke. A head that rises and dips, a feature of a shoulder-driven stroke, makes this task more difficult.
Luke Donald in an article in the Golf Digest on The Do's + Don'ts of the Short Game explains that the tilted shoulder stroke decreases the loft of the putterface going back and increases it through impact more so than in an arm stroke. This makes solid contact of your putter on the ball difficult to achieve without constant practice.
Solid contact is pivotal to good distance control as well as influencing to a lesser extent directional control.
Strike your ball high or low on the putterface, or towards the heel and the toe, and you will have certainly compromise the distance your ball will travel.
To putt well as described by Beverly Lewis in her book Perfecting Your Short Game the clubhead must be swung on a very shallow arc, so that there is no suggestion of hitting down on the ball.
A drill that Dave Stockton advocates is holding your left shoulder with your right hand and making some one-handed strokes. This will give you the sensation of keeping your shoulders more or less level, and an understanding of what Arm Putting is all about.
1+2 = www.golfdigest.com
3 = Dave Stockton's Book Unconscious Putting / Photo by J.D.Cuban