Likewise in the figure below, the contraction stage is similar to that of the closed-shoulder forehand. The figure on the right is an interactive rollover.

In the rotation stage, the shoulders now begin to play a more dominant role. In fact, the shoulders in this example are more rotated that some cases of Agassi's shoulders at the strike stage.

In the acceleration stage, the shoulders are now rotated over 90 degrees from the start. This is an approximation because the degree of rotation can vary widely, and there is no set rule.

In the last stage, the shoulders have rotated still further. There are many examples where this rotation is even more pronounced, and the total degree of rotation can vary. Again there is no rule. The key point is that the acceleration blends into the strike because the combination of upper arm rotation and shoulder rotation can serve to create a nearly straight-line interval. This can best be seen by drawing a diagram of two circles, one tangent to the other, with the smaller one representing the upper arm rotation and the larger circle representing the shoulder rotation. By careful analysis, you will be able to confirm that the composite motion of two rotating circles in this configuration can produce a straight line.