RANGE OF SWING MOTION
Golf requires a near maximum range of motion in both backswing and downswing for best performance. in the backswing muscle flexibility, joint mobility, and balance are generally more important than strength. The trail side shoulder externally rotates and retracts while the trail side hip internally rotates. And there must be sufficient strength in core and lower body muscles to provide the stability needed for a balanced rotation around a stable lumber spine. Any limitations will restrict the ability to execute an efficient swing and could lead to injury.
Strength in the downswing and lead side lateral stability is easier for most golfers to appreciate. But the sequence of movements used to initiate and execute the downswing is critical for maximum power and clubhead speed. For example, a golfer who initiates the downswing with the shoulders may generate forces that push the arms away from the body and put the club in an over-the-top swing plane. Improving hip stability or mobility or both will help in transferring power from the lower body and reduce stress on the spine thereby making it easier to keep the club on plane to the ball.