The 3D Serve:
Upward Swing Part 2
Brian Gordon
Our first article on the upward swing in the serve dealt primarily with the role of the torso or trunk. We identified the "cartwheel" action as most responsible for the transfer of forward angular momentum to the hitting arm.
We then discussed ways to alter the rotational speed of the trunk by changing its orientation in time and space. Finally we saw how the possible variations in the use of the trunk affected the positioning of the hitting arm at contact. (Click Here.)
We concluded that there are different ways to take the racket to the contact point, and these differences are a function of a series of specific joint rotations that can occur in different combinations.
But measuring and describing these components of the upward swing is different from explaining how the upward swing is actually executed.
Joint forces and torques are the engines that transfer momentum upward to the racquet. They drive the joint and segment rotations. But how do players make these joint and segment rotations happen? Let's address that in this article.
Let's start with a basic distinction and see what parts of the motion are driven by active muscle contraction and what happens as a consequence of other motions, what we've called dependent motion effects.