For the Back Stabilizer Exercise, you're going to need to get down on the floor. Lie on a mat and put a towel under your head for comfort.
This exercise will teach you how to get your shoulders down, into the box, as opposed to being up and in the rectangle. As you work through this program and do some of the other lessons on the site, you'll understand how important this is to your golf swing.
The first thing you'll do is pull your shoulder blades down as far as you can. You should feel like your shoulders come down and really tuck in; this is called being "in the box." Your shoulder blades will move down toward your belt.
Pull your shoulder blades down toward your belt - this is "in the box"
Now pull your shoulders up toward your ears. Your shoulder blades will probably move a total of four or five inches, down and up, as you do this.
Bring your shoulders up to your ears - this is "in the rectangle"
The Box & the Rectangle
When you pull your shoulder blades down, you're contracting your lats. This is what we mean by being "in the box," activating those big muscles in the box shape that defines your core or torso.
Contracting your lats and pulling your shoulder blades down into the box is the correct position for the backswing. Using these muscles helps you get more power in your swing.
When you pull back up toward your ears, you're disengaging the lats, disconnecting from your core, and going up "into the rectangle." You're using the muscles in the rectangular area across your neck and shoulders. These are not the muscles you will be using in your golf swing.
A Little Extra Challenge
Do 15 repetitions of this Back Stabilizer Exercise. You can do as many sets as you like. This exercise will help strengthen these back muscles, as well as making you more aware of what it feels like to pull your shoulder blades down and into the box.
Now we'll add in some arm movement to make it a little more challenging.
Go ahead and pull your shoulder blades down, but this time move your arms as well. Your arms will come down to your sides. Don't lift them up off the ground; just keep them in line your torso and the rest of your body.
Repeat with arm movement - pull down toward your waist
Now pull your shoulders back up toward your ears, bringing your arms along and, again, making sure they stay parallel to the ground.