Tuesday, June 28, 2011

A Roadmap to a Hall-of-Fame Forehand - Part 2: Does the Impact Location on the Stringbed Matter?

When we first started capturing high-speed video of the world’s top tennis players, one thing that we noticed right away is

1) how often the top players make contact with the ball in places other than the center of the racket face


2) how often and how much the racket twists and in the player’s hands rather than staying “stable”- i.e. no twisting – in the milliseconds after impact

particularly on groundstrokes struck with heavy topspin or underspin.

What we were seeing runs entirely against one of the most fundamental instructional mantras of tennis –the one that goes “hit every shot in the center of the racket”.

What was even more intriguing/surprising was that for some players, especially the ones who have been ranked #1 in the world or have multiple Grand Slam singles trophies to their names, very often make contact closer to one edge – especially the bottom edge – of their racket, especially on their topspin forehands.

What we have seen is that the top players make contact with the ball in one of three (3) fundamental locations on the stringbed on their groundstrokes.

The first impact location is in the upper part of the stringbed that’s closer to the top (or leading) edge of the racket:

The second impact location is in the “geometric” center of the stringbed:

And, the third impact location is in the lower part of the string bed near the bottom (or trailing edge) of the racket:

What you should also notice is what happens to the racket just milliseconds after the ball leaves the stringbed after making contact in each one of the three fundamental impact locations.

When impact occurs near the leading edge of the racket, the racket rotates to an open position (tilts backwards) with the strings pointed toward the sky.

When impact occurs in the center of the stringbed, the racket (face) remains very stable and remains in (more or less) the same orientation as it was before impact.

When impact occurs near the trailing edge of the racket, the racket rotates to a closed position (tilts forwards) with the hitting surface often ending up pointing directly at the ground.

When players make contact with the ball near the trailing edge of their racket on a topspin groundstroke – most commonly on a topspin forehand – the forces generated by the interaction of the ball, racket and strings at impact cause the racket to rotate suddenly in the player’s hand and results in the sudden forward tilt of the racket face.

Even the hand and forearm strength of a tennis champion cannot resist the forces created during the collision of the tennis ball with a racket that’s moving at speeds over 80 MPH that’s encountered during this type of off-center contact.

Now, what could possibly be the reason – the benefit – for making consistent, off-center contact with the ball?

After all, isn’t the ability to strike every shot in the center of the stringbed the very hallmark of a tennis champion?

The most common reason that has been tossed around by various tennis coaches over time is the anecdotal claim or belief that making off-center contact on forehands or backhands can increase the amount of spin generated – either topspin or underspin – on a given stroke.

We are not aware of any (published) direct evidence that supports this idea that off-center ball contact somehow influences – and more specifically, increases spin production in groundstrokes, so we decided to conduct a preliminary study to determine if there’s any relationship between impact location and topspin production.

In this preliminary study, we looked at high-speed video clips of the topspin forehands of the three (3) active players who have won two or more Grand Slam singles titles: Roger Federer, Rafael Nadal, and Novak Djokovic during tournament play and practice on hard courts.

Specifically, we measured the amount of topspin (in RPMs) generated and recorded the type of racket motion through the impact zone – whether or not the racket tilted forwards (to the ground) or backwards (to the sky), or remained entirely stable after impact for a minimum of 60 forehands (struck in a wide variety of situations/court positions) per player.

The table below summarizes what we found:

So, based on this very preliminary analysis of topspin production and racket motion in the impact zone, we conclude that:

The highest topspin rates (nearly 40% higher compared to “center contact”) are produced when impact occurs near the bottom edge of the racket;


The lowest topspin rates are produced when impact occurs near the top edge of the racket.

So, when you see this sequence of images when Roger strikes his forehand, you now know that he is producing much more topspin with his "twisting" racket compared to making contact with a “stable” racket in the impact zone:

We’ll begin exploring the reason(s) why these different topspin rates are related to the impact location on the stringbed, and how these great champions are able to “manipulate” contact on the court during live play…

As well as compare topspin production versus impact location in other, non-current or previous World #1s or non-multiple Grand Slam-winning tennis players in future posts.

So stay tuned.


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At 4:17 AM, Blogger LC said...

Great blog.

At 3:17 AM, Blogger Francis Kwok said...

Hi, thank you for your great blog. How do you think some other video showing pro players hitting the ball close to the tip of racquet? Any speical implications for this position on power/control/spin?


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