This was actually an answer to an email from a student asking about how far to take the club back on the backswing and what happens, but I thought I'd add it also to "The Backswing" section to help clarify.
My thoughts on this could be a book. FYI, there has been quite a bit of discussion already on this in the forum & blog. In a nutshell… think about what “impact” needs to look like, and then work backwards.
Impact, on a solid, square golf shot only looks one way. Now, there are many variations, that cause different results, but essentially... the shaft will be in line (maximizing the strength) of the front arm, being supported by the back wrist, with a square club face, at just the right point of the swing arc, and all that is being moved by the body’s rotation (the body is unwinding moving that arm/impact shape, around to the left for a right hander). So, how can we arrive into that position reliably, and repeatedly?
Well, the less we move the better. We setup the shaft and hands like we need impact to be, and then only move Large Muscles, hoping to maintain the integrity of the impact shape… that means, the less hinging, and elbow bending and arm separating, and arm lifting (all the fun things the arms/hands/elbows instinctively like to do, to try to generate a “hit-at-it" action by impact), the easier it will be to return to that impact position we started with.
Okay, that’s a mouthful, but what did we learn. The more we can return to impact with the shaft correct and the face square, the better!
Senario: If you setup correctly, use your shoulders to move the arm template back 2’, then rotate through and not change a thing, you get x. A straight shot, that goes some distance. Now, we need more distance, so we go back a little farther with the shoulders controlling the arm template and get x+ … great. What this leads to is, eventually, your swing, as you make your backswing longer and longer (trying to go farther and farther), will start to break down as other body parts try to help… but, they don’t help, they just break down the impact shape we need… and then we hope magically that everything will realign by impact… not going to happen. PLUS, what good does hinging do, if we need a straight line with the front arm at impact?? Actually, it makes you FLIP instead, which changes the club face loft & direction and most likely cause you to miss the sweet spot.
Sorry, wish it was a simple “do this” and you’d know what to practice, but you have to find where your swing breaks down on the backswing… then learn to maximize that spot just before. If that is 3/4 swing in your mind then play that! It really is about efficiency on the backswing, not length. When in doubt… shorten it until you get solid and straight.
Oh, btw… if you think about hammering a nail… if you use your wrist, you get x… if you use the wrist to "hold a shape" instead, as the arm controls the hammer you get x+, then if you add the shoulders, to control the arm that controls, the wrist, to move the hammer, you get x++ … you get the idea.
The most important benefit to learning to use the Larger Muscles is “control” and “repeatability”. This gives much more consistency with direction and centeredness of impact. We want to move the ball with our entire body mass accelerating, not just the mass of the club head flipping… or occasionally like most Pros, the club and the arms moving the ball, but almost never do you see any Pro using the entire body through impact on a full swing (yet...it's coming). Some have learned to use the entire body rotating through impact for short controlled pitch shots vs. hands.