Soderling's Backhand; Video Available?

[BrianGordon]

You supported the idea that your work was on topic in the discussion of elite pro servers vs avg pro servers. Thru doing this, you are saying that your methodology and data were proper for that topic. I find that very questionable, don't you? -no?

You cut off the next statement which is why I believe my research gives insight into serving at any level - so while it is not my intent to explain all the intricacies of Pete's serve formally (even though his data is in my set) if it comes up in an informal forum I'll state my opinion based on that belief - you disagree - others can make up their own mind.

If all you are looking at, as you state,
is racket head velocity to be elite,
then I must question that as well. I think they need to be able to find the svc box with 135+ mph ball speed, with a stroke that holds up in a world class event. Some guy who can sling a racket at high speed for maybe a mishit into the back of the fence won't qualify for me.
Methodology -no?

Wow - I never thought of that - thanks.


Look - I get it - you've made it quite clear you despise my pompous *ss and think my work, and that of the field, is a hunk of garbage. I'll just have to live with that reality - now if you don't mind, I'm done with this thread.

[airforce1]

To Airforce:

You did not answer the question – methodology is the way in which we acquire 3D data and the techniques used to calculate the mechanical parameters. Using my new technology as an example, you might say that because it is only capable of measuring at 720 frames/second it is too slow to capture the subtleties of a fast swing. You might say that its 1/10 millimeter accuracy represents far too much measurement error. Or that the placement of the anterior marker proximal to the elbow accounts for 1 degree of rotational error in determining the twist orientation of the humerus – those are answers to the question.

Instead your answer seems to be that my goal is to extrapolate my data to explain pro mechanics. Clearly this is not my intent here or in academics. And I’m not sure where you get that because my series here is about how we use 3D in junior player development. I necessarily explain some mechanical concepts based on findings of higher level players and where I thought it added something interesting, I related a few of those concepts to things you can see on John’s pro video.

I guess we will always disagree because this seems to offend your vision of what “elite” players do. But I work specifically in stroke mechanics where elite is not a ranking but rather based objectively on ones ability to generate racquet head velocity.

You supported the idea that your work was on topic in the discussion of elite pro servers vs avg pro servers. Thru doing this, you are saying that your methodology and data were proper for that topic. I find that very questionable, don't you? -no?

If all you are looking at, as you state,
is racket head velocity to be elite,
then I must question that as well. I think they need to be able to find the svc box with 135+ mph ball speed, with a stroke that holds up in a world class event. Some guy who can sling a racket at high speed for maybe a mishit into the back of the fence won't qualify for me.
Methodology -no?

[BrianGordon]

To Airforce:

You did not answer the question – methodology is the way in which we acquire 3D data and the techniques used to calculate the mechanical parameters. Using my new technology as an example, you might say that because it is only capable of measuring at 720 frames/second it is too slow to capture the subtleties of a fast swing. You might say that its 1/10 millimeter accuracy represents far too much measurement error. Or that the placement of the anterior marker proximal to the elbow accounts for 1 degree of rotational error in determining the twist orientation of the humerus – those are answers to the question.

Instead your answer seems to be that my goal is to extrapolate my data to explain pro mechanics. Clearly this is not my intent here or in academics. And I’m not sure where you get that because my series here is about how we use 3D in junior player development. I necessarily explain some mechanical concepts based on findings of higher level players and where I thought it added something interesting, I related a few of those concepts to things you can see on John’s pro video.

I guess we will always disagree because this seems to offend your vision of what “elite” players do. But I work specifically in stroke mechanics where elite is not a ranking but rather based objectively on ones ability to generate racquet head velocity. And, in fact, the higher level players for which I have data generate as much and usually more racquet head velocity than quantified values published, or that I have found myself, for pro players. I don’t claim my work provides all the answers yet, but it gets us closer by the day and but for people like you, I so far have enjoyed giving players and coaches access to information they otherwise would find hard to access.

To Adam:

You did nothing to cause this – I like your insight and while I don’t always agree, you have come up with a gem or two. There was a master’s thesis done in my lab last year that investigated different types of martial arts punches – hand velocity, impact impulse, etc. as I recall. I don’t believe it has been published but I would be willing to copy some of it and send it to you if you PM me – believe it would be right in your wheel house (so to speak).

To Crass:

Actually it seems to me that you have thought about this a lot but that your choice to explain the concepts with mechanical terminology probably masks your insight and/or meaning. The speed of the racquet at contact is related to the angular momentum of the racquet about the body center of mass (primarily about a vertical axis on ground strokes).

This angular momentum is developed in the racquet by first developing angular momentum in the entire body by pushing against the ground to elicit a horizontal ground reaction force – if this force is eccentric to the body center of mass it will cause rotation of the entire body – the eccentric (off center) force is referred to as the moment of the force or sometimes a torque.

The degree to which this torque angularly accelerates the body is dependent on the moment of inertia (I) by torque = I x angular acceleration. Those of heavier stature will have a bigger I about the axis in question – requiring proportionally greater torque to attain the same angular acceleration. The torque will over time (angular impulse) cause the body angular momentum to increase and it can then be transferred through the body to the racquet.

The transfer is accomplished via the joints using joint torques and forces and action/reaction. Assuming the that a heavier person is proportionally larger across the board then the transfer at the joints requires more joint torque and force to attain the same acceleration and angular acceleration at each segment in the chain. I believe this is why one typically sees athletes, for which the velocity of distal endpoint (racquet) is a priority, possess long/lean segments rather than massive ones.

Therefore, heavier folks will need to be proportionally stronger and work harder to attain the same racquet speed. So… if it is your contention that more weight implies more strength and fitness to the extent that one can repeatedly overcome the inherent inertial resistance to attain greater acceleration for the body and at each link in the chain then your theory holds – this is not what you seem to be saying, however.

[crass_lawner]

Einstein never confused mass with weight, speed with acceleration, associated f=ma with rotational motion, described mass and speed as transferable forms of energy, abstracted the kinetic chain into nothingness, or considered weight transfer a mechanical concept, to name a few.

Sorry, like I said, I haven't devoted my life to physics so I got some of the wording wrong, but Mr. Gordon if the basic idea of what I'm saying is so preposterous, could you please explain one simple thing to me? If the force that a tennis player exerts on a tennis ball isn't predominantly a result of them transferring their weight into the racket, then where does it come from? Surely the racket velocity times the weight of the racket and the arm alone would not be enough to propel a tennis ball very far, so where does this mystery factor come from?

Also the latter part of your thread makes it sound like you assume that when I say a player "puts their weight into the ball" I mean in a linear forward motion, but I fully recognize that groundstrokes are mostly a result of rotational motion. But a player can still create rotational force with their bodyweight, which can then be transferred to the racket. I don't see anything mysterious about that.

[johnyandell]

OK it's official. This has sunk to the level of some of the debates at Tennis Warehouse, where I confess, I at times was a ringleader.

And I probably got it started with my responses to Gmann and Crass. I see a lot of things, not just here, but in my travels and speaking and interaction with coaches at all levels, in which people claim things that are contradicted by known and well established opinion--and I should probably just let that lie sometimes, instead of raining on people's parades.

As for the rest of you:

Air Force you should be ashamed of thst last long post! Biomechanics is a better established science than say economics. Brian studied with one of the top guys in the world, and the phd's at the USTA praise him. We should thank god he is studying tennis. The methodology is here to stay--and what he is about to do is going to bring a wider application to it than anything previous. You can disagree with him but to make facile comments about how this type of work will crumble, well, that is just ridiculous.

Crass, stick with your opinion and that's fine--you should just know that the preponderance of the research says something else, and maybe that is something you should look into or at least address.

Adam, yeah don't freak out.

Hey we are hopefully on the edge of seeing something that really matters tomorrow morning start 6am pdt. Go Roger and may god bless his French title. We can dissect Soderling's strokes later.

[oliensis]

One more annoying remark, for anyone who's not utterly over this subject:

I've been punched by a very fast jab that had no penetrating power.

Contrawise, I've been punched by a very slow, short hook that made me feel like my liver and spleen were being deeply and permanently dented.

The jab clearly decelerated upon impact, where the hook decelerated much less, delivering what, in Tae Kwon Do, we call "shuddering force" deep into my thorax.

WHY did the jab decelerate on impact so that my face did not distort much, where the hook decelerated so much less, distorting my rib-cage and hurting me deeply?

Both blows were delivered by "racquets" (fists) that had very similar masses. But were the hitting levers of such similar masses? For any number of reasons, I continue to suspec not.

In case those with actual quantitative knowledge can translate what I'm talking about into the terms in which their models understand the variation in deceleration on impact, I'd be very interested.

If this subject has become too much of a nuisance, so be it.

Again, with good will toward all...and especially toward the curious.

Adam Oliensis

[oliensis]

I, for one, offer sincere regrets that this thread has become so conentious (not intellectually contentious, that's good in my mind, but personally contentious). And to whatever extent any remarks I've made have contributed to ill will, I offer my apologies.

This is a subject that's been on my mind off and on, as I said, for almost 30 years. And I've never had a discussion about it with anyone, least of all with people who are knowledgeable on important aspects of the subject, such as John Yandell and Brian Gordon.

The following text, quoted from Brian Gordon, offers the kind of food for thought that I genuinely appreciate.

To the point of at least the latter part of this thread, getting the weight behind the ball or transferring weight into the ball is a coaching concept. The mechanical concept is motion of the center of mass and associated linear momentum. In both cases the impact on racquet speed (shot power) at contact is so negligible I don’t even report it when assessing contributions to racquet head velocity on ground strokes.

This makes sense intuitively on a backhand (primarily neutral/square/closed stance) stroke where the contact of the front foot on the ground and impending leg drive, near the end of the backswing and during the forward swing respectively, serve to stop any forward linear momentum of the body. This is by design to generate angular momentum for the body.

The case put forth by oliensis of effective mass is more compelling but really just represents different system definitions. Differences in speed of the end point across different techniques in the examples cited will be due to a combination of altered range of motion, altered joint rotation contributions, altered muscle moment arms and associated muscle lengths, and changes in the velocity of muscular contraction needed to rotate the joints among others. The primary difference between a straight arm forehand and the double bend for example, is not one of effective mass, but rather one due to alteration of the way upper arm rotations contribute to racquet velocity and what that means for other joint rotations.

Finally, if the velocity of the body center of mass is linked to a large proportion of the racquet head velocity, as on a classical volley due to minimal joint motion, getting “the weight” behind the ball can be important to racquet speed at contact – so I guess it is no coincidence that the timing of the step with the front leg relative to contact is radically different than on a ground stroke.

Thanks for this input and to all for other input like it. It certainly gives me food for thought.

(My remark about double-bend vs. straight-arm forehand was just a stray thought/question without great conviction, one which I can easily see your point on. However, I have trouble letting go of the notion that mass is important in the phycis of all this, but that doesn't mean that I shouldn't let go of it...or that I will or won't be able to.

The "ballistic" battering ram on roughly a "swing" contraption continues to be a powerful metaphor for me, and in that one, it's clear that the mass of the battering ram plays at least a somewhat significant role in the force it can deliver.

My regrets if my relatively crude physics education and practical martial arts experience make me too intellectually clumsy to let go of my intuitive senses of things. But, I do agree with the poster who suggested that imagining things out (thought experiments) is how many (not all) good scientific hypotheses are generated, which are subsequently tested and either proven or debunked.

With good will toward all.

Adam Oliensis

[airforce1]

Appreciate the psychological profile - but I really only had one question for you - your answer had nothing to do with it though I understand it was easier to attack its genesis - if you question the methods of, if not me, the discipline then state your case - clearly you have done a lot of research to form this option - to question the legitimacy of an entire scientific field deserves at least that - no?.

Actually my answer went directly to the heart of your question. The fact that you missed that explains a lot, or it is entirely possible that I didn't express myself very clearly. Either way, I didn't attack anything, only pointed out the flaw in the process.

I provided a specific example of how having measured and collected data, means next to nothing if you attempt to relate that data improperly.

and of course there is this quote-
"Data do not imply their own explanation." The ability to measure and calculate millions of numbers will not further the understanding of tennis strokes. Biomechanics alone is not the holy grail of sport understanding, and there are some issues the current methods of biomechanics can't address.
It's also important to understand that biomechanical analysis itself is subject to a degree of error

I thought that was well stated.

[crass_lawner]

Hmm well this discussion has gotten interesting, and it's good that there are others out there who care about this stuff. I did feel like my ideas were pretty much disrespected by John, but that's not that big a deal I'm used to it and pretty much expected it to happen at some point. That's what happens when you try to discuss something new and/or abstract. Although not perfect, at least this discussion (not just my part of it) has already progressed much more than it would have on any other tennis forum that I'm aware of.

To tell you the truth, I don't have any advanced degrees in anything, but have taken elementary physics and am a player (with a 2hbh) and a fan of tennis. But I really don't think that anything I've talked about requires anything beyond elementary physics to understand. And I'm sure that in some of my posts I've made technical errors that are horrible and unforgivable to someone who knows a lot about physics (Brian Gordon). But even so I think my basic premise is sound: That a player with good technique can successfully transfer their bodyweight into their racket and eventually the ball. Especially on the 2hbh because the levers (arms) are shorter there and the movement (or acceleration or whatever) is more linear (forward) than on the forehand. This is like on the volley as BG mentioned.

It's not a big deal if I don't convince anyone else of this, but I was just answering a question in the original post here when I started talking about it. I don't even think of anything I'm saying as being particularly scientific or quantitative, it's just a simple matter of looking at a slow motion video of a pro hitting a groundstroke and you can clearly see that energy (or force) is being transferred from their feet to their legs, to their hips, to their shoulders, to their arm, to their wrist, to their racket and to the ball. And since one of the most fundamental laws of physics is that force = mass x acceleration it doesn't take an advanced degree or a bunch of scientific experiments to determine that given two people with the exact same stroke (including rate of racket head acceleration), the person with more mass will impart more energy on the ball. I really don't see how someone who knows a lot about physics could disagree with that.

And John you keep mentioning that you don't think that it's "productive" or "valuable" to keep talking about something so theoretical and, in your opinion, unknowable, but as I've said earlier, I think it's so simple that it's beyond the realm of theoretical, and as a tennis instructor I don't see how you could say it's has no practical implications. What I'm talking about (most of which that usta page also talked about) is pretty much the most fundamental aspect of the game physics-wise. How a tennis player uses his/her body to impart force on the tennis ball. I'm not saying that you have to believe what I'm saying, but it doesn't make sense to say that if what I'm saying were true it wouldn't matter anyways, which is pretty much what some of your posts were saying.

I really don't mean to or want to make any of what I'm saying sound like a personal insult or attack on anyone, but I'm just trying to get my point across.

[BrianGordon]

Appreciate the psychological profile - but I really only had one question for you - your answer had nothing to do with it though I understand it was easier to attack its genesis - if you question the methods of, if not me, the discipline then state your case - clearly you have done a lot of research to form this option - to question the legitimacy of an entire scientific field deserves at least that - no?.

[airforce1]

Uh, if beyond the scope means there is no hard evidence to support it, sure, beyond the scope. It's fun to speculate about how the body works. I do it all the time. That's different though than using scientific and biomechanical terms that aren't tied to actual analysis of the motions under discussion. That's where I think we can get out of our depth. I've been chastened by that experience many times! Actually wrote once that the ball accelerates after the bounce on the court...

That was a test right?

Since acceleration is rate of change, the ball does accelerate after the bounce, right?

LOL, Seriously, I'm just joking around.
We have to lighten up sometimes.
John, it is one of the things I love about your site. You almost always show patience and respect to your posters (who rarely have near the experience in the field as you), as they enjoy pursuing this passion here on your site. I can remember back at the old site that some of the others involved there, didn't do this as well as you always do!

[airforce1]

As I am the only person around here (and one of handful on the planet) that produces quantitative data on tennis strokes I consider your post offensive.

So… we’ve moved on from inferior subjects to questioning credentials and methods. OK, I’m here to learn like everyone else, so please enlighten me as to the proper training and methodology to produce viable measurements – be specific please.

No one will ever mistake you for humble, will they?
I'm not surprised at all that you have taken offense, as you have shown this tendency often in the past when you "think" others don't hold your work in as high esteem as you do. You tend to read a lot into things for someone who is so interested in proof and data. Yes I admit, I don't put a ton of faith in work that "just a handful of folks on the planet" do. That's not a reflection on you personally, but the work as a whole. As more get into it and it matures, it should get more dependable. In my years I've seen a lot of this type of work crumble when better tools became available.

And I did not question your credentials But I find it interesting that you would try to make this about you. But on the other hand now that you bring it up, why wouldn't we question before we put much stock in your work? I would expect a man of science to appreciate that approach.

I remember last time when I had questions about your serving data, I found out that you didn't even have one elite pro server in the group. You were really offended when I pointed that out then too. Since it left the info pretty useless for the discussion it was being used in, maybe I'm the one that should have been offended? Is that specific enough on training and methodology. Let's have elite pro servers in the group when we cite data about what elite pro servers do differently. But that didn't mean you did a bad study and I'm sure it has it uses in some applications at lower levels.

My intent had nothing to do with you, As it was to avoid overlooking the credentials of many of the posters we have on this forum. There is room for that isn't there. Must admit that you didn't even come to mind personally and I didn't realize that you were the "only one around" providing this type of data until now when you shared it with us.

[johnyandell]

Uh, if beyond the scope means there is no hard evidence to support it, sure, beyond the scope. It's fun to speculate about how the body works. I do it all the time. That's different though than using scientific and biomechanical terms that aren't tied to actual analysis of the motions under discussion. That's where I think we can get out of our depth. I've been chastened by that experience many times! Actually wrote once that the ball accelerates after the bounce on the court...

[airforce1]

No, my point is this--I don't think it makes sense or is productive to make quantitative arguments without having quantitative data. You get to the point of he said versus he said very quickly. Like I said, carry on, but it's not something that seems valuable from my point of view. If Brian comes along and eventually lays out some framework to actually evaluate these kinds of claims, great. But even then there is still the issue of why versus how. I'm not sure an explanation of the kinetic chain is the info the average player needs (and higher level players even more so) to improve their forehand...

You make very good points as always. I can clearly see why you would step back given your point of view.
My main point is there is no need to pass judgement that this is beyond the scope of your very educated readers, in the process of pushing back.
My other point is that while BG does outstanding work that can be very useful in attempting to sort things out, this work is still subject to errors in measurement, as well as data interpretation. I'm not saying it isn't worth his valuable effort, just that these evaluations are not the end all some seem to think. Even if most of it is very accurate (if ever done) it is decades behind the ideas and discussions that have led to it.

So while I respect your opinions and choice not to participate in the discussion that you can't appreciate, I can't agree with your assessment that it is beyond the scope of the posters and better to just wait on a study that may never come.

[BrianGordon]

I don't think you mean any disrespect John, but you might want to consider that this clearly is not the case with many of your readers and posters.

I agree that John meant no disrespect, but a reasonable person would have to conclude you did. As I am the only person around here (and one of handful on the planet) that produces quantitative data on tennis strokes I consider your post offensive.

Also you have mentioned your trust in numbers and measurements, but we have to remember that the measurements are only as good as the one doing the measuring and the methods employed.

So… we’ve moved on from inferior subjects to questioning credentials and methods. OK, I’m here to learn like everyone else, so please enlighten me as to the proper training and methodology to produce viable measurements – be specific please.

Many times tech folks who measure are not the same ones who do the innovative thinking either.

There is no differentiation in sport biomechanics.

Often, good ole experience is the basis for new and innovative ideas, and numbers proving the hypothesis come years later.

Tempting but - nah.

Einstein worked out his ideas based on how he saw things working, then he and others were able to build proofs and observations to support them over the ensuing decades. So lets don't write off folks gut ideas too quickly.

Einstein never confused mass with weight, speed with acceleration, associated f=ma with rotational motion, described mass and speed as transferable forms of energy, abstracted the kinetic chain into nothingness, or considered weight transfer a mechanical concept, to name a few.

To the point of at least the latter part of this thread, getting the weight behind the ball or transferring weight into the ball is a coaching concept. The mechanical concept is motion of the center of mass and associated linear momentum. In both cases the impact on racquet speed (shot power) at contact is so negligible I don’t even report it when assessing contributions to racquet head velocity on ground strokes.

This makes sense intuitively on a backhand (primarily neutral/square/closed stance) stroke where the contact of the front foot on the ground and impending leg drive, near the end of the backswing and during the forward swing respectively, serve to stop any forward linear momentum of the body. This is by design to generate angular momentum for the body.

The case put forth by oliensis of effective mass is more compelling but really just represents different system definitions. Differences in speed of the end point across different techniques in the examples cited will be due to a combination of altered range of motion, altered joint rotation contributions, altered muscle moment arms and associated muscle lengths, and changes in the velocity of muscular contraction needed to rotate the joints among others. The primary difference between a straight arm forehand and the double bend for example, is not one of effective mass, but rather one due to alteration of the way upper arm rotations contribute to racquet velocity and what that means for other joint rotations.

Finally, if the velocity of the body center of mass is linked to a large proportion of the racquet head velocity, as on a classical volley due to minimal joint motion, getting “the weight” behind the ball can be important to racquet speed at contact – so I guess it is no coincidence that the timing of the step with the front leg relative to contact is radically different than on a ground stroke.