Actually, in many cases, it's the result of poor shoulder mobility. This ball-and-socket joint, and the muscles that surround it, play a huge role in swinging the club correctly. Poor flexibility forces many golfers to let their arms collapse at the top of the backswing or let the left elbow jut toward the target during the through-swing. How do you know if you have good mobility? Dr. Greg Rose and Dave Phillips of the Titleist Performance Institute (@mytpi) demonstrate a test you can do to check both your shoulder mobility and your scapular stability (we'll save that discussion for another week). Check out their 90-90 test here.
If you find that your shoulders are holding you back, click on the video below for two exercises, and a pre-round warm-up move that can help.
Ron Kaspriske is the fitness editor of Golf Digest.