Forehand stances and tactical considerations

[uspta146749877]

Please click

http://dps.usta.com/usta_master/usta/doc/content/doc_437_100.pdf

A quote below-any comments?
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Open Stance Forehand
Type(s) of momentum
• The open stance forehand primarily uses angular momentum to generate racquet head speed.
Balance and weight transfer
• To effectively generate angular momentum it is important to have a wide base of support. The ground reaction
forces produced by the feet help create rotational torques that contribute to the angular momentum of the
body.
• The body’s center of mass should remain centered over the base of support as it rotates about the vertical axis.
Tactical considerations
• The open stance forehand is effective in dealing with power and/or generating power.
• This type of forehand shot can be employed when there is little time for the player to prepare (e.g., return of
serve or forced wide in the court), and allows for a quick recovery.

Semi-Open Stance Forehand
Type(s) of momentum
• The semi-open stance forehand uses a combination of linear (as the body’s center of mass moves forward) and
angular momentum (as the body rotates about its vertical axis).
• Linear momentum, directed upwards, also help in the generation of topspin and power.
Balance and weight transfer
• This shot uses a narrower base of support and the body’s center of mass also shifts forward slightly during the
execution of the shot.
Tactical considerations
• The semi-open stance offers great versatility and is effective in dealing with power and/or generating power.
• This type of shot can therefore be used in offensive, defensive or neutral situations.

Square Stance Forehand
Type(s) of momentum
• The square stance forehand primarily utilizes linear momentum as the player’s weight shifts from the rear foot
to the front foot during the execution of the shot.
• A small amount of angular momentum, generated by the arm rotating about the shoulder (and other body
segments rotating about joints), does contribute to the racquet head speed and the force behind the shot.
Balance and weight transfer
• The square stance forehand uses a narrower base of support with the weight being transferred from back to
the front foot. The feet are typically parallel with each other.
• Dynamic balance, especially balance on one leg, is essential in the execution of this shot.
• Although Federer exhibits more body lean in the last sequence, he clearly keeps his head still and is tremendously
balanced in each of the shots.
Tactical considerations
• The square stance forehand is typically considered an offensive shot and is frequently used when moving
forward and/or attacking.
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[airforce1]

I'm still not sold on the term angular Momentum, but this is some very good info to relate to your various stroke situations.

[tennis_chiro]

Primarily linear momentum, my a#*!

With all due respect to Paul Roetert, the body simply does not generate any significant force any other way than levers and pulleys (smiles and frowns may be important but they do not involve significant forces!); that means angular momentum and torque. When you use a square stance, you use the same principles as with an open or semi-open stance. The laws of physics do not change. The difference is where the body places the fulcrum about which it applies its force. In a square stance, imagine the force rotating about a pole through the front shoulder,ideally located directly over the front foot. The movement of the weight to the front foot, which happens before the actual forward swing (if only slightly) enables the player to establish a stronger more stable fulcrum about which to activate the lever arm (the body, arm and racket). All the angles and mathematics make it much more effective to hit the ball off the front shoulder rather than behind (sines, cosines, all that good stuff). It's been a while since I've studied these things and I need some help here from some of the biomechanists, but the idea that you hit the ball with linear momentum is simply wrong. There may be some component, but it is very small relative to the true force the body generates to do anything. Look carefully at those pictures of Roger's square forehand (you really need a baseline view) and see how much the left shoulder is moving forward once the weight is transfered and the racquet starts its move up toward the ball and forward into the court.

Looking forward to getting ripped on this one. please help out, you biomechanists!
don

[uspta146749877]

A different thread to read as well

more discussion on the subject of tactical considerations
is provided in a much less explosive thread

http://www.tennisplayer.net/bulletin/showthread.php?t=1207

julian usptapro 27873
beford,massachusetts

[oliensis]

With all due respect to pullies and levers, there are swings that are more linear and those that are less linear (with tighter arcs).

Remember, an object traveling at a constant rate of speed along an arc is considered to be accelerating. The tighter the curve, the "harder" it is to keep a constant velocity (compare running a tightly curved track to a straightaway). So, the tighter the curve, of the racket head's arc, the more acceleration there is in it when moving at a given velocity.

Torque, or angular momentum, is related to angular veloctiy (the rate of change of the angular position of a rotating body; usually expressed in radians per second or radians per minute).

Longer, more linear swings (as racket moves toward contact point) have lower angular velocity, even if same linear velocity. While velocity may be the same in both cases, that's not quite the same as ACCELERATION (rate of change of velocity). And acceleration is what generates the rate of change in the vector of the ball's flight.

So, a more linear swing, even with the same racket-head velocity, will not generate the same momentum change in the ball that a more curvilinear swing will generate. Why? Because the angular component of the path of the racket head in each swing will differ. Why? Because the acceleration of the racket head will be different in each swing. Why? Because, the angular velocity (rate of change of angular poition of rotating body (radians per second) will be different.


There may be only pullies and levers, the kinetic chain is more complex than just summing linear velocitiies that these pullies and levers can generate. Otherwise, EVERYONE would be able to throw a 100mph fastball.

[tennis_chiro]

Now maybe we can start a discussion

Oliensis,
you have to look at the situation from the point of view of the ball, as well as the player creating the force. The ball only knows about the vector of momentum of the object touching it at the moment of contact. 4 (or maybe 5) thousands of a second later, that object no longer has anything to do with the ball. If the racket isn't accelerating at the moment of contact, it won't even apply any force to the ball beyond the 2nd or 3rd thousanth of a second. To get the solid feeling of "hitting through the ball" you have to have the vector of momentum of the racket head going in the direction you want the ball to go. The ball always goes PRIMARILY (not exclusively) in the direction of a vector perpendicular to the face of the racket. The outgoing direction is also influenced by spin and angle of incidence/angle of reflection considerations. It is also influenced right or left by the right or left direction of the swing (i.e. the classic hacker's backhand across the ball outside in can send the ball forward, but not with much speed). When the vector of momentum of the racket head is exactly the same as the vector perpendicular to the face of the racket (I like to use OncourtOffcourt's Foam Arrow in the throat for the student to understand where he is pointing the ball), you get the most power. Of course, we want spin too, so the ideal duplication would only be in the x and y axes as the racket head should be rising going from below the ball to above the ball as it brushes the ball and creates spin. Remember that that 4 milliseconds (1/250 sec.) converts to more than 4 inches at 60 mph (88 feet/sec.). (1/250 x 88 =.352 feet = 4.22 inches) that the ball is actually touching the strings. Also, realize that the weight transfer takes much more time than this.

The player is trying to get the racket to go through the hitting zone towards the target as much as possible, but because we are not swinging something at the end of an arc, we can't really make the racket go straight...but we do try. It's important to note that the maximum power of the lever system the player has to work with is at 90 degrees to the line from the shoulder/left foot that is the fulcrum of this lever system to the contact point. Your body has done all this work to get the racket head to move in the right direction at the point of contact. Now to hit with any real force, you have to RELEASE the racket head through the ball. If you hold on too tight or swing too hard, you will keep the racket head moving in that circle. The tangent force to an item swinging in a circle is going perpendicular to the radius/the arm and racket and just at impact that tangential force (perpendicular to the centrifugal or centripetal force, I always get confused which one it is in or out) needs to be released to the target. (Imagine a David's sling releasing that stone at Goliath.)

I don't see anything wrong with what you are saying, but the point I was trying to make is that the linear force of a square stance forehand or backhand, for that matter, is a small part of the power that is used to hit the ball. The player is trying to generate a linear transfer of force at the end of a rotational movement he is using to create that collision. (Sounds pretty complicated. Must be a hard game!) It's kind of like saying I'll put a baseball on a tee and let you hit it with a regular swing or if you want you can get together with 3 friends and pick up a log and run straight at the ball with the log and see if you can transfer more momentum to that ball running that big package of momentum at the ball. You'll be coming at that ball with a shitload of momentum, but the ball isn't going to go very fast. I'll take the regular swing. Sounds riduculous, but that's the essence of the difference between saying you hit a square stance forehand with mostly linear momentum from the weight transfer as opposed to the angular momentum you use on every swing!

Gotta go. Looking forward to your response. And I wish a couple of biomechanists who would know what they are talking about. We may have to take this out to a separate thread.

don brosseau

[uspta2753242588]

This discussion reminds me of:

http://ca.youtube.com/watch?v=svDFoBHzM1A

[tennis_chiro]

Don't cop out. Take your time. It's not that complicated

This discussion reminds me of:

http://ca.youtube.com/watch?v=svDFoBHzM1A

Point well taken. This is about physics and mathematics and it is not entirely intuitive. But read my examples a little more carefully. They are not that complicated. And the point is that whatever the forces we want to generate, the body is limited to using torques to generate those forces. Even as simple a motion as pushing something in a straight line with one limb is generated by some muscle in your body shortening its length to move a bone and exert a force through a lever; even if the motion looks like a straight line. When you put a stick or a racket in your hand, you are multiplying your force by lengthening the lever arm. The laws of pulleys and levers apply. Stepping into a ball could add 5, maybe even 10 mph to a shot; but relative to a 60 mph groundstroke or a 120 mph serve, that's not much. In fact, depending on what part of the body you are talking about, at the moment of impact, the body might not be moving forward at all. In fact, we are often talking about the necessity of hitting the ball moving backwards...even in a square stance.

Anybody else??
don

[uspta2753242588]

Sorry, I was really just having fun with a clip people send me on a nearly weekly basis – a parody of my work if you will – I find it quite funny. I promise to brush up on my math and physics so I can follow the mechanical logic in this thread, some of which escapes me at this time. Perhaps I’ll provide specific examples later if my workload decreases.

In the meantime, as I understand it, this thread is about the degree to which different forehand stance options use the different forms of momentum and addresses the long held view that some stances use one form to the virtual exclusion of the other. This was hashed out elsewhere and my take was (Linear Momentum was assessed as motion of the body center of mass – CM):

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“… in my applied and basic research I systematically calculate momentum generation and flow based on 3D data analysis. On the forehand (open, neutral, square, closed, or otherwise) angular momentum of the racquet relative to the CM is the critical entity in racquet head velocity.

This implies generation and transfer of angular momentum, by and through the body respectively, is a critical issue in forehand stroke production for all stance permutations. These parameters vary by stroke stance technique (demonstrably) and illustrate interesting contrasts among the various stance approaches.

Linear momentum of the system (player+racquet) is of course present on all forehands to varying extents. It is not possible to determine motion of the system CM by looking at a video. Its direct impact on racquet head speed is negligible in any stance approach. That should not be construed as a statement about its importance.

From a kinetic perspective, linear momentum can be used to generate angular momentum via ground forces. It also enhances angular momentum generation by allowing the leg muscles to be primed (pre-contraction, contraction velocity, and SSC) for contraction.

But the importance of linear momentum of the system is not confined to angular momentum generation. It also has implications to the transfer of angular momentum to the racquet. This transfer, occurring at the joints, can be enhanced if the muscles crossing the joints are allowed to contract in slower, isometric, or eccentric conditions. Such is the case with proper linear manipulation of the CM (velocity or momentum), manipulation that may simply be a resistance to non-beneficial motion tendencies.”

--------------------------------

I can’t determine if this fits in here, but it seemed to help the previous discussion of the “momentum type” domination traditionally attributed to the various stance options. - Brian

[uspta146749877]

For uspta275324588

Hi,
I started a thread under the following title
"Forehand stances and tactical considerations"
I was hoping to get some comments about tactiical considerations.

Linear and angular momentum is of less interest to me.
If you can help on this topic I would appreciate it,
regards,
julian usptapro 27873

[BrianGordon]

Hi,
I started a thread under the following title
"Forehand stances and tactical considerations"
I was hoping to get some comments about tactiical considerations.

Linear and angular momentum is of less interest to me.
If you can help on this topic I would appreciate it,
regards,
julian usptapro 27873

Well… your title did mention tactics but roughly 13 of the 16 bullet points seemed to address stroke mechanics and directly or indirectly referenced momentum generation, utilization, or related concepts. The subsequent discussion also seemed to be mechanics oriented but I apologize to the masses if I posted off topic.

Anyway, with regard to stance implications to tactics I guess it depends on the tactical elements you are wondering about. It seems to me that the movement tactics consequences of the stance approaches have been addressed ad nauseam.

A more interesting question to me is shot execution tactics in dealing with a wide variety incoming shot and positional possibilities. Here I would submit, and have found some evidence, that the particular stance used for a given shot is (or should be) individually tailored based on other more consequential aspects (upper body/arm mechanics) of one’s chosen or evolved base mechanics package. These aspects have inherent and unique strengths and weaknesses IN GIVEN SITUATIONS that can be facilitated or compensated by the specific advantages that different stance options provide.

Sorry to sound like the video I linked, but in other words, each individual must find the correct stance, for each specific situation, in the context of the rest of their stroke mechanics attributes – by this logic, a cookie cutter answer to your question is not possible, and even a reasonably coherent description of broad classifications is well beyond the scope of a forum post.

[uspta146749877]

For Brian Gordon

Thank you
julian

[tennis_chiro]

no cookie cutter answers

Julian,
I probably ought to apologize for pushing the thread toward the angular momentum/linear momentum question. I just get upset when I see that particular line of thinking put forward, ... but

in response to your more direct question, I think Brian is on the money. There is too much of an effort to say you use a certain motion in a certain situation.

Whether it is a open, square, or semi-open stance, the shoulders have to go through ALMOST the same turn. Open stances definitely allow you to get back into the court quicker. Sometimes you just don't have time to get your feet around into a square stance even if that is your preferred stance. If you are trying to hit an approach that leads you to the net, it is easier to move out of a closed stance or even semi-open stance, by swinging the rear foot forward immediately upon completing the follow through for the approach (planting on the front foot), whereas the open stance might actually end up throwing you a little bit back...it's almost as if you need a drop-step. On the other hand if you are exploding on that short ball and won't need another shot as is often the case in today's game, it doesn't matter all that much.

You are going to tie a player up in knots if you try to get him to adopt a certain stance, depending on the ball or the tactic. He needs to use his best shot and think about moving the racket into position behind the ball so he can execute that shot. If you are working on developing a particular shot and hitting it well requires a certain kind of foot work, then you can work on that footwork. But if the idea is to load a different type of footwork into the computer depending on the tactical intent of the shot, you are going to crash the computer. I really try to get my players to learn to move the racket head into position behind the ball and let their body figure out what to do with their feet subconsciously. Sometimes I have to help them out a little bit by making them catch the ball with the racket to feel themselves getting into position, but you definitely have to get them away from running their bellybuttons to the ball and ending up out of position to execute their intended shot.

Some players hit the ball really well with an open stance. Others hit almost everything square (rare these days), but you can't choose the stance depending the tactic. The player has to hit his best shot whenever he can. If time is at a premium, he's probably going to have to hit semi-open or open stanced.

don

[llll]

my coaches have taught me to use a neutral stance when coming foward on an approach shot and hit as i am coming foward. this stance lands itself to that pupose for me. cant say if its because of linear or angular momentum

[llll]

in response to above posts if you train to hit approach shots with neutral or closed stances doesnt that teach the player the footwork to get there in such a way to be able to use that stance? most players when presured do what they have to do to get the ball back and try to neutralize the situation. in those circumstances the player is thinking get the ball back not what stance am i using. are you asking should certain stances be trained for certain situations?