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Geoffrey.walsh
06-27-1999, 03:58 AM
Tennis - I am posting below the replies etc as a result of my questions
a few days ago

Geoffrey Walsh
----------------

I have been watching Wimbledon on TV.

When a serve is about to be delivered the player at the other end
invariably makes some preparatory movements.

These consist of a sideways rhythmic motion of the torso, apparently
most of the movement being at the hips.

The rate is perhaps 1 Hz

What advantage is there in doing this. ?

I can think of two possibilities.

1. It keeps the leg muscles ready for action and

2. It provides optical parallax thus enhancing distance perception

Are either of these explanations correct ?
---------
From: bruce elliott
To: Geoffrey.Walsh@ed.ac.uk
Hi Geoff
What you have stated may be true. I would add that it may be better to
jump into a split step(pre-tense muscles and store elastic energy) from
a system that is already moving.
Regards
Bruce Elliott
Professor Bruce C Elliott
Head, Department of Human Movement
The University of Western Australia
Parkway Entrance No.3
Nedlands, Western Australia, 6907

Telephone: +61 8 9380 2360
Facsimile: +61 8 9380 1039
E-Mail: Bruce.Elliott@uwa.edu.au
www: http://www.general.uwa.edu.au/~hmweb/index.htm
-----------------------------------------------------------From: Jack
Sujovolsky

Dear Mr Walsh:
What I think the most important preparatory motion is when the opponent
is ready to strike the serve...It is here that the receiver does the
short hop to "unweight" himself, and load the muscle with energy. The
sideways motion I believe is just a pendulum action, that is believed to
help in reacting to the proper side that the ball is coming to...Serves
are coming at such a high speed, that turning at the hips as quickly as
possible is the key..Turning the hips is the fastest way of initiating
any kind of backswing...I dont see any physical benefit from the swaying
at the hips, but to the player, it must be a
comforting ritual...like testing the motion right to left..

Jack Sujovolsky, MS, USPTA
-------------
From: Ian Fisher

Hi Geoffrey,

The short answer is I've no idea but I did think of a third
possibility - the side to side motion makes it makes it harder for the
serving player to focus on the 'returner' and consequently harder to see
the racket swing. I'm not an expert on vision but this is the usual
explanation for why ice hockey players make similar side to side motions
before shooting the puck; that means it's harder for the goalie to focus
on the player and the puck.

Interseting question,
Ian.
Ian Fisher 0171 589 5111 ext 57104
-----------
From: "Devita, Paul"
Geoffrey,

The main preparatory motion I see in the service receiver is the well
timed knee flexion that occurs just prior to racquet-ball contact in the
serve. Edberg had the best example of this motion. He would start well
behind the baseline and move forward as the opponent was doing the
service motions. Just prior to the moment of the serve, Edberg would
make his final forward movement, landing on both limbs about
simultaneously, and flexing
both knees (with some hip flexion and ankle dorsiflexion also). This
motion prepared the quadriceps (and other muscles) for quick and
powerful contractions by preactivating this muscle, stretching the
elastic tissue, and activating muscle spindles. Essentially, he
incorporated the stretch-shortening cycle.

By, "sideways," motion, you must be referring to turning the trunk
around a near vertical axis, the longitudinal trunk axis. This motion
will certainly prepare the player to more quickly turn the trunk for
either a forehand or backhand service return. This twisting motion would
be performed by the various muscles surrounding the trunk, particularly
the internal, external obliques. I do not think this trunk motion
contributes much to
lower extremity muscle contractions but it might require some low level
activations to increase support for the moving trunk.

That's my uninformed opinion,
Paul DeVita

--------
From: Dan Major
As a (former) tennis player, I can think of two reasons a player in the
receiving court sways -
1) to keep balance transfered forward, to the balls of the feet so that
he/she is able to react quickly, and 2) a nervous affectation. You're
keeping perception and awareness maximized, and this has an "outlet", if
you will, in the player swaying, or dancing from foot-to-foot.

Just the point of view from a player.
--------------
From: Simon Roe

I think it is more a balance readiness issue - weight moves forward,
preparing for the return

Simon Roe

From: "Al Vangura Jr."
Geoffrey,
What about pretension of the leg muscles for quick/powerful
contractions?

Al Vangura Jr.
Univ of Pittsburgh
Musculoskeltal Research Center

---------------------
From: AngelEB@aol.com

Geoffrey...I am a graduate student and was intrigued by your statement
regarding "optical parallax". I have never heard that term...am able to
"intuit" what it might mean...but was hoping you could explain it to me.
Thank you in advance for the education. Angel.
---------
From: "Geoffrey.Walsh"

To: AngelEB@aol.com

It is possible to prerceive distance with one eye by moving the head.
The chicken does this I think, cocking to head one way and then another
before pecking a gain of something. By moving spatial data can become
apparent (or more apparent). You get a different view which the brain
can build up in 3D. Ordinery binocular vision will not be much good over
the distance of a tennis court as the eyes are too close together.
Parallax will help..

GW
-------
From: yanagawa@mail.utexas.edu (Takashi Yanagawa)
To: Geoffrey.Walsh@ed.ac.uk

Hello.
I thought this topic was interesting.

First of all, I'd like to know what the top tennis player say about this
as
well as their coaches.

This sounds unprofessional and non-technical. But I just simply think
that
a reciever just want to show to a server that he/she is ready to move
either right or left side. It's just a message to the server from the
reciever.

I don't know anything about optical parallax. Anyway, I don't think he
has a time to percieve the distance in such a short time. Even he
could, I don't think he has a time to change his motor program soon
enough to return the ball.

Let me know what others say.

Thank you.

Takashi Yanagaw
------------
From: "MILES, ERICA H. (JSC-SP)"
To: "'geoffrey.walsh@ED.AC.UK'"

I'm in no way an expert at tennis (just a fan and a player/tinkerer),
but your explanation #1 is pretty correct from what I've been told.
Also, another tennis tip I was told is: as the opponent's racket makes
contact with the ball during his/her serve, the receiver should
split-step -- in my opinion, this readies the legs, improves balance,
and may also add to mental preparation. This seems to help in keeping
me ready to return serves from both (forehand and backhand) sides, plus
decrease reaction time for the service return.

Your second theory is interesting -- I've never really thought about
that, but it seems like a possibility...

regards,
erica :)




--
Email— Geoffrey.Walsh@ed.ac.uk
http://www.ed.ac.uk/~gwalsh
Phone (0)131.664.3046

64, Liberton Drive,
Edinburgh
EH16 6NW
UK

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