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Old 01-22-2013, 06:40 AM   #132
Chas Tennis
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Join Date: Feb 2011
Location: Baltimore, MD
Posts: 4,119

Originally Posted by treblings View Post
.......................power comes mainly from the large muscle groups. but are you saying, that there is no active forearm and wrist pronation? that it happens automatically with no intent from the player? and is something of a byproduct?
I don't think as much in terms of power, which is a difficult thing to estimate as each phase of the serve occurs. The question of which muscles provide the most 'power' overall to the serve is important but the details are more useful to focus on. I think more in terms of specific joints, attached muscles, velocity and a specific phase of the serve. Most important is the last phase just before impact and its racket head speed. At that time, some muscles have been pre-stretched and are shortening rapidly to act through the hand to give the final racket head speed the instant before impact. Looking back into the earlier serve motion phases in videos, you can clearly identify some of the motions that stretched the specific muscles, for example, lat stretch from leg thrust. There are other motions that involve the trunk and shoulders that probably produce stretch but are more difficult to observe in video and understand. I am now trying to see the supination and pronation earlier in the motion discussed in another thread. [Supination stretches the pronation muscles.]

Term Usage - I am using the term pronation to mean motion in that forearm rotation direction and not joint position. The usage - for position or location - is ambiguous. I have seen forum discussions where one party was talking position and another was talking location. Search - pronation in anatomy usage and usually the word means location and not a rotating motion. On this forum it usually means a rotating motion. The overall arm rotation rate at the wrist is the sum of the internal shoulder rotation and pronation angular rotation rates.

I saw a graph that showed pronation rates: 1)some pronation earlier in the serve motion and 2) a lot of pronation later, after impact, but 3) not very much pronation rotation rate at impact. In video, I can see the large pronation following impact but I can't distinguish the smaller pronation and supination earlier in the motion, too confusing, also elbow and wrist angles are too difficult to see without markers. I believe that both pronation and supination are important. I believe that strong serves probably have little conscious active pronation the instant before impact and give the arm a relaxed feeling. I have hit a very small percent of serves with a 'relaxed' arm and have gotten strong serves doing it. But that is not my normal match serve which has some tightness.

Speculation: In a powerful serve it may be physically impossible for the small pronation muscles to pronate the arm & racket just before impact because the powerful ISR muscles are already angularly accelerating the arm & racket so forcefully. ? Similarly, you can't jump up in a rocket ship accelerating at 4 G's, you would be hard pressed in your seat.

Research: Elliott, I believe, has said that pronation functions to orient the racket face and that ISR provides the largest contribution to racket head speed. I believe that practicing the serve is training including to reproduce a certain degree of pronation for racket face string direction at impact.

Active & Passive Muscle Shortening and Sensations/Feelings - When you walk your muscles are actively and passively shortening to supply forces. I believe that the passive shortening from pre-stretch muscle has little feeling of effort, relaxed. Also, for the active component of muscle shortening, because we are so well trained at walking we don't/hardly consciously/deliberately notice that we are sending nerve impulses (EMG signals) to the legs. If you are trained for the serve do you 'consciously' send nerve signals to muscles, probably not, especially since there are 600 muscles in the body and many are involved in the serve? It would be nice to find some research clarifying the feelings for active and passive muscle shortening. It might explain what a 'relaxed arm' is, what 'muscling the ball' is - in terms of muscle theory passive & active muscle shortening and sensations. When I completely 'relax' my serving arm and don't 'muscle the ball' am I using mostly passive pre-stretched muscle shortening to hit the serve?

Last edited by Chas Tennis; 01-22-2013 at 07:10 AM.
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