The paradox of angular vs. linear momentum in the forehand and a possible solution.

[spacediver]

One of the themes of forehand instruction that never really made much sense to me was the idea of driving through the ball towards the target, while at the same time using rotation of the body to power the stroke.

The path that the racquet takes during the follow through is clearly a curved one (imagine a curve that is drawn on the plane parallel to the ground), yet we are often told not to swing across too much during contact, and rather to drive through the hitting zone.

To me, this sounded very strange. The body and arm should be rotating fluidly, and the idea of switching from a straight path to a curved path makes very little biomechanical sense.

But then, I realized that the wrist changes everything.

By gradually laying the wrist back more and more during the "linear" portion of the stroke, your arm can still be "helicoptering" but the racquet face will end up pointing in the direction of the target for an extended period of time (though it will be sliding towards the left ((for right handed forehand)) as it does so).

So if you were to view the stroke from above, and traced the path that the hand takes, it would be curved throughout the entire motion. But if you trace the angle of the racquet face, it spends the critical part of the stroke always facing the target.

The beauty of this is the motion dependent effect upon the wrist joint. If you keep a relaxed wrist, it will naturally lag behind (i.e. wrist joint will naturally extend).

Perhaps this is all common sense to many, but it was a bit of a revelation to me.

-Marwan

[bottle]

It was once a bit of a revelation to me, also, but now I know it's only true of some shots. Using Federer as the example, if you really study his videos, you'll see that he often both opens the wrist and closes it coming into contact. The book Technical Tennis put out by the racquet stringers saw things the way you just did. Their schematic of Federer shows wrist going backward during contact. But this only happens on some of his shots, and anyone can learn both ways of hitting the ball.

[uspta990770809]

Good visualization

Good explanation Marwan. Check out the video someone recommended here in a recent post:

http://www.youtube.com/watch?v=pPLmCqGIotM

Especially, check the overhead view at about 4 min 44 seconds in and the animation with the lines drawn for racket head path at about 5 min 30 sec in. Too bad he didn't draw the lines on the overhead view. I think it would bear out what you are saying pretty well. But Bottle is right too. There is not just one way to hit the ball. Or even just one way to hit the ball well.

I think it is instructive sometimes to remember the ball only knows about the part of the racket that it is touching and that is effectively moving in a RELATIVELY straight line during the 4 milliseconds of contact (I think!).

But, boy, do I wish I had an APAS system. Those things are neat!

don

[spacediver]

It was once a bit of a revelation to me, also, but now I know it's only true of some shots. Using Federer as the example, if you really study his videos, you'll see that he often both opens the wrist and closes it coming into contact. The book Technical Tennis put out by the racquet stringers saw things the way you just did. Their schematic of Federer shows wrist going backward during contact. But this only happens on some of his shots, and anyone can learn both ways of hitting the ball.

Yes I've noticed this before I think. In fact, it was most apparent when I saw him live in Toronto this summer. I wonder if he generated torque in his wrist joint (by activating forearm muscles that control wrist flexion) to do so, or whether he's harnessing some other form of motion dependent effect, perhaps by slowing down the rest of the arm so that the wrist becomes the end of the whip.

[spacediver]

Good explanation Marwan. Check out the video someone recommended here in a recent post:

http://www.youtube.com/watch?v=pPLmCqGIotM

Especially, check the overhead view at about 4 min 44 seconds in and the animation with the lines drawn for racket head path at about 5 min 30 sec in. Too bad he didn't draw the lines on the overhead view. I think it would bear out what you are saying pretty well. But Bottle is right too. There is not just one way to hit the ball. Or even just one way to hit the ball well.

I think it is instructive sometimes to remember the ball only knows about the part of the racket that it is touching and that is effectively moving in a RELATIVELY straight line during the 4 milliseconds of contact (I think!).

Thanks for the video - the 4:44 mark illustrates the concept quite nicely, though in this case, the wrist is already fully laid back well before contact, instead of gradually becoming more and more laid back during the contact phase.

Either way, you and bottle's responses have shown how perhaps the notion of linear racquet path may be something of a myth.

But, boy, do I wish I had an APAS system. Those things are neat!

don

I remember trying to look up the APAS system a few weeks ago. Information on how it works is hard to come by, and their website wasn't working properly. From what I gather, it uses multiple cameras to build up a three dimensional image, but I'm not sure I'd trust it as much as using motion sensors on the body. I can't wait to see Brian Gordon's forehand data in the same module setup that he has for the serve!

[uspta146749877]

bg had a post about apas, i believe

If my memory serves me well bg had a post about apas but I have been wrong before

[bottle]

Whipping Wrist?

spacediver--

In post # 1 here you say, "The body and arm should be rotating fluidly..." Me,
I think the wrist should do that, too, whether opening or closing at the same time. In post # 4 you say of Fed, in Toronto, "I wonder if he generated torque in his wrist joint (by activating forearm muscles that control wrist flexion)... or whether he's harnessing some other form of motion dependent effect, perhaps by slowing down the rest of the arm so that the wrist becomes the end of the whip."

I've always thought this a pretty good question though I think I've been mocked for it. But I'm not interested in a tennis where you can't have ideas and question assumptions.

I'm very influenced right now by the California champion and coach who doesn't think anyone should claim possession of tennis ideas, that we can all have and use them and never give a thought to attribution but take them at will. He would go with your fluidity idea rather than your whipping idea, I'm pretty sure, at least on ground strokes.

But Al Secunda, another California pro, used to talk about "sanding" the ball
on a topspin serve and getting the pressure just right for doing that, too--
doesn't seem like "whip idea" to me.

But I don't know. I like to think about it. Does slowing something to make
something else speed up really apply to wrist? Or better to forearm? Or to whole arm?

Sudden change of direction can definitely accelerate forearm from a totally
relaxed bent elbow on a backhand slice-- I know that from first-hand experience. I wonder if sudden flaps of the wrist weren't what injured Del Potro (along with causing him to win the U.S. Open).

Anyway, Doug King talks about "keeping the stroke in hand" on the ground strokes he teaches. He likens the forearm-and-wrist action (a single action)
to someone twirling a baton-- controlled and not ultra-sonic in other words.
Elsewhere he speaks of "holding" the ball with hand while administering the
body blow of "sling don't swing" and suggests Federer maybe opts for added racket head speed over doing this more than some other players.

As Don says, there's no one way of hitting the ball, but I don't think most people are aware enough of different possibilities.

I may love the idea of speeding up the wrist but I love the idea of slowing it down, too. The latter route immediately has a larger effect on the rest of the stroke, I believe.