Tour Strokes:
Kei Nishikori Serve

Analyzed by John Yandell

There was some press coverage earlier this year about the changes Kei Nishikori made to his serve motion in response to his chronic wrist and shoulder problems. As one writer put it: "The change to the motion comes in the take back. These days Nishikori's path to the trophy position is more abbreviated. In year's past he would draw the racquet low before looping it up to prepare for contact." (For more on this Click Here.)

I had to laugh when I read that. Over the years I have filmed Kei many times including his serve. My opinion is his shoulder and wrist problems have nothing to do with his take back.

If there is one thing we can say about pro service motions it's that there is a wide disparity in the shape of the backswings, ranging from classic semi-circular wind ups to highly abbreviated and everything in between. None of them have associated with injury.

But regardless of backswing shape, all the great servers do share one common element. This element is missing from Kei's serve. It's the rotation of the arm and racket extending into the followthrough after contact.

And guess what? Another top player who had the same restriction in her motion and also chronic shoulder problems was Maria Sharapova, something I wrote about previously on Tennisplayer. Click Here.

Acceleration

Research shows that the vast majority of racket speed occurs between the racket drop and contact. And this interval is a small fraction of the overall time of the service motion.

For example on a 120mph serve, at the drop the racket has reached a speed of around 30mph. In the next 1/10th of a second this triples from 30mph to 90mph as the arm and racket move up to the contact.

Building that initial 30mph at the drop takes about a second and a half, or three quarters of the overall time of the motion. Then the other 60mph--two thirds of the total speed is generated in a blinding flash.

The racket head has moved from basically perpendicular to the court at the drop to parallel to the court at contact. This is roughly 90 degrees of arm and racket rotation.

That motion is driven mostly by the rotation of the upper arm in the shoulder joint, combined with the straightening of the elbow.

After contact the story is equally fascinating. The contact knocks 20mph off the racket speed virtually instantaneously. This takes it down from 90mph down to about 70mph.

And this deceleration then continues at an extremely rapid pace. Within about 1/10 of second after contact, the racket speed is back down to about 30mph.

The hand, arm and racket have continued to rotate during this deceleration phase. They turn about 90 degrees after contact so the bottom edge of the racket is perpendicular to the court.

Although the terminology isn't correct, this is commonly referred to as "pronation." The accurate term is internal shoulder rotation. It's the seamless continuation of the same rotation that drove the racket upward to the contact in the first place.

This rotation is followed by the relaxation of the wrist. It falls so the racket face comes down from the rotated position and is pointed more directly downward at the court.

So there is an interesting symmetry here. It took the racket about 1/10 of a second to go from 30mph to 90mph from the drop to the contact. Now in about the same interval, 1/10 of a second, the racket has dropped back down from 90mph to 30 mph.

Think about that! In 2/10s of one second, the racket goes from 30mph to 90mph and then back from 90mph to 30mph. That's a total speed change of 120mph in a total 2/10s of a second! For more detail on all of this in the 3 Dimensional study Brian Gordon and I did of Pete Sampras's serve, Click Here.

A key point is that this wrist release happens well after the rotation is complete. Usually it happens when the hand has already fallen into the plane of the torso.

It's also relatively slight—a few degrees of forward bend at most. If the arm is relaxed it's probably caused just by gravity as the hand continues to move downward and across the body.

The timing and amount of this release varies from player to player. Sometimes you don't See it at all.

As For Kei

So how does all this apply to Kei? His motion is very different in two fundamental respects.

First he never completes the rotation of the hand, arm, and racket. It stops dead at the contact when the speed of the upper arm is maxed.

Second, at that point he begins an extreme forward flex of the wrist. It starts when the hand is still above his head and continues until the wrist is flexed forward at about a 90 degree angle to his arm.

To me it's painful to watch. What is that violent end to the rotation doing to his shoulder? And what about that bizarre extreme forward flex doing to his wrist?

I have not filmed a top player whose motion looked the same. Of course there is no way to absolutely prove medically that these two movements, and lack of movement, are the source of all his injuries, but in my opinion they are.

A few years ago I was filming at a Masters event, including filming Kei and his serve.

I went up and introduced myself to his main coach, who will remain nameless, and asked him if he would be willing to look at some high speed footage of Kei's serve. Let's just say he wasn't overly friendly, but said he might but later.

He gave me his cell phone number. I called him the next day, asked him the same question, and got the same answer. The next day I tried again but he told me Kei had injured his wrist (again) and they had both left town.

I call it the tour coaching bubble. Most tour coaches are former lower level pro players. They aren't technical and are often anti-technical. This coach eventually left Kei's team and I never ran into him again.

There are a few other factors you could criticize in Kei's serve, like his starting stance, use of the legs and lack of body rotation. But those factors usually don't do joint damage—at least to the arm.

If the world changes and I get a chance to watch Kei play again in person, maybe I'll make one more run at whoever is coaching him then!