Feel the pull: At the top, your lead lat should be engaged and ready to pull your upper body into its forward rotation.
There's some debate about how to generate power as you start down. Many golfers think it comes from driving the legs, but it can be difficult to make consistent contact if your legs get too active. Your legs should play a supporting role, but the real key to starting down correctly is to engage the left side of your torso (for righties), particularly your latissimus dorsi, or "lat" muscle.
Big hitters have strong lats, which run from the shoulder blades to the hips. At the top of the backswing, your lead lat muscle should be fully stretched and ready to create that extra burst of clubhead speed needed for a big drive. To tap into this power source, feel that lead lat coiling as you make a full backswing. Then start your downswing by letting it release and pull your upper body toward the target.
, a Golf Digest Teaching Professional, is based at Treetops Resort, in Gaylord, Mich., and Tiburón, in Naples, Fla.