OOAK Table Tennis Forum

The function of feedback in blades.

Feedback in blades is referred to as “feel” or “touch” and sometimes more directly as “flexibility”. It is often suggested that flexible blades with a good feel or touch will make it easier to hit the ball just right, improving the quality of your strokes - and they do, but still the matter is not as simple as that.
“Feel”or “touch” is what the muscles and nerves in a hand holding the grip of a bat sense of the vibrations in the blade’s head caused by the impact of the ball when it is in contact with the rubber. These vibrations convey information about speed and spin of the ball – the incoming speed and spin as well as the speed and spin which are a result of making the stroke. Speed is felt as intensity of the vibrations. Spin is felt as quality of the vibrations – a ball will feel “heavy” if there is a lot of spin on it, and the way the vibrations change when contacting the rubber will make you feel e.g. whether or not you are putting good spin on the ball, or whether or not you have made the pips of your LP rubber bend.
Feedback actually is there when the vibrations in the blade’s head are transferred to the hand and processed by the brain. The time during which the ball is “on” the blade – or more precisely, is making contact with the rubber – is approximately a thousandth of a second. In contrast, the nerves and the brain need tenths of seconds to process the information felt by the hand and to respond to it. Time, therefore, is far too short to adjust flaws in handling the ball during the interval the ball is on the blade; if you don’t hit the ball just right, there is nothing you can do about it while you are actually hitting it. However, the information processed by the brain is retained; as such it can be used, first, to help interpret the effectiveness of the stroke (feeling adds information to what you see) and, second, to make adjustments the next time you hit the ball. So, “feel” and hence feedback are not functional immediately, but indirectly.
The good feedback can do a player is then, first, helping him to know how well he hit the ball. This is important tactically, for it helps to decide what to expect from the opponent and how to anticipate on his most likely reaction. Visual information is often not enough to decide this: it is difficult to see how much spin and speed there is on the ball. If, however, you can feel spin and speed, you will far better be able to judge the quality of your stroke and the degree of difficulty the opponent will have handling the ball as a result of it, and from that to decide what to expect and how to anticipate it.
Secondly, a player can benefit from feedback because it is extremely helpful in the learning process. Learning how to perform strokes well using only visual information (the trajectory of the ball, if and how it clears the net, where it lands, how it behaves when contacting the opponents bat) is difficult and comes slowly, because the information is not directly linked to what the muscles do. Feeling how you perform the stroke and handle the ball, by feeling the vibrations in the blade and interpreting them, will train the muscles directly. Muscle-memory is subconscious, you are not directly aware of it, but it is there determining your reflexes; that makes it very important in table-tennis. Feeling the vibrations will also add to your general knowledge of the behaviour of the ball as a result of your strokes; this knowledge is a part of the conscious learning-process.
As feedback is important, so is the ability of the blade to generate vibration and transfer it to the grip. The construction of blades may either maximize or minimize this ability. As for the head, vibration will be less and more complex with every ply added. Single-ply blades have optimal vibration – if the wood they are made of vibrates well. The best wood comes from needle-leaved trees; musical instruments are nearly always built from it. A Stradivarius violin is, as it were, a single-ply Hinoki blade. Multiple plies will dampen vibration and/or make it more complex (as every layer has its own vibrations), but this can be (partly) compensated by gluing techniques, choosing woods that combine well, making the plies thin, and so on. Generally, a blade that is flexible will vibrate well. To have good feedback, however, the vibrations have to be felt in the hand, so the vibrations must be transferred to the grip. Several blade-designs purposely prevent this by putting dampening layers between the grip and the wood of the head in some way. Most designs do not prevent it, but do not purposefully improve transference either. Only one design (as far as I know) aims at maximizing transference of vibrations from the head to the grip, and this is patented by Re-Impact. It does make these blades unique.
Transference of vibrations is also dampened by the rubbers on the blade; the thicker, the more. Therefore it makes very good sense to have especially younger players use thin sponge; this will speed up their development. Feedback is especially important too in defensive and all-round playing-styles, as manipulation of spin and speed is essential to them. Blockers also benefit from good feedback. These players will be best off using blades that vibrate well and transfer the vibration the grip. Hitters and quick attackers have less practical need of it.

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Fascinating study and article Kees!

I can't help but question the bit about us not being able to adjust a stroke on contact, because the brain cannot process it in time. It feel like it can for brush strokes, or for slower controlled strokes. For example with a slow and spinny control rubber, it feels like the ball is so long on the bat, that you have the time to guide it to the position you want. Of course I only know it 'feels' that way, and this does not mean that it's actually happens. Is it possible that for these much slower control and brush strokes, the ball IS actually long enough on the bat to make an adjustment?

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Great article Kees. Well written and interesting. I think I knew everything you wrote, but reading it is like a "meeting of the minds" in confirming knowledge. Its not something you do think about a lot when playing the game, it comes so much as second nature. I do think the length of time the ball is on the rubber varies between what shot is hit and what type of rubber is being referred to. I don't know any way you could measure the time under varying conditions, but it would be great to know.

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Haqggisv wrote: According to physics and psychology (or neurology, really) it isn't. You may have the impression you can do it, but the mind is a trickster... Try to do it the next time you play and you will probably find that adjustments you make are actually coming after the ball has left the blade well and good. Actually you can see that happen a lot, people making awkward jerks at the end of a stroke, without any actual result (quite often the ball has cleared the net by then already), but reacting to the feedback, knwoing they have made a mistake.

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Thank you, Kees.

That is very well written and clearly by a master of blade understanding!, every table tennis player should read that. It's hard for learners to understand how a flexible blade with good feedback helps you improve your game faster but if everyone could read that it would make more sense to them. Any time you are in a developmental stage of your table tennis you _need_ a blade like that no matter the level you are at. I think I'll vote that to be a sticky somewhere on the site

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Cool !
Thanks for the share Sir Kees !

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Thanks kees. This is a must read

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Enjoy the game. It is a never ending learning experience once you play and keep the ball on that 45 sq ft of space or should I say half of that space.

I've stickied the topic, and it's a great post and definitely worth further discusion

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It must be noticed that the more vibrations the less is sweet spot. Hitting out of sweet spot may be used by some playing styles for spin and speed variations, but may detriment the control of the racket by learning players. So there is balance between feedback and precision.

Omut wrote: Vibrating of the wood isn't the same as swinging or deforming; a blade's head may swing on impact, meaning that it is moving independently from the grip and/or that its surface is deformed (rippling, bending); vibration means that there is a complex wave (like a soundwave) moving through the whole of the wood without deforming it. Vibration doesn't, therefore, decrease the sweet-spot of a blade. Swinging/deforming does. Compare it to a string on a violin - if the string is tensioned well (hence is "firm") it will vibrate producing a clear sound; if it is tensioned weakly ("infirm", like a wood which is too bendy) it will just produce noise. Tension in the wood of a blade is made by choosing woods with good grain (which can be heard when knocking on it) and glue them together in exactly the right way using a glue that will not hinder the wave. A well-vibrating blade will be very precise; more so than a non-vibrating blade, even if the latter is very rigid and un-flexy.

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Can you give me the specifics of physics and neurology? What's the dwell time and what's the speed of a well-honed reflex? I find the "awkward jerks" to work pretty often, and the more dwell the setup I have the better it works. I'm sure 99% of the "jerk" is just the follow through, but that 1% of it that happens while the bat is still in contact with the ball, if it happens in time, does seem to work.

Dwell-time of the ball is around 0.002 sec, a reflex reaction takes about 0.18 sec (from the point in time when a visual stimulus is transported to the brain till the point in time the muscles start to contract), but near 0.14 sec when based on audio input only (that's why in the 1970's Japanese attackers started to train blindfolded, because hearing the sound of the ball on their opponent's bats they would know what to expect and thus be able to react quicker). There are other types of physical (and mental) reflex, but table-tennis reflexes are dominated by visual input (that is e.g. why lots of players will push reacting on seeing a pushing motion of the opponent, even if they know he is playing with LP or anti). So adjusting reaction while the ball is on the blade is out, but you might be able to adjust your stroke before contact and as it all happens very fast this might feel as if the adjustment was made on contact.

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Does a pull-back block increase dwell time?

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Here is something that will give you a good idea of how fast 1/1000 second is. This man holds the world record for drawing a pistol. It takes him .145 seconds to react to the signal and less time to make the draw! Since the ball is on the bat less than .004 and probably less than .001, any correction is being made before or after the contact. Those wild changes at the end of a stroke could have started well before contact was made when your brain sensed it needed a correction.

http://www.fastdraw.org/fd_draw.html

Gary Moore used to have a TV show and had the old world record holder on the show. He had Gary hold his hands 8 inches apart. When a light came on, all he had to do was close his hands togather. The guy with the gun stood faceing him. He had to draw the gun and put it between his hands before Gary could close them. Gary lost Every time!

Drag racers typically break the start light by a few 1/1000s of a second but they are not reacting to a single light. They have three light in a row and are "timing" release of the clutch based on the sequence of the lights.