Seriously About Pronation and Kick Serve #1

[toly]

Originally Posted by LeeD

Well, certainly makes sense, how can you pronate with any added speed if your racket is aligned with your forearm?
McEnroe might argue, but his serve, being great with the wide slice, is not nearly fast compared to every other player of his era.
High strikepoint is all nice and cozy, but being able to hit a fast ball with heavy pronation is more important.

What happened to you LeeD? Incredibly, you begin praising pronation!

[stormholloway]

This is what I'm trying to work on at the moment. I get that the kick serve is like a "throw" across the ball and to the side rather than a "throw" into the court, but I just can't seem to time pronation properly.

[charliefedererer]

Originally Posted by toly

This is Jim McLennan from tennisone.com. I saw these videos many times. But, thank you anyway. He preaches the same idea (arm pronation) as I do. But, I don’t like his explanations.
He says, if we have racquet off line with forehand we can increase the leverage and force. It could be true, if we were able to apply our left arm to racket tip, then we would increase leverage and force. Unfortunately, we cannot do that. But, we can increase radius RH by increasing beta angle.

I don't like the term "leverage" that Jim McLennan uses here, and Pat Dogherty (the Bollitieri "Serve Doctor") uses in his videos. "Pronation" seems like a better overall description of the motion taking place (even though it is a combination of pronation at the foream and internal rotation at the shoulder.)

But it was Systemic Anomaly that pointed out that the term "lever" is technically correct if you consider the action at the elbow as a third class lever, with the force between the fulcrum [at the elbow] and the distal load [the racquet].
"Your arm (fig. 1-6) is a third-class lever. It is this lever action that makes it possible for you to flex your arms so quickly. Your elbow is the fulcrum. Your biceps muscle, which ties onto your forearm about an inch below the elbow, applies the effort; your hand is the resistance, located about 18 inches from the fulcrum. In the split second it takes your biceps muscle to contract an inch, your hand has moved through an 18-inch arc. You know from experience that it takes a big pull at E to overcome a relatively small resistance at R. Just to experience this principle, try closing a door by pushing on it about 3 or 4 inches from the hinges (fulcrum). The moral is, you don’t use third-class levers to do heavy jobs; you use them to gain speed."
- http://www.tpub.com/content/engine/1...s/14037_13.htm
(Of course during the serve, it is the triceps extension at the elbow that is the third class lever action.)

So perhaps the use of the term "leverage" actually does explain the principle force/speed generated in the arm during the serve. The last bit of pronation at the end merely redirects the vector of the force.

[toly]

Originally Posted by charliefedererer

But it was Systemic Anomaly that pointed out that the term "lever" is technically correct if you consider the action at the elbow as a third class lever, with the force between the fulcrum [at the elbow] and the distal load [the racquet].
So perhaps the use of the term "leverage" actually does explain the principle force/speed generated in the arm during the serve. The last bit of pronation at the end merely redirects the vector of the force.

The arm pronation rotates the racquet in horizontal plane; hence the gravity is not important. In this case we cannot use directly first-class lever etc model. But, to simplify the matter, let assume the racquet’s inertia behave like gravity force (load). Figure 1 and figure 2 demonstrate the hand’s functions, while pronation beta angle is 90°.

Figure 1
The part of the hand around index finger creates force F1. The pinky could be some kind of fulcrum. It would be like third-class lever. The force F1 generates torque T = F1*D, where D is the size of hand , see fig. 1. To increase D, and thus torque, a lot of tennis players spread their fingers.


Moreover, the hand around pinky is also able to exert force F2, see figure 2.

Figure 2
The index finger would be fulcrum. The hand works like first-class lever and creates torque T2 = F2*D. Torques T1 and T2 would rotate the racquet in horizontal plane.
If pronation beta angle equal zero, the hand can treat the racquet handle as well as the handle of the screwdriver only. The racquet handle diameter (d) is usually much less than the size of the hand with spread fingers (D). And hence, the hand produces much less torque than in case as beta = 90°.
if the beta angle is any value between 0° and 90°, then the torque can be calculated according to formula T =F((D-d)sin(β) +d).

[charliefedererer]

^^^I'm not sure why you chose to emphasize the the lever action at the wrist in your most recent post.

While salsinglesa makes an important point in his last point in a concurrent thread on levers ( http://tt.tennis-warehouse.com/showthread.php?t=361952 ) I thought from the illustration provided that the most obvious lever in the serve concerning pronation was at the elbow, with the foream, hand and racquet essentially acting as a unit distal to the fulcrum at the elbow.

The somewhat less obvious, but very important lever for "pronation" (anatomically correct term of internal rotation) is at the shoulder.

The wrist does go from extended to neutral, and there is ulnar deviation, but the "wrist action" contributes relatively little to the force of pronating and hitting the ball.

But yes, action of multiple levers at the wrist, elbow, shoulder, spine, hips, knees and ankles all contribute to the multiple stage catapult making up the kinetic chain.