The lower body starts the downswing, and how you use it will largely determine how far you hit the ball. You'll leave so much distance on the table if you don't allow your pelvis to first slide and then rotate toward your target. The move you want to make is like a powerlifter's squat.
To demonstrate, I've stuck an inflatable ball between my legs. I'm squeezing the ball with the insides of my thighs as I swing to the top. I can sense my glute and core muscles working, and my lower body feels stable. From this position, I start down by pushing into the ground. Notice how my knees turn out, especially my left, and the ball drops. This gets my pelvis rotating forward. It also enables me to use the ground to create force, which helps generate clubhead speed. Best of all, I'm staying in a very stable position: My knees are stacked over my feet—that's the powerlifter part—and I haven't swayed at all. So let your knees flare out as you start down, and you'll pick up some noticeable distance.
Golf clubs are so light (less than one pound), you don't need quality body action to swing them. You can get away with using only your arms. But if you grab a medicine ball and mimic your swing, you'll find you have to stabilize your pelvis with the core muscles, push into the ground for leverage, and rotate your body toward your target to throw the ball. You'll learn proper body action during the swing without even picking up a club.
SEAN FOLEY, a Golf Digest Teaching Professional, works at the Core Golf Junior Academy, outside Orlando.