Katrina Adams in 15-30

[10splayer]

Yeah, Doug's great, so are you and stotty, and many others. I too am enjoying this forum.

[DougEng]

Thanks for the comprehensive follow up to my post. I haven't read the Bruce Elliot and Duane Knudson articles yet, but will avidly.

Speaking from personal experience, I feel the bulk of my power comes from the upper arm and shoulder...virtually all of it. There is a link to me serving somewhere in the forum but I couldn't find it. Nevertheless, as you mentioned, all servers are different. I use very little leg drive so it would make sense the feeling of power comes mostly from the upper arm and shoulder.

Pro serves of course are a whole lot different. Every part of the chain is being used to generate power, and it's interesting to see how and where the power is coming from. The wrist is the biggest mystery in the serve, for me...and the only way to judge it is from personal experience...but it's so hard to quantify it even in your own serve. The wrist feels like it is doing very little when I serve...except perhaps in a kick serve, where it feels it's doing a little more. But I only serve at 85-90mph and have no conception of what it feels like to deliver one at 130mph...let alone the 150mph barrier which some pro's can cross.

Pro's don't always get all parts of the motion right either, though. Below is a clip of Ryan Sweeting, which I took a few years ago at Wimbledon - where he was routed by Nadal. His serve is a mess...the elbow is so low and he struggles to compensate for this error during the second part of the action. It's scary how he could have passed through so many coaches' hands and not have such a basic fault rectified.

http://www.youtube.com/watch?v=UsT2mqnQrQ0

This is a great thread. I've learned a good deal...things I didn't know. Interesting how the input from the wrist may be higher or lower depending on the server....with pro servers, one would think it would be roughly the same.

I just wonder how such quantitive measurements are made? How do biomechanists come up with these percentages? It would seem impossible without sophisticated devices of some kind?

Thanks for bringing up this unusual video!

That Sweeting serve is a bit unusual. The elbow position is not as important as some pros suggest. It depends when it occurs and how quickly a player can recover. Nonetheless it isn't desirable and in this case it makes Sweeting's serve more difficult. The elbow actually does achieve a reasonably high position later in the stroke. However, Ryan is slow to get into the late cocking stage (racquet is vertical) since he is very late getting the elbow up. The rest of his body is slightly ahead of the optimal cocking. Therefore he opens his hips up a bit early when his racquet finally comes up to contact. I imagine he might have hit a bit flatter and may have had a few extra double faults in this match. This is just a quick analysis based on this motion. To make a more accurate judgment, one would need to see a couple different views, first and second serve and see some actual statistics from the match. But quite interesting!

I'm not sure about Elliott's subjects but I wouldn't be surprised if it was perhaps with 5-20 subjects with force plates and video analysis with markers. I might have time to find it sometime.

Best,
Doug

[DougEng]

I am constantly amazed and impressed by the depth and breathe of knowledge that Doug Eng brings to the forum. I consider myself pretty good and try to educate myself about what is being learned about the game, but I always come away feeling woefully inadequate when I see the information that Doug puts up here. I'm so glad that he is participating a little more regularly now. I try to go through some of these scientific presentations, but it's really not that easy. I really appreciate some of the simplifications and clarifications that Doug brings to us here. I hope you keep it up, Doug.

I will try to get through these journal articles and see what I can cram into my thick skull (seems to be awful leaky these days), but I do have a few questions that some of these power contribution breakdowns raise for me. I may not be able to handle a bigger boat, but I could certainly use a longer, lighter paddle to help me navigate this boat along this blankety-blank creek of knowledge!

First of all, about the leg drive.
There is no question that the legs make a significant contribution to the power of the serve. But I would argue the 10 to 20% of power that comes from leg thrust and trunk rotation comes primarily from trunk rotation. I used to be able to serve pretty well standing on one leg (as a demonstration); but while I stayed balanced and my knees bent hardly at all, I would never have thought of restricting the rotation of my hips or of my shoulders from sideways to facing the net as I did that. I see a tremendous problem with kids trying to leave the ground or at least use as much upward leg thrust as possible when they have not yet truly mastered trunk rotation leading them up to a solid contact with the ball.

In fact I'm one of those coaches who tries to get my students to serve with no step and simple balance

http://www.tennisplayer.net/bulletin/showthread.php?p=20687#post20687

before I let them move on to leaving the ground. I may just be too wedded to the old school serve and volley principles, but even though that rear foot kicks back up into the air, its first contact with the ground should be well in front of the other foot. This is true even for a committed groundstoker like Agassi. My first movement in the direction of the kickback is a simple rotation on the rear toe so the right knee (for righties) lets the right hip get forward.

Sure baseball is limited by the rule that the toe has to stay on the "rubber" until the pitcher releases the ball, but quarterbacks have no such limitation. And we don't see them trying to leave the ground to get more power into their throws. Better yet, take any of your good players and stand next to them and feed them some high lobs for bounce overheads a few feet behind the service line. I have yet to find a player who hits the ball better in that situation by leaving the ground. On the contrary, I try to use the feeling they develop hitting that ball to get the sense of using their legs for power in their serve with stability and balance that leads to consistency and accuracy as well as power. You can use the ground to drive the trunk rotation that provides the real leg power to that overhead.

I'm getting carried away as usual, but my point is there needs to be a better understanding that the "10 to 20%" from leg drive and trunk rotation is primarily trunk rotation (I have no scientific study or biomechanics data to corroborate what I am saying here so feel free to prove me wrong) and most of the kids I see are sacrificing 10 to 20% of their overall power because of the compromise to their kinetic efficiency created by overemphasizing knee bend before they have true command of the basic upward strike. Oh yeah, they might be getting 3-5% more power because of their excellent knee bend; on top of that they can't get the ball in the box because the motion is too complicated for them to repeat consistently. NO, I don't think 60 to 65% is a good first serve percentage; especially for anyone over 6' 2" tall, much less 6' 4".

Second, the idea about it being easier to go faster at 50mph than 10mph. Recognize the difference between static and sliding friction. It's much easier to keep something moving once you get it started moving, but from a physics point of view, it is not going to be easier to accelerate something from 40 to 50 mph than it is to accelerate it from 10 to 20 mph. Percentage wise, it may be a smaller jump (25% vs 100%), but the amount of work is actually more. In terms of the forces on the racket, perhaps the coefficient of sliding friction for the racket through the air molecules my be slightly less (I don't know), but I do know that the wind resistance is proportional to the square of the velocity of the racket. That's one reason your gas mileage goes down as you get your velocity goes up. So no, you don't want the racket head to come to a dead stop, but it doesn't make sense to me that it is any easier to accelerate the racket head from 50 to 80 mph than it is to accelerate it from 20 to 50 mph.

Finally, all this emphasis is always on how to generate more power. But at what cost. The stroke has to be produced in a manner that enables consistency and accuracy under sometimes very difficult conditions. Big, thick, heavily muscled bodies might be able to generate a little more power but those players would then have to schlep those muscles with them wherever they went. Physical power has to be balanced and matched by flexibility, speed and endurance. (What a wonderful game!!) In a different way, powerful strokes (or service motions including the toss) have to include the ability to generate tremendous levels of consistency and accuracy. Where does the "flip" or the Type III vs the Type II or Type I forehand backswing fit with regard to that perspective? Could an old timer without much of a flip hold up with his greater consistency against the heavy ball of a modern player with a "flip" and the concomitant increased spin and velocity. I doubt it, but you might get a different answer from some to the NorCal players trying to handle Karsten Popp.

http://www.tennisplayer.net/members/classiclessons/scott_murphy/traditional_forehand/

Looking forward to getting ripped to shreds here. Always good to learn. Maybe it will make it easier for me to accept that the kids don't take everything I say as gospel. I keep thinking if I had only had someone with my knowledge to tell me what to do, it would have been so much easier and I could have been so much better. Probably would have still been too slow, but what fun it would have been to have a reliable forehand, much less a weapon instead of a gross liability. After all, you know the reason Hop named Rod Laver "the rocket". He was the slowest in the team wind sprints! At least that was the story I remember.

don

Hi Don,

Interesting point on Rod Laver. And yes, muscle-bound athletes may struggle at tennis. If you ever taught an American football player tennis, yes...you'll see firsthand!

The static/slidiing friction concept doesn't really apply to tennis, although I implied the analogy of the car. Drag or air resistance isn't really much of a factor in tennis with racquet head speed...but much more with the ball.
With wind resistance, yes, moving a car at 40-50 mph can require more energy. My point was changing impetus where at high speeds, it is often easier to continue since force is already applied. At some point with motor vehicles, wind resistance causes excess consumption of energy (e.g, 75 mph has lower gas mileage than at 45 which has better mileage than going at 15 mph). Just as if you dropped a tennis ball from a skyscraper, the ball would accelerate but at some point, the resistive forces equal gravitational force and hence the ball reaches terminal velocity. Human terminal velocity is about 120 mph. But don't try it unless you have a parachute.

So it is harder reach racquet head speed of 60 mph using only the arm than it is using the legs. Consider it like wind-assisted running. Or if you jumped off a moving car, you gain the car's velocity and your overall speed is higher (and impact with the ground is higher).

Once the elbow extends, pronates and accelerates, the wrist can "jump off" to provide that last bit of extra velocity. But by itself, it won't work.

In addition, I think I might have mentioned elsewhere, flexibility is good for sports but also bad. What really matters is strength within a flexible or superior range of motion. Good athletes have excellent flexibility but strength and highly stable joints at extreme ranges. A child is very flexible but doesn't have strength in hyperextended positions, risking injury. Some very strong athletes may lack flexibility and hence cannot utilize optimally the kinetic chain. And relaxation/tension may limit an efficient kinetic chain.

In the case of Rod Laver:
1) his fast twitch muscles might be more in his arms and upper body, hence he had a powerful serve.
2) he almost definitely had a more efficient kinetic chain than most pros (maximizing physical attributes)
3) his reaction time was superior to many, so his first step was explosive and quick and he was quick to react on volleys. But running over a distance might be less effective.
4) he anticipated and read the ball well

In tennis, the first step with good reaction/anticipation is more important than overall speed. The average distance to the ball during match play is about 8 feet of running. That's not far so it tells you something, what does the player do in this time? Of course, Djokovic vs Nadal or Murray...they don't average 8 feet of running to each shot...probably 50-75% more, the way they play points!

Best,
Doug

[10splayer]

Given the amount of feedback already, I might as well give my take now.
John Yandell didn't want to say too much since it was already stated
and sometimes it's best not to criticize directly. But John's implications
are on the button.

Explicitly, 10splayer hit it on the button. Also, Stotty (licensedcoach) the follow-through on the dominant side is acceptable and is a characteristic of the American Twist serve. The kick and American Twist produce the same spin. Katrina is actually describing upwards racquet path of the American Twist serve. That very vertical drive is then followed by the follow-through on the right (e.g, Fabrice Santoro). The modern kick serve is a different motion, at 2 o'clock and the follow-through tends to be more normal. The American Twist serve is more strenuous on the back since there is often some lumbar back extension (aka back arch). The extension probably maxes out at 10-15˚, which is minor. The modern kick serve doesn't need the same lumbar extension.

The concept of arching the back has been essentially thrown out by biomechanists and the sports medicine community since there is concern about back injury (as with Stefan Edberg had some problems). In the serve, most people use 10-15˚ of lumbar extension but relying on this to produce power has been suggested to lead to injury. It is not a source of power as with, for example, use of legs, hip over hip, internal shoulder rotation, wrist flexion or long axis rotation.

The lumbar region of the back has maximum extension of 25˚ but the serve may be typically 10-15˚. Maximum hip extension is 25-30˚, on the serve, realistically it may be 10-15˚. Together, the total backwards extension might typically be 20˚ (30˚ is exceptional). However, it may be confused solely as back arching. That is, hip extension is often confused with lumbar extension or back arching since it occurs concurrently in the serve loading position.

So if hip/lumber extension is not for power, why do it? American Twist serves require the toss to go behind the left shoulder or front left of the front shoulder. To hit the ball slightly back, extension backwards occurs as the player looks upwards. Since gravity is a force, the upper back is now off balance, which obviously creates a lean back. As the legs initiate the kinetic chain, the legs will straighten out first before translating energy upwards. A delay in the upper body results in greater extension. In a modern kick, the toss does not need to be as far back and hence, lumbar/hip extension can be less. The modern kick is therefore less strenuous on the back than the American twist. Federer is a good example of a proponent of modern kick serve. Without significant extension, he can get significant spin.

Second, Katrina's description of the racquet coming over the ball is incorrect.
She demonstrates the racquet coming around about 90˚ (1/4 circle) of the ball. That motion was often used by coaches in the 50s through 80s but is rarely used today since we know the ball typically stays on the racquet strings in the order of a few milliseconds where the racquet can only travel a few inches and not enough to go around the ball. About 5 years ago, after a lecture/presentation I gave, I heard a fairly well respected coach take the same things I said and misinterpreted it to what Katrina said. So it is possible, even today, with high speed videography and science, people still misunderstand.

Kudos to 10splayer.

Also there was a lively discussion of the "arching of the back" concurrently with the knee bend. Essentially, the body tilts back (with slight hip and lumbar extension) as knee flexion (bend) is typically 90˚. That can tilt the body above the knees maybe 30-40˚ as the lower legs tilt the opposite direction. Add the 20˚ of combined lumbar and hip extension and you get a nice L tilt. From this early cocking (biomechanist term) or loading position (or popularly trophy position), knees begin to straighten out as energy is translated through the hips (to get hip over hip action).

The arching of the back has been misunderstood much like arm extension. Many coaches still teach extension as reaching upwards to the ball. For many beginners, this translates to reaching above the shoulder line. Extension is really produce by shoulder over shoulder (from hip over hip) tilt. If you tilt the shoulders, in extreme examples of powerful serves (e.g, Sampras), the shoulder over shoulder tilt is ca 70˚ which allows the arm to reach up. Club players often only tilt less than 30-40˚ and still try to reach up which creates shoulder impingement. I find this also common among average ranked juniors.
The upper arm basically should only raise 10˚ at maximum above the shoulder line.

Attached are 2 slides from the ITF biomechanics presentation on the serve which can help foster understanding of body position/joint mobility during the serve.
(itftennis.com).

Best,
Doug

This is very important for the layman to understand. IMO. When the body rotates shoulder over shoulder, the backside (hitting shoulder) is driven up, or elevates, so the shoulder/arm can work within it's proper range of motion. There is no need to reach up (with the arm) to find the appropriate contact height.

On the flip side, when the body rotates too "level" the arm must be raised to find the ideal contact height. This is one of the most misguided, misdiagnosed, problems I've seen. Getting the body to rotate on the proper axis will solve many problems. Nice post.