Chas Tennis
G.O.A.T.
If there is a rotation axis and an object is rotating around that axis,
the speed of the object is
r (radius) X rotation rate
Where the radius is found by first finding and drawing the axis, including extending the axis beyond the object. Then you just draw (or imagine) the radius perpendicular to the rotation axis. Much of racket head speed in tennis strokes is produced by an object rotating around one or more axes. The object may be above or below the body part with the axis, but still the important thing for speed is that same r, measured perpendicular to the rotation axis.
Frequent rotation axes for ground strokes are the
Spine (observe the line between the two shoulder)
Shoulder Joint (observe the upper arm)
Elbow
Wrist (observe the racket shaft)
These axes can be used together or sequentially, one after the other. For ground strokes, often the forward swing starts with spine rotation & its axis and then the shoulder rotation & its axis occurs with timing that can be clearly seen in high speed videos. The spinal rotation is usually the most significant for building racket head speed, it rotates the entire shoulder joint. For stroke details look at high speed videos.
Rec players typically use more shoulder and less spine for their ground strokes. They may not be clear about their main rotation axis and they may not be aware of the distance from their racket head to an important rotation axis.
Determine your main rotation axes that provide the most speed for your strokes. Observe the timing and racket positions for each axis in ATP and WTA ground strokes.
Remember that if you bring the racket head or some body part closer to a rotation axis, it will not pick up as much speed from the rotation. Notice that the pros don't bring the racket head close to their rotation axes and the rec players may.
This detailed post compares a pro player, Gasquet, and Mojo28 frame-by-frame. Note - the rotation axis through the neck area for Gasquet and the racket head's distance from the rotation axis.
What do you think about rotation axes?
the speed of the object is
r (radius) X rotation rate
Where the radius is found by first finding and drawing the axis, including extending the axis beyond the object. Then you just draw (or imagine) the radius perpendicular to the rotation axis. Much of racket head speed in tennis strokes is produced by an object rotating around one or more axes. The object may be above or below the body part with the axis, but still the important thing for speed is that same r, measured perpendicular to the rotation axis.
Frequent rotation axes for ground strokes are the
Spine (observe the line between the two shoulder)
Shoulder Joint (observe the upper arm)
Elbow
Wrist (observe the racket shaft)
These axes can be used together or sequentially, one after the other. For ground strokes, often the forward swing starts with spine rotation & its axis and then the shoulder rotation & its axis occurs with timing that can be clearly seen in high speed videos. The spinal rotation is usually the most significant for building racket head speed, it rotates the entire shoulder joint. For stroke details look at high speed videos.
Rec players typically use more shoulder and less spine for their ground strokes. They may not be clear about their main rotation axis and they may not be aware of the distance from their racket head to an important rotation axis.
Determine your main rotation axes that provide the most speed for your strokes. Observe the timing and racket positions for each axis in ATP and WTA ground strokes.
Remember that if you bring the racket head or some body part closer to a rotation axis, it will not pick up as much speed from the rotation. Notice that the pros don't bring the racket head close to their rotation axes and the rec players may.
This detailed post compares a pro player, Gasquet, and Mojo28 frame-by-frame. Note - the rotation axis through the neck area for Gasquet and the racket head's distance from the rotation axis.
This post from another thread shows a comparison and analysis of poster Mojo28's one hand backhand drive and Gasquet's from the start of the forward racket motion. Note the chest and upper arm of the high level backhand.
[ Note for new readers - It is necessary for this analysis to understand the defined joint motions of internal shoulder rotation (ISR) and external shoulder rotation (ESR). The upper arm between the shoulder joint and elbow does not go anywhere, it just spins like a top around the upper arm's center line.]
Pictures of each frame of Mojo's video. The time scales are in milliseconds with "0" milliseconds being impact. -267 milliseconds is about 1/4 second before impact.
I point out differences between better high level strokes and the poster's strokes. A poster can select a high level stroke and copy it or use some other stroke model. Or, go with instruction or on their own without a model or instruction.
Mojo's ball is lower than Gasquet's. Compare similar ball heights for better analysis.
Frame at -267 ms. It looks as if at 267 milliseconds before impact the OP has turned his shoulders back to about the same angle as Gasquet has. Compare also shoulder turn angles at impact, at Frame -0 ms. The positions of the arms and rackets are different. Gasquet's racket has not come down and is still in front of his body. Is Mojo copying some other backhand stroke? Mojo has also done pronation to bring the racket down. Impression is that Mojo is doing his own thing. ? (To see angles more accurately, the cameras for both backhands need to view the players and courts from the same angle. Wear tight fitting clothes or a short sleeve shirt to better see the upper arm, elbow angle, etc.)
Frame at -233 ms. Mojo has brought his racket farther down. Gasquet's racket has gone up slightly. Mojo's elbow looks bent more and his upper arm (between the shoulder and elbow) has more downward rotation (ISR). Compare ISR angle to ISR angle as these frames progress.
Frame at -200 ms. Mojo's racket is still lowering and low. Gasquet's is just starting to lower.
Frame at -167 ms. Mojo's upper arm is down from the shoulder joint. Gasquet's upper arm is more across the chest.
Frame at -133 ms. Mojo's racket still lowering. Gasquet's now lowering with more rapid drop.
Frame at -100 ms. Mojo's upper arm is down at the chest. Gasquet's upper arm is more across the chest. Gasquet now appears to have started more upper body turn. I believe that to produce this early arm and racket acceleration that Gasquet is pressing hard on his upper arm with his chest powered by the forces of turning his upper body. If a credit card were between his chest and upper arm, would it be pressed tightly? How much upper arm pressing Mojo is doing this is not clear (due to the obscuring shirt and arm angle). But his upper body does not appear to be turning as rapidly.
Frame at -67 ms. The racket head speed developed by any rotation depends on the location of the axis of rotation and the distance out from that rotation axis. Look at the arm and racket angle and the distance out from the location of the rotation axis (guessed for now). It looks as if Mojo's arm angle is not favorable for racket head speed. Also, Mojo's racket is already much more rotated toward the ball trajectory. Gasquet's racket is >180° back from the ball's trajectory. Gasquet's upper arm is pressed to his chest as discussed.
Frame at -33 ms. Look at the racket to ball trajectory angle for Mojo, 45°? Look at the racket to trajectory angle for Gasquet still >180°. The total turns of Mojo's and Gasquet's upper bodies from Frame -267 ms seem somewhat similar, similar average speeds. The upper arm and racket have been used differently. Another motion - now look at the elbow bones and estimate the angular position of internal shoulder rotation, or axial rotation of the upper arm in the shoulder joint. Compare ESR from -33 ms to -0 ms.
Frame at -0 ms closest to impact. The big differences from Frame -33 ms to Frame -0 ms are the angular movement of Gasquet's racket and the much larger movement of his hand in the forward direction in comparison to Mojo. Also, Mojo's racket is open and Gasquet's is closed at impact. Possibly the ball height was a factor in how closed the racket was.? Now look at Gasquet's elbow bones and compare them to Frame -33 ms. Gasquet has done rapid external shoulder rotation (ESR) from Frame -33 ms to Frame -0 ms. That has moved the racket up and added to the topspin that the upward hand path already would have produce without ESR. Because Gasquet brought down his racket earlier with a near straight arm, it caused rapid ISR and pre-stretched his ESR muscles, he is using those stretched muscles in this frame. (Search the Stretch Shorten Cycle).
Frame at +33ms after impact. Mojo's hand and racket go more forward. Gasquet's goes more forward and up. ESR has continued.
Frame at +67 ms. Comparison of the follow throughs.
Video.
Last edited: Mar 5, 2017"
What do you think about rotation axes?
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