Jim McLean’s popular golf instructional book, The X Factor, describes the importance of creating a big shoulder turn against restricted hips. By using a SportsSense Motion Trainer (SMT) developed by Mike McTeigue, Jim was able to monitor the amounts of shoulder and hip turns in different swings. He found that tour professionals, especially the longer hitters, tended to make big shoulder turns with relatively small hip turns.
There is no exact measurement of how much you should rotate your shoulders or hips but as a general guideline, you want to make the biggest shoulder turn you can while keeping the lower body as passive as you can. To make a full shoulder turn, you will need to naturally rotate your hips some but the key is to make sure that you don’t overturn your hips and lose out on torque.
This is a pretty common biomechanical limitation in some people, especially as they get older. If you find yourself straining to get a full shoulder turn while keeping your lower body passive then experiment by allowing yourself a bigger hip turn until you can get at least a 90 degree turn with the shoulders. Make sure that when you rotate your hips that you keep your right knee flexed some.
You can also modify your stance to help increase or decrease rotation. Many golfers like to flare out their left foot (for a right handed golfer) some to help with the unwinding rotation on the downswing (pictured). If you want some help with rotation on the backswing, you could also flare the right foot away from the target some. Keep in mind, though, that if it aids rotation in one direction that it will hinder rotation in the other.
Finally and perhaps most importantly, remember that the hips lead the downswing sequence. If you look carefully at the swings of tour players, you’ll notice that some of them start unwinding the hips before the backswing is fully finished. You probably don’t want that as a swing thought but just know that the downswing starts with the hips unwinding. This should encourage your torso to unwind which then encourages the gradual acceleration of your arms and then club.