Extensor Action.

Extensor action simply means to straighten the right arm and this is done through a conscious muscular effort via the tricep muscle of the right arm.

The right arm needs a feeling of always pushing out to seek the maximum radius of ones elliptical arc, this gives substance/structure to the left arm allowing downward pressure/mass to be applied to the golf ball, think of the left arm as a cable on a suspension bridge, should the right arm always be extending the left arm will naturally be straight with a hidden stored potential energy just like that of the cable, if one was to cut this the cable would pull violently apart.

So how does one apply this within their own swing?

It's all in the right arm and concentric (shortening muscle) application of the right tricep, in ones own body it would feel as if the right tricep is always active in an isometric (static) hold but in reality in the backswing the right arm is folding and in the downswing it is straightening. The right arm is always seeking a straight condition though not succeeding until a good foot or so past impact, impact interval and separation, this area is called the followthrough whereby both arms are straight, (the only time this happens in the golf swing).

The many benefits of extensor action include:

full extension of the left arm;

full extension of the right arm at follow through (p7.5);

the correct rate of clubface closure.