[12 piece bucket]

In order for the head (or the spot between the shoulder blades, whatever you use) to maintain the level it had at address, the spine has to bend laterally as it rotates. Try this (and be careful!). Take your address position with your head against the wall. Now, with your arms across your chest rotate your shoulders into the backswing. In order to maintain your spine angle, you have to contract your left obliques (the muscles hidden by the love handles). These are the muscles that bend the spine to the left side. Now rotate into the downswing until the chest faces the target. The obliques on the other side should contract. Still not convinced? If you have a decent back, keep turning your body (you'll have to move your feet, but keep your head glued to the wall), until your shoulders are parallel to the target line, this time facing the opposite direction as you were at address. In order to hit this position while maintaining the spine angle, the back needs to be almost hyper extended.

What's my point in all this? Even if you disregard hip slide (which adds another element of spinal movement), the irony is that in order to maintain the forward bend angle of the spine to the ground, the spine itself is in constant motion. This is necessary because the spine isn't a straight rod, it's curved (even in guys like Adam Scott ). This is why so many golfers have back problems. It's the nature of the beast. We weren't made to play golf.

Nice post.