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SeasonedNovice
10-01-2011, 05:10 PM
Is it "By-The-Book" to be off the ground (AKA Jumping) while at the apex of your serve?


I always do, however yesterday a friend was giving me a lecture about how much energy you LOSE while not having your feet on the ground at contact, and says the pros don't jump (yeah right).

Any thoughts?

rjw
10-01-2011, 05:35 PM
If you are in good enough shape to get off the ground , then go for it, especially if you're getting more weight into the serve.

Seems like a no brainer to me

vincent_tennis
10-01-2011, 06:15 PM
the pros dont jump intentionally, nor have the idea of "jumping" in their mind

They only lift off the ground due to the amount of energy they put into the ball

rkelley
10-01-2011, 06:50 PM
Is it "By-The-Book" to be off the ground (AKA Jumping) while at the apex of your serve?


I always do, however yesterday a friend was giving me a lecture about how much energy you LOSE while not having your feet on the ground at contact, and says the pros don't jump (yeah right).

Any thoughts?

Your friend is wrong. If one was trying to throw a shot put then keeping one's feet on the ground would yield the best throw, but serving is different. The goal for serving is the get the highest racquet head velocity at impact. There are many joints between the racquet head and the feet. The server is trying to whip the racquet head into the ball. The racquet's weight and the ball's weight are important too. Jumping, ground force reaction, whatever, increases racquet head speed.

That said, I've seen some commentary by knowledgeable folks that say that jumping only adds about 15% to your serve. Most of the power comes from the rotation of your core. Still, and extra 15% is worth it.

Also consider that just about every pro, male and female, is well off the ground at contact on the serve.

Bartelby
10-01-2011, 07:10 PM
I think the weight of the shot keeps you on the ground, whereas in the javellin they do lose contact with the ground.

Power Player
10-01-2011, 07:10 PM
Only 15%? That is a ton of a difference.

baek57
10-01-2011, 09:34 PM
Yep. "only" 15% is like a 15mph difference/improvement.

Devilito
10-01-2011, 09:41 PM
Of course you jump, but maybe your friend has the wrong idea due to watching bad casual players on a public court that have odd looking mechanics. You don't jump UP to hit a serve like a vertical leap. When you serve you use the back-forward momentum and jump IN to the shot giving you increased power, spin and consistency.

rjw
10-01-2011, 09:53 PM
you don't jump UP to hit a serve like a vertical leap. When you serve you use the back-forward momentum and jump IN to the shot giving you increased power, spin and consistency. This is tennis 101 here. I'd stop taking tennis advice from your friend if i were you.

Kind of obvious, but the pros are in the air on almost every shot

NLBwell
10-01-2011, 09:56 PM
No, jumping will not add 15% to your serve, or anywhere close to that. Several of the above posters are right, the energy of your motion lifts you off the ground. Maybe you could say a 15% better serve would lift you off the ground. Pretty much all pro's get significantly into the air (Also, being higher will give you a better angle into the court, but that is a second-order effect).

mistapooh
10-02-2011, 12:27 AM
the pros dont jump intentionally, nor have the idea of "jumping" in their mind

They only lift off the ground due to the amount of energy they put into the ball

I can't believe this is still myth is still alive.

http://www.youtube.com/watch?v=k0AXyjMVkKY

goran_ace
10-02-2011, 12:56 AM
jumping/cathcing air during the service motion is a side effect of exploding off your legs into the serve; it is not something you consciously try to do

purge
10-02-2011, 12:59 AM
i suppose the original confusion of your friend stems from false application of some basic theories of physics.

the physical agrument for losing power when your feet are off the ground is the eimply aktio = reaktio wich means that when you hit the ball it creates 2 forces, one pushing the ball forward and the other pushing you backwards.

the classic example is the cannon on wheels firing a cannonball. when it fires not only does the cannonball fly away but the cannon also rolls backwards quite some way. this energy that pushes the cannon back is obviously lost to the pace of the shot. if the cannon was firmly placed on the ground that force would be fully absorbed and go completely into the shot which would make it considerably faster.

but that is only a factor if both objects have a considerable mass as the the forces are split according to the realive masses of the objects involved. and in the case of a shot in tennis the mass of the tennisball compared to that of the player is completely neglectable. the fraction of force that goes into pushing the server back is not noticable at all.

one more thing about the jumping.. its not only a result of trying to push your weight into the shot its also a means of getting the highest possible contact point obviously since it will give you the best possible angles for your serve. a 6 foot person who jumps into his serve will thus be able to hit a serve like a 6'1 or 6'2 player who doesnt. thats a big advantage as well

bottom line..
JUMP JUMP!!!
dont this **** make a ***** wanna..

listen to busta rhymes he knows his tennis ;)

rjw
10-02-2011, 02:43 AM
rephrase to 'go airborn'

vincent_tennis
10-02-2011, 02:49 AM
I can't believe this is still myth is still alive.

http://www.youtube.com/watch?v=k0AXyjMVkKY

No one does it on purpose damnit -_-

jumping/cathcing air during the service motion is a side effect of exploding off your legs into the serve; it is not something you consciously try to do

Thank you.

SystemicAnomaly
10-02-2011, 03:11 AM
...

I always do, however yesterday a friend was giving me a lecture about how much energy you LOSE while not having your feet on the ground at contact...

With badminton jump smashes, most players will not get as much power on their shots as with their ground-based smash. Badminton players will usually jump in order to hit at a steeper angle (over a 5 foot net) rather than added power on the shot. However, the mechanics and the timing of the badminton jump smash is different than that of a tennis serve.

While jumping up & forward on the tennis serve can result in more advantageous contact point (higher & closer to the net), it is not usually the primary reason for leaving the ground. Tennis servers jump because they are adding leg drive to their serve for a more effective kinetic chain.

A minor or moderate leg drive may not cause the server to leave the ground. However, a more generous leg drive will. The legs start their upward drive as the racket head drops from the trophy position. When the legs are fully extended, the racket head will be at its lowest point in the drop and will start to mover upward. Correctly timed, the legs drive upward will be followed by the racket arm extends upward.

I've seen claims that the leg drive adds about 15-20% more power or RHS to the serve. It actually seems like more. It could be that the greater leg drive makes the mechanics of the serve more efficient and easier on the shoulder and other parts of the body. You really don't want to generate most of your serve power with your shoulder and arm. Better to employ a more complete kinetic chain.

Andre D
10-02-2011, 03:42 AM
you don't jump UP to hit a serve like a vertical leap. When you serve you use the back-forward momentum and jump IN to the shot giving you increased power, spin and consistency. This is tennis 101 here. I'd stop taking tennis advice from your friend if i were you.

what about the up the mountain advice by pat dougherty? so we jump up or forward?

mistapooh
10-02-2011, 04:02 AM
No one does it on purpose damnit -_-



Thank you.



jumping/cathcing air during the service motion is a side effect of exploding off your legs into the serve; it is not something you consciously try to do

Stop confusing people with saying "don't jump," this has been beaten to death. Saying "exploding off your legs" is essentially saying to spring/ aka JUMP. Yes, your leg drive starts the kinetic chain, start researching from there. Yes, you consciously do it or else you wouldn't have a good looking service motion. No, your 12 oz racket and whip of your arm didn't magically propel your whole body into the air.

Bottom line: bend your legs to "spring" into the ball, don't serve like a badminton player.

http://www.youtube.com/watch?v=Wkah8U1GQ_k

netguy
10-02-2011, 09:38 AM
Every shot in tennis comes from the interplay of seven joints:
Ankle, knee, hip, shoulder, elbow, wrist and neck.
In serving or any other shot, taking the fisrt step,(ankle bending), in the right direction is key...
Try to serve without bending the ankle, or with most of your weight on your heels, and you'll see how dull and ineffective your serve will become. In fact, ankle bending is the most important step because it roots you to the ground, helps to balance and align your whole body, and launches you into the air by pushing from the front part of your sole against the gound. All the other joints should follow naturally.

TennisCJC
10-05-2011, 10:38 AM
Yes, jump, push off, spring with legs - a rose by any other name.

At least get up on the balls of your feet if you don't leave the ground. I think getting on balls of feet or airborne is the desired goal. It also relives pressure and twisting on the ankles.

Dolgopolov get several inches off the ground when he serves. US Open commentators were remarking on how high he gets off the ground. He seems a bit extreme but most pros get off the ground a bit.

LeeD
10-05-2011, 10:45 AM
OK, lots of info here...
Another take, from as usual, a different angle...
RAISE YOUR CONTACT POINT, giving you a much better angle to get your serves IN, while you have the energy to do so. Once you hit 62, you LOSE that energy you had when you were younger, and CANNOT raise your toes 9" off the tarmac like you did when you were young.
If you aren't jumping to serve now, you will NEVER get another chance later.

rufus_smith
10-05-2011, 03:59 PM
Not sure a jump it is very necessary. You can look at serve videos of old timers. Pancho Gonzales didn't jump. Roscoe Tanner didn't jump. They hit huge. Young McEnroe lifted maybe 3 inches up and forward at most but that was to charge the net faster. Most modern pros do jump though.

toly
10-05-2011, 05:11 PM
About jump you can also read old thread http://tt.tennis-warehouse.com/showthread.php?t=382481

LeeD
10-05-2011, 06:24 PM
Pancho wasn't allowed to jump.
Tanner got off the ground an easy 6".
Mac you might be right, but who wants HIS serve?

Mongolmike
10-07-2011, 11:00 AM
I've been trying to copy a pic of me serving in my last tournament... I'm 53 and slightly overweight, but the pic clearly shows me off the ground on my serve and it looks like my serve propelled me rather than just a common jump.

Anyone know how I can transfer a Facebook pic to this thread? I tried a simple right clip copy, its a JPEG, but it didn't work. I'll try a link...

http://www.facebook.com/pages/Towpath-Tennis-Center/135147559188?ref=ts&sk=photos#!/photo.php?fbid=10150275719814189&set=a.10150275717809189.348705.135147559188&type=3&theater

but that doesn't look like it'll work either. I can serve, I just can't manipulate computer photos! (Edit: HEY! It worked! Whoo-whoo!)


My partner is younger than me, and does not elevate on his serve, but I do on my first and my 2nd serves (kicker). Also, I'm a USTA 3.0 and will/should probably bump up to a 3.5

dlam
10-07-2011, 08:29 PM
I dont consciously think jump but I do get off the ground.
It more like springlike action for my legs.
I have a pinpoint serve so I like to bring my trail foot towards my front foot .
My upperbody is leaning toward the court during the serve motion,
My ball toss is in front of me and if I toss is too far then I have to "spring" into the shot
ideally I like to keep my toes on the ground.

But if I have to err than I rather err to a bit farther forward so that momentum can propel me into the court, if the ball is too close to my body then my im flat footed and I lose momentum and rhythm, the ball likely ends up into the net.

Macedo
10-08-2011, 01:33 PM
I have a nice jump it seems, but I don't have any consistency in my serve ):
http://www.facebook.com/media/set/?set=a.1349398147384.2044374.1604256101&type=3#!/photo.php?fbid=1066000942631&set=a.1349398147384.2044374.1604256101&type=3&theater

charliefedererer
10-09-2011, 09:46 PM
Is it "By-The-Book" to be off the ground (AKA Jumping) while at the apex of your serve?


I always do, however yesterday a friend was giving me a lecture about how much energy you LOSE while not having your feet on the ground at contact, and says the pros don't jump (yeah right).

Any thoughts?

Tell your friend he doesn't know what he is talking about.

Have him check out this video:
http://www.youtube.com/watch?v=ajoZ0f7hw-A

toly
10-10-2011, 08:20 AM
In racquetball players never jump. The fastest racquetball serve was recorded by Egan Inoue. He served it at 191 miles per hour.
See please http://www.5min.com/Video/Learn-how-to-Play-Racquetball---Serves-140309204
In all other sports (except tennis and volleyball), athletes have never jumped into the air before the stroke or throw. Why not?

Manus Domini
10-10-2011, 08:25 AM
From another thread:

The jump is not just unimportant, it's bad. Don't jump. Instead, let your kinetic chain throw you above the ground (that's how I think of it), starting with your legs, going next to your hips and shoulder turn, and finishing with your arm. You shouldn't consciously "jump", rather you should propel yourself into the ball, and if that means leaving the ground, do so.

maggmaster
10-10-2011, 08:49 AM
Maybe I am mistaken but is it even possible to "jump" from the appropriate knee bend position? I get off the ground but it is not a jump, not like a rebound or a header. The best motion that I can compare it to is the powerclean hop to get under the weight.

rkelley
10-10-2011, 08:57 AM
In racquetball players never jump. The fastest racquetball serve was recorded by Egan Inoue. He served it at 191 miles per hour.
See please http://www.5min.com/Video/Learn-how-to-Play-Racquetball---Serves-140309204
In all other sports (except tennis and volleyball), athletes have never jumped into the air before the stroke or throw. Why not?

Tennis players only jump on their serve and sometimes on the forehand. There's are specific reasons why the physics of those strokes, the racquet, and the way the human body works combines to make jumping the optimal way to generate power. On the serve, the spins that a tennis player needs to use to keep the ball in even on the "flat" serves, the use of the continental grip over an EFH grip, as well as gaining height for margin over the net, probably also play a part.

Also the fact remains, just about every high level player jumps on their serve. Most, when they have the time to set-up, jump into their forehands if they're trying to get maximum power. Are all of those athletes using sub-optimal technique?

I think there's quite a bit of jumping in badminton to generate power. I don't know if volleyball is quite the same. Think the jumping there is primarily to gain height over the net, but honestly I'm not sure. The ball is a lot heavier, and the player is only using their arm (i.e. no racquet), so it's different than tennis.

Manus Domini
10-10-2011, 09:18 AM
Tennis players only jump on their serve and sometimes on the forehand. There's are specific reasons why the physics of those strokes, the racquet, and the way the human body works combines to make jumping the optimal way to generate power. On the serve, the spins that a tennis player needs to use to keep the ball in even on the "flat" serves, the use of the continental grip over an EFH grip, as well as gaining height for margin over the net, probably also play a part.

Also the fact remains, just about every high level player jumps on their serve. Most, when they have the time to set-up, jump into their forehands if they're trying to get maximum power. Are all of those athletes using sub-optimal technique?

I think there's quite a bit of jumping in badminton to generate power. I don't know if volleyball is quite the same. Think the jumping there is primarily to gain height over the net, but honestly I'm not sure. The ball is a lot heavier, and the player is only using their arm (i.e. no racquet), so it's different than tennis.

They don't jump, they accelerate upwards. Huge difference.

They don't consciously think "I'm going to push off my legs to get high up", they think "I'm throwing my body upwards and forwards" and that's why they leave the ground.

rkelley
10-10-2011, 09:33 AM
They don't jump, they accelerate upwards. Huge difference.

They don't consciously think "I'm going to push off my legs to get high up", they think "I'm throwing my body upwards and forwards" and that's why they leave the ground.

A rose by any other name . . .

I understand what you're saying. A player isn't focusing on jumping as high as they can, but the fact remains they jump. If you "throw you body upwards" the result is going to be that your feet are going to leave the ground. That's a jump.

Manus Domini
10-10-2011, 12:36 PM
A rose by any other name . . .

I understand what you're saying. A player isn't focusing on jumping as high as they can, but the fact remains they jump. If you "throw you body upwards" the result is going to be that your feet are going to leave the ground. That's a jump.

Err, you're actually wrong.

Jump means "to leap or spring clear of the ground or other surface by using the muscles in the legs and feet", but you aren't just using the legs and feet in the serve. You are using your feet, legs, hips, shoulders, arms, and wrists. In fact, leave the ground using only your legs and feet, and leave the ground using your hips, shoulders, and arms as well. Feel the difference?

I hear what you're saying, but for people who are just learning the serve, hearing the word "jump" will set a really bad image in their minds. They'll think about jumping instead of naturally leaving the ground (I still do sometimes), which causes inconsistency, inefficiency, and weaker serves.

rkelley
10-10-2011, 01:16 PM
Err, you're actually wrong.

Jump means "to leap or spring clear of the ground or other surface by using the muscles in the legs and feet", but you aren't just using the legs and feet in the serve. You are using your feet, legs, hips, shoulders, arms, and wrists. In fact, leave the ground using only your legs and feet, and leave the ground using your hips, shoulders, and arms as well. Feel the difference?

I hear what you're saying, but for people who are just learning the serve, hearing the word "jump" will set a really bad image in their minds. They'll think about jumping instead of naturally leaving the ground (I still do sometimes), which causes inconsistency, inefficiency, and weaker serves.

I think we agree here. Let's leave the definition of the word "jump" to linguists.

When I taught my kids to serve I didn't tell them to jump for exactly the reason you say. I told them bend their legs and explode toward the ball. This is exactly what I think when I serve too. Call it a jump, call it GFR, levitation, whatever. The server's feet aren't touching the ground when the ball is hit.

Manus Domini
10-10-2011, 02:22 PM
I think we agree here. Let's leave the definition of the word "jump" to linguists.

When I taught my kids to serve I didn't tell them to jump for exactly the reason you say. I told them bend their legs and explode toward the ball. This is exactly what I think when I serve too. Call it a jump, call it GFR, levitation, whatever. The server's feet aren't touching the ground when the ball is hit.

Regardless of the meaning of "jump", this is a "Tips/Instruction" thread, so I don't think the word should be used at all here. Last thing we want is a new player to casually read this, but not in depth and not understanding what this is about, and being like "well, RKelley wrote in one of the threads you have to jump" or something :)

toly
10-10-2011, 04:24 PM
i suppose the original confusion of your friend stems from false application of some basic theories of physics.

the physical agrument for losing power when your feet are off the ground is the eimply aktio = reaktio wich means that when you hit the ball it creates 2 forces, one pushing the ball forward and the other pushing you backwards.

the classic example is the cannon on wheels firing a cannonball. when it fires not only does the cannonball fly away but the cannon also rolls backwards quite some way. this energy that pushes the cannon back is obviously lost to the pace of the shot. if the cannon was firmly placed on the ground that force would be fully absorbed and go completely into the shot which would make it considerably faster.;)

This is true.


but that is only a factor if both objects have a considerable mass as the the forces are split according to the realive masses of the objects involved. and in the case of a shot in tennis the mass of the tennisball compared to that of the player is completely neglectable. the fraction of force that goes into pushing the server back is not noticable at all.;)

This is incorrect.

Before we start accelerating the ball we should accelerate our arm and racquet with mass around 20 pounds. As result we create very big forward momentum 20pounds*50mph. If we stand on the ground we can transfer this momentum (force) to the mass of the Earth. Thus, our body still is able to rotate forward without any problem.
Suppose we jumped before contact. Then, according to one of the fundamental laws of physics – Conservation of Momentum, if one part of the body (arm) is given a forward momentum, then some other part of the body (torso) simultaneously be given exactly the same momentum in the opposite direction (backward). But usually our arm is connected to torso, thus our arm also get some significant momentum directed backward. Thus, we inevitably will lose racquet/ball’s speed.
The jump into air before impact cannot increase serve power, quite the contrary!!!:confused:

rkelley
10-10-2011, 09:26 PM
Before we start accelerating the ball we should accelerate our arm and racquet with mass around 20 pounds. As result we create very big forward momentum 20pounds*50mph. If we stand on the ground we can transfer this momentum (force) to the mass of the Earth. Thus, our body still is able to rotate forward without any problem.
Suppose we jumped before contact. Then, according to one of the fundamental laws of physics – Conservation of Momentum, if one part of the body is given a forward momentum (arm), then some other part of the body (torso) simultaneously be given exactly the same momentum in the opposite direction (backward). But usually our arm is connected to torso, thus our arm also get some significant momentum directed backward. Thus, we inevitably will lose racquet/ball’s speed.
The jump into air before impact cannot increase serve power, quite the contrary!!!:confused:


Toly, this discussion has come up before and maybe I should just let it go, but I am concerned that since you are applying physics to support your arguments that someone might be convinced that you are correct. Respectfully, I don't believe you are correctly analyzing the physics involved in hitting a serve and, as I've mentioned before, your analysis would require that just about every high level player hits their serve in a sub-optimal way.

The key to this whole analysis is that the goal of getting the maximum velocity on the ball during a serve is to get the maximum velocity of the head of the racquet at impact. The velocity of the center of mass of the racquet, the arm, or any part of the body doesn't matter. It's just the velocity of the head of the racquet that matters. You also have to take into account how the human body is built and how our joints work.

Here's a link to Federer hitting a serve in super slow motion:
http://www.youtube.com/watch?v=InYd8IrFnkU

At about 0:26 he's in the trophy pose and starts to push with his legs. The vector of his leg push is almost totally up. It has a small component into the court, but it's almost all up. Note the path that the right arm and the racquet takes while this is happening. His upper arm is not going forward, it's going up also, about in line with the leg push. In fact his upper arm moves about 180° around his shoulder. At 0:26 his elbow was pointing down and the racquet was pointing up. At 0:31 the elbow is pointing up the racquet is pointing down. His upper arm is rotated back about as far as it can go without injury and his wrist is also supinated back about as far as it can go.

All the force from his legs pushing up has gone into getting his arm and wrist into this position. His legs are driving his whole body up towards the ball. The racquet has not started to come forward towards the ball.

The other place where he's using the reaction force from the ground is to start his core rotating. But note that his shoulders aren't level with the ground. His core is rotating about an axis that's about at 45° to the ground. His left shoulder was high and his right shoulder low at 0:26. Before his feet leave the ground at 0:31 his shoulders have started to trade places. By 0:32 his right shoulder will be high and his left shoulder low. His feet's contact with the ground help react the force generated by rotating his shoulders.

Also note how his left arm aids in the process of bringing his shoulders around more powerfully. The arm starts coming down at 0:26 also. The left arm coming down will tend to un-weight his feet. The leg push and the left arm motions are complimentary. The shoulder rotation is complete after his feet are completely off the ground, but the contribution of his left arm helps the motion.

At about 0:31, his feet have left the ground, so he's not going to get anymore benefit from pushing on mother earth. He has used all of his leg force to drive his body up, get his right elbow high, his wrist supinated (so consequently his racquet is cocked down), and to start his shoulder turn. His left arm has assisted in this process but has done about all that it can do.

The racquet face has still not begun to come forward towards the ball. The whole racquet will travel up towards the ball until 0:32. However because of the way a human arm works he has stored an incredible amount of energy. Everything that he's done up to this point was about storing energy. He has loaded the spring. He is now in the position to unleash that energy onto the ball.

From 0:32 to 0:34 the racquet comes forward into the ball. His arm whips up and into the ball with the racquet still lagging behind. Only when his arm is mostly extended does the whip get cracked and the racquet come around into the ball. Of course as the racquet comes forward something has to react this force. His feet have long since left the ground so he's not getting any help there. What reacts the racquet's forward velocity is the lean into the court that Federer had when he started his upward motion (the small component of leg push into the court), and the motion of his legs. Remember, the only thing that matters is how fast the head of the racquet is going. Every other part of his racquet and body can be going backwards (in theory anyway). In this video he's really bringing his knees up. Usually it's a bit more of a scissoring action between the right and left leg. Here's another video that shows that:

http://www.youtube.com/watch?v=vcjZ5r_YHV0

He's 180 lb human reacting a 12 oz racquet. He doesn't need that much force to react the racquet. This is the area that you've been focusing on, but you're missing the forest for the trees. What he has done by driving up towards the ball instead of staying in contact with the ground and moving forward is help load energy into the rest of his body and unleash that energy as quickly and as violently as possible onto the ball. In that last instant when the racquet finally does come toward the ball he can react the motion with other parts of his body. If he were to keep his feet on the ground as you prescribe then it would not be possible for him to as completely load up all of this energy into his joints. He could better react the force of the racquet going forward, but he would do so at the expense of completely loading all of the energy that he was able to load by pushing up rather than forward.

Sorry for the book, but I hope this makes sense.

Chas Tennis
10-11-2011, 12:34 AM
Basic Reference. This B. Elliott reference discusses these important subjects: serve, leg thrust, stretch shortening cycle, internal shoulder rotation. It claims that 40% of the racket head speed results from internal shoulder rotation.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2577481/

(If unclear of any terms search each on the internet. It is also good to always keep in mind that muscles, like ropes, only pull. )

Stretch Shortening Cycle History. Starting in the 1960s and continuing until the 1980s, Eastern Europeans were the first to appreciate and scientifically apply the stretch shortening cycle as well as drugs and scientific athlete selection methods.

Look at the Summer Olympics gold medal totals for each Olympics.

http://en.wikipedia.org/wiki/East_Germany_at_the_Olympics

US Summer gold medals each Olympics -

http://en.wikipedia.org/wiki/United_States_at_the_Olympics

More Summer gold medals to East Germany (population 18 million) than to the US in 1976 & 1988.

The East Germans understood the stretch shortening cycle among other things.

Is Stretch Faster? I’m a little uncertain of my interpretation - but the tennis book by D. Knudson, [U]Biomechanical Principles of Tennis Technique, seems to say that a muscle that is stretched may be inherently able to shorten faster than one that is simply shortening by deliberate muscular contraction. If true, then for the fastest motions you want to have the participation of muscles that shorten from a stretched position as well as from deliberate muscular contraction.
http://www.amazon.com/dp/0972275940?tag=thetennisserver&link_code=as3&creativeASIN=0972275940&creative=373489&camp=211189

What the leg thrust does in my opinion. The leg thrust functions to stretch the internal shoulder rotators, mostly the pec & lat both of which attach on the front of the upper arm. (Search internal shoulder rotator muscles.) In the service motion the upper arm extends approximately straight out from the shoulder joint throughout the motion. Just before the leg thrust the elbow is bent at about 90° and also the racket is roughly in line with the forearm. This forearm-racket configuration creates a large moment of inertia. Therefore, when the legs thrust up the forearm-racket lags behind and externally rotates the shoulder. This adds stretch to the internal shoulder rotators (by external shoulder rotation). The internal shoulder rotators - now a coiled spring - are brought up by bending the trunk to raise the hitting shoulder. The stretched internal shoulder rotators unwind ( in ~ 0.03 second*) to rotate the upper arm and powerfully accelerate the racket head because the racket is then at an angle, β, to the semi-straight arm.

(Simplifying terms such as 'loading', 'energy flow', 'kinetic chain', etc., that are not explained leave out a lot of the detail with regard to the muscles involved and their motions.)

For more serve discussions, especially those by Toly with illustrations of β, see the thread below.

http://tt.tennis-warehouse.com/showthread.php?t=370729&

Also, see Roddick comment on legs in video from Mistapooh reply #18. http://www.youtube.com/watch?v=Wkah8U1GQ_k

* Internal shoulder rotation for a pro serve took about 7 frames at 240fps ~ 0.03 second. 7/240 = 0.03 second.

Rob.D
10-11-2011, 01:58 AM
On the topic of momentum-transfer, it shouldn't make any difference if you jump or not. If jumping increases your racket head speed then yes you will hit a faster serve. But if both the jump and no jump were to produce the same racket head speed then being stood on the ground or in the air won't affect the momentum transfer to the ball. Being "fixed" to the floor doesn't mean that you will transfer more energy to the ball.

Rob

rkelley
10-11-2011, 08:23 AM
But if both the jump and no jump were to produce the same racket head speed then being stood on the ground or in the air won't affect the momentum transfer to the ball. Being "fixed" to the floor doesn't mean that you will transfer more energy to the ball.

Rob

Actually I don't believe this is completely correct.

If we assume that the server's body is a completely passive mass, which is a really bad assumption, then there would be a slight benefit for the server being fixed to the ground when the racquet impacts the ball. At impact there is going to be be a reaction on the racquet, and therefore the server, in the opposite direction of the ball. If the server is fixed to the ground then the ground can react this force. If the server is in the air the server's body will have a small momentum change backward equal to the momentum change forward of the ball. When the server's in the air there are no external forces on the server's body other than when the racquet contacts the ball, so momentum of the server/ball system must be conserved.

I believe this is the issue that some folks are really focused on and it's correct as far as it goes.

However the server is not a passive mass. The server is capable of moving in many different ways, even in the air. At impact, if the server is in the air, the server can bend slightly at the waist. Since the server isn't touching the ground the server's center of mass cannot be affected by this motion. The bending at the waist will cause the upper and lower body to come forward and the waist/rear-end to go back. The upper body will also come down a bit and the lower body to come up since they are connected. The motion of the upper body coming forward will tend to add velocity to the racquet and can react the force of the impact of the ball with the racquet. The sever's center of mass must react backward with the overall momentum change, but as long as the racquet is driven forward into the ball, the fact that the server's center of mass has reacted backward doesn't matter. The server kicks a foot forward and it's all good.

And, if the server tried this trick of bending at the waist at impact while standing on the ground I don't think it would work very well. The server's feet are not actually fixed to the ground. The connection to the ground is only through friction, which requires a normal force. If he pulls his feet up, as bending at the waist would tend to do, he will start to un-weight his feet. Un-weighting his feet will reduce is normal force and thereby reduce the maximum frictional force that his feet can react parallel to the ground, but he will be increasing the required frictional force because he's trying to bend at the waist to create more force at the racquet. It doesn't seem like it will work.

toly
10-11-2011, 09:54 AM
Thank you for the effort, rkelley, but unfortunately you didn’t convince me.
Can you just explain why in most sports, athletes have never jumped before stroke or throw?:)

LeeD
10-11-2011, 10:07 AM
Maybe in most sports, like javelin throwing, baseball, QB throwing, rock skipping, or frisbee throwing, there is no advantage of a HIGHER STRIKEPOINT!
Notice in volleyball serves, they always jump!
When you need to shoot over an opponent in now defunct basketball, you JUMP SHOOT!
Higher strikepoint, or contact point, is the key to the whole thread. But you don't need to believe it, just because I pointed it out.
You may serve underhand, from your ankles, and play tennis your way.

toly
10-11-2011, 10:24 AM
Maybe in most sports, like javelin throwing, baseball, QB throwing, rock skipping, or frisbee throwing, there is no advantage of a HIGHER STRIKEPOINT!
Notice in volleyball serves, they always jump!
When you need to shoot over an opponent in now defunct basketball, you JUMP SHOOT!
Higher strikepoint, or contact point, is the key to the whole thread. But you don't need to believe it, just because I pointed it out.
You may serve underhand, from your ankles, and play tennis your way.
I do not ask why in some sports athletes jump. My question is: Why in most sports, athletes have never jumped before stroke or throw?
If jump can increase power, they must jump.:)

LeeD
10-11-2011, 10:29 AM
geez, because in most other sports, THERE IS NO ADVANTAGE gained by jumping!
A baseball player doesn't strike out more batters by raising his release point. You might cite RandyJohnson (6'10"), but his advantage is the longer lever with a LOW release point.
Think of the sidearmer's in pitching.
In VOLLEYBALL, there is an advantage in raising the release point, just like in tennis.
I don't think you can serve faster by jumping, but your TARGET is bigger when you raise your strikepoint.

Rob.D
10-11-2011, 10:46 AM
Actually I don't believe this is completely correct.

If we assume that the server's body is a completely passive mass, which is a really bad assumption, then there would be a slight benefit for the server being fixed to the ground when the racquet impacts the ball. At impact there is going to be be a reaction on the racquet, and therefore the server, in the opposite direction of the ball. If the server is fixed to the ground then the ground can react this force. If the server is in the air the server's body will have a small momentum change backward equal to the momentum change forward of the ball. When the server's in the air there are no external forces on the server's body other than when the racquet contacts the ball, so momentum of the server/ball system must be conserved.

I believe this is the issue that some folks are really focused on and it's correct as far as it goes.

However the server is not a passive mass. The server is capable of moving in many different ways, even in the air. At impact, if the server is in the air, the server can bend slightly at the waist. Since the server isn't touching the ground the server's center of mass cannot be affected by this motion. The bending at the waist will cause the upper and lower body to come forward and the waist/rear-end to go back. The upper body will also come down a bit and the lower body to come up since they are connected. The motion of the upper body coming forward will tend to add velocity to the racquet and can react the force of the impact of the ball with the racquet. The sever's center of mass must react backward with the overall momentum change, but as long as the racquet is driven forward into the ball, the fact that the server's center of mass has reacted backward doesn't matter. The server kicks a foot forward and it's all good.

And, if the server tried this trick of bending at the waist at impact while standing on the ground I don't think it would work very well. The server's feet are not actually fixed to the ground. The connection to the ground is only through friction, which requires a normal force. If he pulls his feet up, as bending at the waist would tend to do, he will start to un-weight his feet. Un-weighting his feet will reduce is normal force and thereby reduce the maximum frictional force that his feet can react parallel to the ground, but he will be increasing the required frictional force because he's trying to bend at the waist to create more force at the racquet. It doesn't seem like it will work.


Never has someone ever struck a stationary tennis ball and the person or racket then move backwards. The racket/person will slow down slightly, reducing their momentum and the change in momentum is equal to the change in momentum of the ball. The change in momentum of the ball depends solely on the momentum of the racket. We can accelerate the racket faster by using larger muscles in our body (ie a leg drive. Upwards because that pesky nets tends to get in the way so we must throw the ball up first - thus the upward leg drive lifts the player) and by virtue generating a higher momentum on the racket head via a good kinetic chain. The fixing of a person to the ground is not important. In the same way that an aircraft doesn't drag a large chunk of tarmac behind it for the air to "push off of" so the plane moves forwards. I'm a physics teacher so I talk about tennis balls quite a lot during lessons on momentum!


To say that other sports people dont jump this is potentially true, but they do perform a leg drive to generate momentum. Quaterbacks drop back into the pocket and it allows them to use there legs to drive forwards into the pass. In probably all of these 49td passes manning uses his legs to help generate the arm speed.

http://www.youtube.com/watch?v=_oO3yFVR3IU

I would agree with leed here that there is no advantage to jumping as the extra height on impact is not important.

wow never did I think a Brit would be using american football as an example!

Rob

rkelley
10-11-2011, 12:45 PM
Never has someone ever struck a stationary tennis ball and the person or racket then move backwards. The racket/person will slow down slightly, reducing their momentum and the change in momentum is equal to the change in momentum of the ball.

Let's think about this for minute. Are you saying that, from a practical standpoint, a server striking a tennis ball is not going to be moved backwards due to the momentum change? I'd agree with that.

Theoretically however it's totally possible. Let's say I start my racquet moving at a constant velocity toward the ball while I'm still on the ground. Then I jump straight-up into the air so that there's no component of velocity in any direction parallel to the ground. So the body/racquet system has zero momentum in any direction parallel to the ground (remember the racquet is moving at a constant velocity and its motion was started before my feet left the ground). The ball has no momentum relative to the ground as well. So when my racquet hits the ball conservation of momentum requires that the ball/racquet/body system has zero momentum after the impact. The only way that can happen is for my body to move backward, however slightly.


The change in momentum of the ball depends solely on the momentum of the racket.

I don't agree. Once the server is in the air the server and the racquet form a system. External forces acting on that system will effect the entire system, not just one part of it. If the racquet hits the ball, then the server/racquet system will react that force.

Again, from a practical point of view the racquet's momentum is all that really matters at impact. The head of the 12 oz. racquet is moving at around 100 mph while the server's 180 lb. body is basically stationary. But theoretically I don't see one can exclude the server's body from the analysis.

Rob.D
10-11-2011, 12:53 PM
Theoretically however it's totally possible. Let's say I start my racquet moving at a constant velocity toward the ball while I'm still on the ground. Then I jump straight-up into the air so that there's no component of velocity in any direction parallel to the ground. So the body/racquet system has zero momentum in any direction parallel to the ground (remember the racquet is moving at a constant velocity and its motion was started before my feet left the ground). The ball has no momentum relative to the ground as well. So when my racquet hits the ball conservation of momentum requires that the ball/racquet/body system has zero momentum after the impact. The only way that can happen is for my body to move backward, however slightly.

.

When you are in the air the racket must be moving forwards for you to hit a stationary ball, otherwise you cannot hit it. It does not matter when the motion was started. Therefore you have forward momentum. If you held a racket still and let a moving ball hit it it will move backwards. That is the only way I can think of making a ball move backwards after striking a ball.

rkelley
10-11-2011, 12:53 PM
Thank you for the effort, rkelley, but unfortunately you didn’t convince me.
Can you just explain why in most sports, athletes have never jumped before stroke or throw?:)

I'm sorry Toly, but that's too broad of a question to address. Every sport is different.

I could add that in tennis another part of this equation is the need to put spin on the ball. If players used an Eastern forehand grip to serve it might make more sense to keep your feet on the ground to generate maximum velocity. However it wouldn't matter because you'd never land a ball in. Part of the reason for using a continental grip is that even for first serves you need to get some amount of topspin on the ball or it's near impossible to land the serve. Once you're using a continental grip the serve motion that Federer (and every one else) uses is the best way to maximize power.

As LeeD has pointed out, you also have to serve over your head, the higher the better. I may be able to hit the ball harder by dropping it around my ankles, staying in contact with the ground, and allowing gravity to help me accelerate my racquet, but clearly I'll never get that serve in.

I think we're back to agreeing to disagree.

rkelley
10-11-2011, 01:08 PM
When you are in the air the racket must be moving forwards for you to hit a stationary ball, otherwise you cannot hit it. It does not matter when the motion was started. Therefore you have forward momentum. If you held a racket still and let a moving ball hit it it will move backwards. That is the only way I can think of making a ball move backwards after striking a ball.

It does matter when the motion started. If I start the motion of the racquet before I jump then the ground reacts the force necessary to accelerate the racquet from 0 to its final velocity. After I jump (straight up) the momentum of the center of mass of the racquet and body must be zero even though the racquet is moving forward. If, however, I start the motion of the racquet after I jump, or accelerate the racquet after I jump, then the only way to react the force used to accelerate the racquet is from my body. Once my body and the racquet are in the air the center of mass of that system will move like any particle with the same initial velocity.

Also, technically, my racquet does not need to be moving forward to hit the stationary ball. The racquet/server system can be moving forward. If my body is moving forward but the racquet is stationary relative to my body my racquet will still hit the ball and the ball will still move forward.

I'm not trying to be a jerk here. But I do think it's important to separate the theoretical truths from the practical realities. The practical realities, which I deal with as an engineer, must be subsets of the broader theoretical reality.

Swissv2
10-11-2011, 01:18 PM
You guys.....geez....



Do an experiment. Get a radar gun and try to serve faster with your feet planted on the ground rather than "naturally" rising up to meet the ball. Have a partner force you not to lift off while serving.

See what the difference is. There is your answer.

Rob.D
10-11-2011, 01:26 PM
When you say centre of mass what are you referring to? The centre of mass is the point where all of the mass would be considered to be at if we were to simplify the system to a singular point. How can that be zero?

Unless we are talking about two different things using different words and getting our lines crossed?

And i know your not trying to be a jerk and your not coming across like that so no problems, Its an interesting discussion!

bhupaes
10-11-2011, 01:47 PM
I agree with LeeD - the upward body/leg thrust is because the contact point is high, and the racquet has to start from way below. The only way to build up racquet head speed is to swing the racquet upwards towards the contact point. If there were some way to start the racquet at contact level, or close to it, we may have had a totally different serve motion, and there may have been no need to thrust upwards.

Once racquet head speed is built up, the racquet head is redirected appropriately using complex movements, including pronation. But for the main part, the fact that the arm is attached to the body and is therefore constrained to a rotational path ensures that redirection will happen, IMO.

LeeD
10-11-2011, 02:24 PM
Did anybody ever say the serve is faster if we jump?
I suspect the serve speed is very little difference, but jumping allows a higher contact point which allows more serves to go IN, so you can swing faster more often, to hit a faster ball more often, because you raise your CONTACT POINT when you jump.
End of story.

bhupaes
10-11-2011, 03:08 PM
Did anybody ever say the serve is faster if we jump?
I suspect the serve speed is very little difference, but jumping allows a higher contact point which allows more serves to go IN, so you can swing faster more often, to hit a faster ball more often, because you raise your CONTACT POINT when you jump.
End of story.

I agree that for a higher contact point, the "jump" will be higher - it has to be, how else can contact happen? But the server should should not jump deliberately like a high jumper, since it happens as a side effect of the overall motion - IMO.

You bring up a very interesting point, though. If a player who does not jump while serving is asked to move his contact point higher - without mentioning jumping - will he start leaving the ground naturally? Hmm...

vincent_tennis
10-11-2011, 03:45 PM
Stop confusing people with saying "don't jump," this has been beaten to death. Saying "exploding off your legs" is essentially saying to spring/ aka JUMP. Yes, your leg drive starts the kinetic chain, start researching from there. Yes, you consciously do it or else you wouldn't have a good looking service motion. No, your 12 oz racket and whip of your arm didn't magically propel your whole body into the air.

Bottom line: bend your legs to "spring" into the ball, don't serve like a badminton player.

http://www.youtube.com/watch?v=Wkah8U1GQ_k

you dont jump. lift off the ground is the result of the vertical component of the ke chain...

mistapooh
10-11-2011, 03:45 PM
Did anybody ever say the serve is faster if we jump?
I suspect the serve speed is very little difference, but jumping allows a higher contact point which allows more serves to go IN, so you can swing faster more often, to hit a faster ball more often, because you raise your CONTACT POINT when you jump.
End of story.

What the, I don't even. You suspect serve speed is different? I'm out.

mistapooh
10-11-2011, 03:46 PM
you dont jump. lift off the ground is the result of the vertical component of the ke chain...

Did I not say spring? Did you read the first half of the post or watch the vid? Technically the start of the kinetic chain is YOU JUMPING. You are not lifting off the ground simply because you willed your serving arm to. I'm not saying it's a volleyball serve where the springing motion is independent of the arm whip. Anyone who plays a solid 4.5+, this shouldn't even be up for discussion.

rkelley
10-11-2011, 06:24 PM
When you say centre of mass what are you referring to? The centre of mass is the point where all of the mass would be considered to be at if we were to simplify the system to a singular point. How can that be zero?

Unless we are talking about two different things using different words and getting our lines crossed?

And i know your not trying to be a jerk and your not coming across like that so no problems, Its an interesting discussion!

Sorry. That sentence was supposed to be "After I jump (straight up) the momentum of the center of mass of the racquet and body must be zero . . . "

I agree it is an interesting discussion. Thanks.

rkelley
10-11-2011, 06:28 PM
Did anybody ever say the serve is faster if we jump?
I suspect the serve speed is very little difference, but jumping allows a higher contact point which allows more serves to go IN, so you can swing faster more often, to hit a faster ball more often, because you raise your CONTACT POINT when you jump.
End of story.

I did. The leg thurst, jump, GFR, [insert your name here] increases serve speed. It's not night and day, but I'd guess it's around 10-15%. But you're correct too about needing to get the contact point high to improve serve percentage. Using a continental grip also affects this.

Manus Domini
10-11-2011, 07:38 PM
I do not ask why in some sports athletes jump. My question is: Why in most sports, athletes have never jumped before stroke or throw?
If jump can increase power, they must jump.:)

I would like to point out that once upon a time, pros would hit 140 with woodies, without ever leaving the ground...

toly
10-11-2011, 07:43 PM
I would like to point out that once upon a time, pros would hit 140 with woodies, without ever leaving the ground...

Thanks. This is very good observation.

LeeD
10-12-2011, 11:46 AM
I can certainly be wrong here, but as usual, I doubt it.
PanchoGonzales was reknown for having the fastest serves up to the early '60's. He did not jump, as the rules did not allow jumping. He was 6'4" tall with long arms.
His service speeds were reputed to be in the high 120's, lowest 130's.
The more modern big servers are better trained athletes (trained for serving anyways), and ColinDibley certainly had the fastest serves into the 140's with jumping.
If you don't jump, you don't get a high enough contact point to get a decent percentage of serves IN, so you start to automatically compensate by adding SPIN to your first fast serves.

10smonkey
10-12-2011, 11:54 AM
I would like to point out that once upon a time, pros would hit 140 with woodies, without ever leaving the ground...

I would like to point out that radar guns were not all that accurate back then

LeeD
10-12-2011, 02:11 PM
While I certainly agree that radar guns still ARE NOT accurate to any degree worth comparisons, the best speeds from the late '70's do match up quite well with the current service speeds.
ColinDibley was the fastest, at 149 at the GoldenGateway timing event. His serve is so blindingly faster than StanSmiths (timeed on 3 at just 125), any of the WilsonTeam (around that to lowest 130's), JohanKriek, who could bust a ball, RussellSimpson, who had almost an unreturnable serve if he got it in, that it be hard pressed to argue Colin's actual service speeds.
Remember, the average PRO only hit in the higher 120's/mid 130's. You KNOW someone like DickStockton or RoscoeTanner could hit over 130.
Colin's and Victor Amaya's serves were times well over 140! Victor is a giant at 6'6" and 200+ lbs. They had BY FAR, bigger serves than any of the other touring pros.

Manus Domini
10-12-2011, 06:44 PM
I would like to point out that radar guns were not all that accurate back then

Yet the difference in speed between a woodie serve and a graphite serve is very slight, so I'm not so sure how off the radar guns were.

@LeeD, I'm sure you've heard of Bill Tilden's serve?

LeeD
10-12-2011, 07:45 PM
I've said it many times..... THERE IS LITTLE difference between the serves of a stiff old heavy wood racket or a modern even stiffer composite racket.
Old racket has a higher sweetspot, longer leverage arm.
Old racket is much smaller, and possibly more aerodynamic.
Old racket is heavy, some say it's good for serving, some say not.
For someone like me, the difference is barely 5 mph between a stock, soft WilsonProStaff with BlueStar at 60 lbs compared to a super stiff and aerodynamic aluminum YonexOPSGreen with the same stings at slightly lower tension.
If someone can serve, they can serve with almost any racket.
If they can't, giving them Dr.Ivo's racket does them no good whatsoever.
OK, I could never serve fast with TAD's.

Swissv2
10-12-2011, 10:48 PM
Yet the difference in speed between a woodie serve and a graphite serve is very slight, so I'm not so sure how off the radar guns were.

@LeeD, I'm sure you've heard of Bill Tilden's serve?

Wait...are you suggesting that Bill served at 140mph with this serve action?
http://www.youtube.com/watch?v=izEbU5u5J-I

LeeD
10-13-2011, 09:19 AM
Bill probably served at a real 100.
Pancho could reach 125, but rarely in play. Mostly in exhibitions.
I'd say the first real fast server was JohnNewcombe/StanSmith in the early '70's, after they allowed jumping.
Since I started tennis in '74, I'm no historian.

Manus Domini
10-13-2011, 03:37 PM
Wait...are you suggesting that Bill served at 140mph with this serve action?
http://www.youtube.com/watch?v=izEbU5u5J-I

That seems to be a second serve...