|Bradley's Lateral Bend|
The transition--back still facing the target--begins when the spine bends laterally to the right, blended simultaneously with a rotational pivot around the left side (i.e., "bend-rotate"). This assumes and demands that the preceding thoracic spine position was a lateral bend to the left at the top of the backswing, left shoulder pointing down; if you stand up on the backswing (left shoulder too high), lateral right bending will send the left shoulder too high during the downswing.
Kelvin Miyahara calls this "engaging the spine engine," meaning that it forces the facets of the vertebra to behave like gears to drive the swing and keeps the lower back in a state of safer lordosis. He states that this lateral bending move must occur BEFORE starting down, but in reality I look at it as if simultaneous bending and rotating ARE "starting down."
With proper right lateral bending, you will notice a few "fundamentals" that occur automatically. The left hip bumps both towards the target and back to the original tush line (while the back is still turned away from target), and the weight shifts into the left leg. This left hip tush-line-return move blends immediately with a left side rotation (i.e., "clearing the left side"). An analogy to the left hip rotating back and around is that the right foot rolls inward and right knee moves somewhat linearly towards the left knee (also analogous to the right hip "dropping"--more on this later). This left hip tush-line-return-and-rotate move is crucial to create space for the right lateral bend; otherwise, the arms will crash into the body if you merely bend laterally to the right WHILE sending the right side out towards the ball. Also, you will notice that the arms drop down automatically when right lateral bending without the loss of wrist angles, and the right elbow drops in close and in front of the right hip (the lateral bending forms a "pocket" or "catcher's mitt" in front of the right hip to receive the right elbow). The right shoulder will also drop very close to the right hip--again the back still slightly facing the target--and the club shaft will automatically shallow or flatten. The secondary spine angle will also increase (upper swing center leaning away from target more than at address); you will feel your head staying way back at impact. You will notice that the right elbow still has a generous bend in it at impact. Your hands are easily well ahead of the ball before the club head reaches it; the right elbow can easily lead the right hand (externally rotated humerus), because it was able to fall unhindered back into the "pocket" (i.e., front of right hip) created by the side bending. The tip of tail bone will actually move first towards the target and then away from the target, and lateral hip sliding is kept to a minimum (i.e., the left hip stays "inside" the left foot). All of these things happen somewhat automatically as a result of the correct bending-rotating motion.
A note about the arms, wrists, and hands: They should not be doing anything until near impact; the motion of lateral bending and rotating, as described above, provides all the impetus needed to get the arms and club to automatically start down and reach a position at or near pre-impact. This totally supports Joe Dante's assertion in his famous Four Magic Moves book that the arms don't do anything until near impact.
Bending-rotating is what Monte Scheinblum refers to as "bump, dump, and turn," although I don't believe the arms "dump" into the body as he explains; the right lateral bend--properly performed--makes room for the arms and club to swing down in front of the body unhindered. Be aware of a tendency to stand up when doing this; correct lateral bending is a form of "covering" the ball. If you "stand up" it means you didn't really bend laterally; you likely rotated your right side out to the ball.
Elbows Close and Iron Man
As rotation around the left leg begins, the left shoulder should feel like it separates from the chin and realigns with the left leg (as in the Reverse K address position), moving around before moving up. Pretend there's a light shining from the middle of your chest (think of Iron Man) and that light should rotate to shine down towards the ball at the same angle established at address, and then begin angling up in front of the left foot, as the chest rotates through impact ("return cover angle" or primary spine angle); this is called "covering the ball" with your chest. The covering "chest light" should lead the arms and club back to the ball. The right elbow should swing down past the right hip unhindered (i.e., no crashing into the rib cage); the right arm feels as if it straightens towards the target underneath the left shoulder and is totally unhibited by the right side (it may lightly brush but should not crash into the right side). This is encouraged by keeping your elbows close together back and through.
At the finish, you should feel very balanced and fully on the left leg, the pelvis will be forward of the upper torso, the left hip will feel high and jutted away from the target line, the upper torso will be leaning towards the target line slightly (i.e., head on a pillow), and the right shoulder will be rotated toward the target and touching the chin. These are all signs that posture has been maintained; otherwise, expect fat, thin, and weak, pulled shots.
You've likely seen the drill where the pro advises golfers to place their left hand on top of their driver, with the driver shaft vertical and the club head sitting on the ground, and practice swinging their right arm under their left arm. I believe this drill is trying to get you to feel right lateral bend. You can also do the windmill drill: Stretch your arms out so that they're horizontal to the ground and take your address posture; rotate back and through so that each hand points down at the ball.
Another way to encourage right lateral bending is to feel like your right hip drops down towards the ball during your downswing, which automatically gets your right shoulder to drop, thus initiating a right lateral bend. However, you must remember that it all begins with a left hip bump towards the target (back still turned) and a right elbow that drops unhindered back in front of the right hip.
Lateral bend, although it seems simple, is really quite complicated. Simplistically, it is just a side bending like the picture above. But add in that this must be done at a while you're at the top of your backswing with shoulders turned, while in the absence of downswing shoulder rotation (if for a brief moment), while your spine is being bent to the right, your shoulder is pulled down behind you while increasing lumbar lordosis (explained later) and while the rotator cuff muscles are externally rotating the arm. Now this seems very complicated.So when does lateral bending occur? It should start during transition.
The key is in varying the amount of lumbar lordosis during the swing. Also we are combining the lateral bend with the lumbar lordosis to set the spine gears in place. Any disconnecting of the gears at any point prior to contact will produce an adverse swing reaction (most likely, a hip or shoulder stall) that will cause other problems to occur such as casting, flipping, lunging, jumping, etc.