Friday, May 20, 2011

A Roadmap to a Hall-of-Fame Forehand - Part 1: What is the Racket Really Doing in the Impact Zone?

Last time, we left you with this image showing you the positions of the racket face and the shape of the racket path during the forward swing to impact that are used by arguably the best two forehands in tennis today:

Now, let’s begin drilling down into what you can learn about these two “strokes of genius” (as well as some the other great forehands of recent years – like the cannon demonstrated by the Chilean great, Fernando Gonzalez) help you create your own “SlamMaker” forehand that enables you to maximize both ball speed –“power”—and topspin—“control”.

A really good place to start drilling down into the forehand mechanics used by today’s top players by taking a closer look at what the racket face is doing in the “Impact Zone” of the stroke – i.e. what the racket does in the 3 feet before impact, at impact, and 3 feet after impact.

This is not to say that there aren’t other factors—grip, shape and size of the backswing, the size and shape of the follow-through, etc.—that strongly influence the speed, spin, trajectory and placement of the resulting shot. We just need to start somewhere, and in our opinion, that place is to really look carefully - mindful of any lurking "inattentional blindness" issues that are always lurking about (remember the moon-walking bear in our last post?)- at the most fundamental interaction of the racket, strings and ball which happens in the moments before and after impact.

I Can See Clearly Now...

First, let’s discuss some important background information that is necessary to understand the context of our findings regarding the “behavior” of the racket before, during and after impact. In general, I would say we are heading into somewhat uncharted waters because first, and foremost, it wasn’t really practical to even undertake this type of research and analysis because the necessary tool required to even gather the needed information to resolve clearly what rackets and balls are doing in the 3 feet before and after impact was simply too expensive to access.

Before 2008, the high-speed video technology need to see clearly what’s going on in the 35 to 40 milliseconds it takes a top player to move the racket the 6 to 8 feet of their Impact Zone was limited to the military and industrial-grade high speed video systems- capable of incredible frames rates in the 100,000-plus frames per second (“fps”) range to study, for example the initial trajectory and spin rates of bullets fired from guns. And, the pricing for this technology generated started in the 10s of thousands of dollars.

So, the fantastic costs involved in making even the most basic high-speed video study of tennis motion naturally proved a significant roadblock to overcome.

A few sport science researchers bit the bullet and bought or borrowed high-speed video equipment to dissect the intricate details of athletic movement and performance, and tennis has had its share of high-speed video-based research in the past 40 years. Western European and East Bloc countries started performing high-speed video studies of their elite tennis players starting in the early 1970s, and folks like Vic Braden and Gideon Ariel started filming tennis motion using high-speed cameras at about the same time in the US.

Truth or Beauty – How informative are your favorite instructional videos?

So, the great majority of the high-speed video footage, until John Yandell started the Advanced Tennis Research project in the late 1990s, was taken of the sport as it was performed in the 1970s. Yandell should be given all due credit for taking the initiative to pay the steep price and start taking high-speed footage of the current top players.

The limitation of the Advanced Tennis and now, TennisPlayer footage, however visually stunning, is that a lot of that footage is not usable from an analytical, quantitative perspective. Mainly, through no fault of their own—as he and his team did not have much control over where they could place their cameras in various stadiums in the US and Canada—the camera angles and perspectives of their footage deliver mainly qualitative information.

Therefore, the great majority of TennisPlayer articles cannot go too far beyond descriptions of what they see on the videos, and while they do see much more detail using high-speed cameras, the authors on that site do not have the necessary, integrated background in the knowledge areas – anatomy, physiology, physics, neurobiology, biomechanics, etc. – to clearly explain why certain moves are made, what the results of the moves are for different players at different levels, etc. Mainly, the articles tend to cherry-pick the footage that justifies long-standing instructional ideas, concepts and methods.

More recently, the introduction of Exilim High-Speed camera line by Casio, starting with the Exilim EX-F1 in 2008, puts what is essentially a “sports motion microscope” into anyone’s hands. But, as with anything, it’s not the “data” itself that is most valuable, it’s making sense and meaning from those data that truly matters.

With that said, here is what you need to begin to understand about what’s going on in the impact zone of a top player’s forehand by looking directly at how they themselves move their rackets though the Impact Zone.

Three Questions Every Player Should Ask Themselves...

Let’s start with three very basic questions:

What is the racket doing in the Impact Zone?

What is the position of the racket face before/during/after impact?

What variation in racket motion exists as it moves in the Impact Zone?

Oh yes, there’s one more important detail I would like to mention before we start attempting to answer these three questions. Given the reality when players compete in live matches, we need to understand that the unpredictable nature of match play forces players to adapt their stroke mechanics to the highly variable situations that emerge during live play. Therefore, to reduce the higher levels of variation in the stroke mechanics – the body and racket motion – that is inherent to competitive play, we will try to limit our analysis to the strokes players used in their (cooperative) warmup before training sessions or in their in their pre-match warm-ups during tournaments.

In this situation, they encounter far less variation as they execute their strokes mostly down the middle of the court (you know how you would feel if your partner were jerking you around the court instead of keeping the ball in the middle during the warmup!), so this enables us to witness what effectively is their “base mechanics”, or most fundamental stroke mechanics.

Then, from these “base” mechanics, the player will then adapt these mechanics (adjusting speed, spin, trajectory, direction, etc.) to the highly variable challenges they face during live competition.

How Much Can Really Happen in 30 Milliseconds Anyway?

So, let’s take a closer look at what Federer and Nadal achieve in the Impact Zone of their forehands:

With the help of our video analysis software of choice, V1 Pro, we marked the position of the racket face as it moves through the Impact Zone using the following convention:

Yellow lines mark the racket face position before impact,

A green line marks the position at impact, and

Red lines mark the positions after impact.

As the video was captured at a speed of 210 fps, the time that elapsed between each line is 1/210 or 0.0048 seconds or 4.8 milliseconds.

We traced the position of the racket face starting 5 or 6 frames or 4.8 X 5 frames/ 4.8 X 6 frames = 24 milliseconds to 28.8 milliseconds before and after impact. We also estimated the angle of the racket face at different stages of their stroke: i.e. 1 frame before impact, at impact, and sometimes, 1 frame after impact and at the stage in their follow-through when their racket arm reaches shoulder level.

Now, let’s start really drilling down on the first two questions we posed: what is the racket face doing in the impact zone and what is the position of the racket face before, during and after impact?

Here’s a close-up of the trace of the racket motion of each future HOF’s forehand in the impact zone:

The first thing you should notice is that both players tilt the racket forward throughout the impact zone – i.e. the racket face is closed at every millisecond in the impact zone. Not open — tilted upward toward the sky— nor square or vertical — where the racket face is oriented perpendicular to the court — but closed at all points in the impact zone, even at impact.

This observation alone should bring to a conclusion a long-standing debate about how players today produce topspin on a forehand. This image alone shows conclusively that players do indeed tilt the racket forward when they execute a topspin forehand, and the racket face remains tilted forward at impact, often at an angle that is much farther forward that had been previously thought possible.

At impact for the forehands shown here, Federer’s racket face is tilted forward 11 degrees at impact and Nadal’s racket face is tilted forward 15 degrees (relative to a perfectly vertical racket face.

And the racket path used by each player for the same forehand as shown above is interestingly the same: the racket for both Federer and Nadal are moving 18 degrees upward…

Both elements – the forward tilting of the racket face, and an upward – or “low to high” – swing path are used by these HOFs to create contact to produce a shot that commonly leaves the racket at ball speed over 80 MPH and topspin rates upwards of 3,000 RPM.

Now, while these observations very much sound like "old hat", when we started to look deeper into the usefulness and validity of the age-old topspin mantra of "swing low-to-high with a vertical racket face", we found an interesting disconnection between the "theory and reality" of topspin production.

Does "Theory" Really Match the "Reality" of Topspin Production?

In an ideal world, whenever people make a sound, thorough and objective analysis of any subject, the "theory" and "reality" should match one-to-one.

Given what we observed about how Federer and Nadal really move their rackets through the Impact Zone on their respective forehands, we conclude that there seems to be a gap between "theory" and "reality" when it comes to understanding how massive topspin is generated by today's top players.

When we tried to look for more information on the subject of topspin production on tennis groundstrokes, what we found was that this type of really fundamental information about racket motion in the Impact Zone is not widely known or studied, much less published. We eventually found a few coaches and researchers offering some tidbits here and there from their work, much of which is very hard to access, even with the Internet.

We found that there are two "schools of thought" about the "theory" behind topspin production on groundstrokes (based on published works in English).

The first "school of thought" behind topspin production - "get the racket below the ball then swing up on the ball steeply from low-to-high with a vertical racket face" - is best described in a 2001 article by Vic Braden in the late Eugene Scott’s “insider magazine”, Tennis Week.

In the article titled: “Top Ten Tennis Myths – Myth 3: Rolling the Racket Over the Ball for Topspin” (published February 13, 2001), Braden wrote this:

A highly debated issue, at the moment, is the position of the racquet face when it impacts the ball. On a typical groundstroke, a vertically positioned racquet at impact, when the racquet was traveling upwards at approximately 17 degrees, produced no topspin. Therefore the racquet must be traveling at rather severe upward angles to generate the desired topspin. The exaggerated example is when players want to generate excess topspin to hit short angled passing shots, they often swing close to 90 degrees upwards and finish the follow-through over their hitting shoulder. We have digitized some shots where the racquet face is pointing downwards five (5) degrees. We have seen a racquet face pointing downwards nearly twenty (20) degrees on a half-volley when the incident angle is severe and the player is trying to keep the ball close to the net tape. However, we have film on several top players and their racquet face is normally vertical when impacting the ball on groundstrokes, even the big time topspinners.” (page 34)

The second "school of thought" behind topspin production on groundstrokes -where topspin production is the result of striking the ball with a racket face that's tilted forward - is best summarized on pages 131 to 135 in the 2005 book “Technical Tennis—Racket, Strings, Balls, Courts, Spin and Bounce” by Rod Cross and Crawford Lindsey.

There, in “Match Point Box 4.3” on pages 134, they mention that an analysis of a midcourt topspin forehand struck by Federer showed that Fed’s racket face was tilted 8 degrees forward at contact and the racket was moving upward at a 30 degree angle. Based on these observations, Cross and Lindsey rightly concluded that after seeing the racket motion of Federer’s racket using high-speed video (at “only” 125 fps) that concluded that Braden’s view needs at the very least, to be re-visited:

For example, many coaches still believe that the racquet face must be vertical to hit a topspin forehand or backhand. However, Roger Federer and many other players tilt the racquet forwards, especially on balls hit above the waist. Sometimes the ball is not struck in the middle of the strings but lower down near the frame. As a result, the racquet head rotates during the shot so that the head is tilted forward by the time the ball leaves the strings.” (page 135)

Later, on pages 137 to 139, Cross and Lindsey present a more detailed explanation of topspin generation, and even provide a schematic (Figure 4.10 on page 138) showing what happens as a result of varying the racket path angle and racket tilt on topspin generation.

But, like many “laboratory - ” or “thought experiments”, when we started looking at these questions ourselves, we find quite different results when it comes to topspin generation during live play (we’ll discuss this much more complex topic in a later post).

Time to Revisit the How-To Behind Generating Topspin?

Clearly, even our somewhat simplistic look at racket position and motion in the impact zone shows that, from a coaching perspective, Braden’s view of the vertical racket face plus low-to-high, upward swing path being the primary mechanism behind topspin production on a forehand isn’t correct.

The spin rate of the Federer forehand shown was 2,300 RPM and the spin rate of the Nadal forehand was nearly 2,600 RPM, and such enormous spin rates are hard to reconcile with Braden’s 2001 view of topspin production for the forehand. Both Federer and Nadal have their rackets tilted forwards more than double the amount—in this case, 11 and 15 degrees forwards compared with the 5 degrees forward tilt Braden and his colleagues found among players up until early 2001), and the overall path of racket motion was exactly the same as — 17 degrees upwards — as the racket path that Braden and his colleagues showed produced 0 RPM - no topspin whatsoever - albeit under laboratory conditions, if I remember correctly.

Clearly, this difference between “theory” (at least whatever was Braden’s view of how topspin is generated) and “reality” means that we need to be taking a much closer look at what factors are necessary to generate the ultra-heavy spins we are seeing today…

And, I can tell you that it’s not solely the result of the “modern equipment” and the higher swing speeds used by today’s players.

When we look most of the bigger forehands used on tour today, we see exactly the forward tilt of the racket face at impact and throughout the Impact Zone (with certain exceptions—which we’ll also discuss somewhere in the not-too-distant future, I hope) and a relatively shallow (generally less than 20-22 degrees upward - which is nearly 30% shallower than the path shown in Cross and Lindsey's Federer analysis) rather than steep upward racket path.

First up, let's look at the racket motion in the Impact Zone and the angle of the racket face at impact (itself) for Fernando Gonzalez and Nicolas Almagro…

Next up, here are Kei Nishikori and Fernando Verdasco…
(Hey, maybe if you want to develop a monster forehand, you might also consider changing your name to Fernando?)

Now, here are Marat Safin and Andy Roddick...

And to close these proceedings, here are Novak Djokovic and Tomas Berdych...

Maybe, what we need to take home from these observations is that these—now visible, due to greater access to high-speed video—differences in racket motion in the Impact Zone used by this generation of top players are the core “innovation” or “evolution” of forehand mechanics—driven by player ingenuity, if not “player genius”—between 2001 and today. Certainly, the ability to generate much higher amounts of topspin is absolutely necessary maintain both control and precision given the higher racket speeds and ball speeds sought by today's ATP competitors, in general.

Cross and Lindsey at least recognized in 2005 that certain players were clearly creating racket motion using their forehand mechanics that were significantly different from the “classic models” and "theories" like those championed by folks like Braden, Lansdorp and literally just about everybody else.

Now it’s 2011, and our initial analysis of the racket motion through the impact zone, combined with our measurements of spin rates of the top forehands on tour shows that, at this point in history, the huge gulf between existing “theory” and “reality” of topspin generation means that we still have quite a ways to go before we actually have a solid understanding of how racket motion through the impact zone and racket tilt actually influence topspin production.

Now, when you then realize that the vast majority of tennis coaches, instructors and internet gurus still push the classical topspin mantra of "get the racket well below the ball, keep the racket vertical and swing low-to-high, and brush up on the ball", can you really expect them to help you develop a topspin forehand that performs like your favorite pro player?

So, how do you apply what we’ve discussed here to your forehand?

First, you have to get your head around this “novel” method of generating topspin…

Because if your brain doesn’t understand what it is you’re trying to achieve, you’re stuck until you get to that point where you “can wrap your head around” the ideas and concepts needed to achieve the forehand mechanics of today’s top players.

The first step is to forget the claasical, “keep the racket vertical and swing low-to-high steeply” advice that many of you have been hard-wired into your tennis brain and begin thinking and doing the opposite:

Which is…

Shut the racket face down throughout the entire stroke and shallow out your overall racket path, especially in the impact zone.

Further details of how to achieve this type of racket motion at the racket speeds needed to produce the identical results as players like Federer and Nadal are going to fill a lot of future blog posts, folks.

And one last thing...

Sorry, But The (True High-Performance) Menu Is Not Big...

And contrary to another false paradigm of tennis instruction: if you start to look carefully at what those players on TV are really doing, it becomes clearer that there is really only a very specific set of movements that can be used, arguably only one way to achieve the same forehand mechanics, and therefore the same forehand spin and speed performance of Federer and Nadal and other ATP stars.

The naked eye cannot see—no matter what your coach, Internet guru or park instructor says or writes—cannot distinguish the “micromotion” that defines today’s HOF forehand. As no two humans are built the same, any two forehands will “look” different to the naked eye. But from a more objective perspective, the stark reality is that there is only a very limited and defined set of movements that must be made in a certain sequence to produce a SlamMaker forehand.


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At 1:52 PM, Blogger Antonis said...

You are living out an important aspect. Which part of the ball are you hitting? Check this out, it is interesting:

On a more practical tone, it could be interesting thing to study the motion of the racquet handle axis during contact, isolating it from other motions, the way you did with the Y axis.

Thanks, good job.

At 10:59 AM, Blogger Ahmed said...

Very informative post.
Thanks for sharing.
I'm wondering why no great american tennis players these days if america got brains like you !!!


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