TRANSITION POWER
The X-Factor Stretch
X-Factor describes the relative rotation of the shoulders to the hips during the golf swing. The maximum value occurs at or near the top of the backswing. It's a popular concept.
In an efficient swing, the hips rotate towards the target first followed by the shoulders in the transition from backswing to downswing. The effect is to increase the rotational stretch between hips and shoulders during the transition. The resultant increase in the X-Factor is known as the X-Factor stretch. When it occurs, the rotational muscles in the upper body contract with more force in the downswing than if no X-Factor stretch had occurred.
This stretch-shorten cycle is a source of extra power that some biomechanists consider to be as important as the power generated by the X-Factor itself. An X-Factor stretch of 3 - 5 degrees is typical for top players.
The X-Factor stretch leads us to think of the backswing as more than just getting into a good position for the downswing. An efficient backswing results in an increase in the dynamic tension of thorax rotational muscles that allows the golfer to achieve maximum muscle contraction in the downswing. It translates into more power and distance.
Here we see a player generating nearly 4 degrees of X-Factor stretch. Translation: more distance.