The term X-factor is used to describe the rotation of the shoulders in relation to the hips throughout the swing (Cheetham et al 2011; Sweeney et al 2011). The X-factor enhances the power of the golf swing by means of utilising the stretch shortening cycle (SSC). The SSC is the rapid change from an eccentric to concentric muscular contraction. This rapid eccentric stretch of a muscle before it is concentrically contracted produces a more powerful contraction than if a muscle was contracted purely concentrically, most likely due to stored elastic energy in the muscles and tendons involved in the action (Flanagan and Comyns 2008; Hume at al 2005). Modern golf swings are excellent examples of a powerful SSC motion. During the backswing the hip, trunk/torso, and shoulder muscles are quickly stretched, loading them with elastic energy, prior to being quickly shortened or contracted on the downswing. While this stretch of the main muscles involved in the swing is important, the mechanics of how this happens seems to be even more so (Hume at al 2005).