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Torques, Rotation, and Angular Momentum

In my "Master Principles" series, I begin with the concept of "Pull-Push" to describe professional strokes. There is, however, a second force at work that is equally powerful. This second force is torquing, turning or rotating motions. Not only do these rotational motions apply tremendous force and grip to an object, they also lead to Angular Momentum, which produces a rapid burst of acceleration coming into and through contact. Here is what Wikipedia says about pull, push, and torquing forces:

"Torque is the tendency of a force to rotate an object about an axis[1] (or fulcrum or pivot). Just as a force is a push or a pull, a torque can be thought of as a twist."

- Wikipedia "Torque"

Torquing, twisting, rotational forces can be found everywhere in professional tennis, but it wasn't until I started capturing footage at 300fps that I realized just how prominent these moves were. The linear motions come down to pulls and pushes, which are combined with the turning motion of pronation to lead to today's big power/spin game.

"Pronation: An inward rotation of the forearm so that the palm is facing posteriorly or inferiorly (i.e. backward or downward)."

- The Oxford Dictionary of Sports Science & Medicine "Pronation"

Tennis instruction is mired in a linear conception of tennis. We say to take the racket "straight" back. We say to "finish out towards the target". On the serve we say to "drop the racket in a backscratch postion and swing up to contact and snap downward" (linear drop followed by a linear upward path) and that power comes from a "downward snap" of the wrist (linear movement downward). At the core of these linear concepts is a conception of tennis that goes in a straight line - from takeback point A to finish point B.

 Becker is pronating his forearm arm and hand into contact.
The huge problem here is that human joints and muscles and tendons don't move very well or very quickly in straight paths. Our bodies move most naturally, most powerfully, and most rapidly through rotational motions. So this linear approach to tennis that most teaching pros offer results in movements that are unnatural and ineffective. They lead to stilted, long, linear strokes that result in little power, little connection with the ball, and almost no integration of the body into the stroke. And that is why people who take lessons are so frequently stuck at awkward low levels - often for their entire lives.

 Frank Dancevic applies a torque to the ball by rotating his forearm clockwise as he pushes forward and lifts upward from the shoulder.
In my high speed footage (and even in the 60fps footage) you will see rotation, angular momentum, and torque occuring in all the strokes. We see the torso rotating 90 degrees or more into the ball on the forehand. We see the rainbow like path of the full windshield wiper motion on the forehand. We see the arm and hand twisting a full 180 degrees on the serve. We see the entire arm start to rotate from contact on in the one handed and two handed backhands. On the forehand volley we see the entire arm - from hand to shoulder - rotate inward from contact on. On all the ground strokes we see an "inside out" path of the racket into contact which generates angular momentum. This list goes on.

For a quick look at rotation, torques, and angular momentum in all the strokes, let's start with the serve - the most remarkable example of rotation and torque you can find in our game.

Next: The Serve

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Rotating motions, angular momentum, and pronation - hidden secrets of the professional game.
A combination of twisting and pronation accounts for the kick serve (seen here) and the big first serve.
Federer pronates with his forearm to generate a huge first serve.