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At the 2005 Competition Training Center Workshop (CTC) held in January 2005, USTA Sport Science Committee members Ben Kibler, MD, Howard Brody, PhD, and Duane Knudson, PhD gave brief presentations on "Technique, Technology and Tennis Injuries." This is the topic of a white paper these three committee members worked on outlining the key point coaches and players should know about injuries and technique.
Following the presentations they held a question and answer period for the CTC coaches. The responses to some of the questions that were asked are included below.
Additional information on the panelists:
- W. Ben Kibler, MD - Medical Director for Lexington Clinic Sports Medicine Center in Lexington, KY.
- Howard Brody, PhD - Emeritus professor of physics at the University of Pennsylvania.
- Duane Knudson, PhD - Associate Professor, Department of Physical Education and Exercise Science, California State University, Chico.
Q: Does stretching prevent injury? Particularly in the wrist - does flexibility in the forearm have anything to do with wrist injury?
Dr. Ben Kibler: Inflexibility by itself is not a predictor of injury. However, what it does, it creates abnormal mechanical motions or inefficient mechanical motions. Then if you do something wrong, or a lot, you can get into trouble. The wrist is a perfect example. Where is the wrist supposed to be in most of your strokes during tennis? Within 30 degrees either way from a neutral position. Therefore flexibility does not play a huge role - unless you are so tight you do not even have those 30 degrees of motion. However, if you get out to 60 degrees or more (of wrist flexion or extension), flexibility will play a role, putting added stress on the joint. Should you do stretching? Yes. Will stretching act as the primary mechanism for injury prevention? No. You have to make sure you are not behind on your strokes.
Dr. Duane Knudson: What we would like to see is a controlled study on this topic, as it pertains to the wrist. We would like to look at some players with flexible wrists and some with inflexible wrists and then track their injury patterns. Unfortunately we do not have that information and my response would be purely my anecdotal opinion. I do believe that if you get to the extremes of the ranges of motion in all your strokes (and you do not have adequate flexibility), and you keep doing it, you are begging for an overuse injury in that part of the body.
One of the sports we do have data on related to injuries and flexibility is running. The data shows that those runners who have the lowest injury rates are those that have "normal" flexibility, or they are in the middle of the range of motion. The runners who are very flexible or very inflexible have the highest injury rates. I tell my students that athletes should strive to maintain normal flexibility by stretching after your activity (tennis play). If a player is very flexible then they should only engage in minimal stretching. If they are super tight, they should stretch like crazy after they play to try to get to that "normal" range of motion.
Q: A lot of times you see players playing up in age group (e.g. a 12 year old playing in 14s). Because of the way the power and speed of the game changes as players get older, does a player who does "play up" put him or herself at a greater risk for injury?
Dr. Ben Kibler: In general I would say "Yes." And the reason I say "yes" is because it is not the power you generate with your strokes but the power you have to accept coming from the other player. I think that is one of the major issues - the power, the load, coming at you. The reason for that is you get behind on your strokes. You get behind on your forehand and your backhand. You're cocking too much. You try to do too much with your arms and don't involve your legs. The other player gets some muscle behind the shot and all you are relying on is technique - because you don't have as much muscle. When you are dealing with players who are 16-18 that may not be as large an issue, but at 12 and 14 you really have to consider it. One of the things we might think about is having players start playing up once they reach puberty. There is a point at which the tradeoff of playing against more experienced players comes at an increased load a player has to face as well as an increased risk of injury.
Dr. Howard Brody: A 12 year old will base the speed of his/her swing on the speed of the ball coming in from other 12 year olds. Moving up to 14s, if the ball is coming in faster, and that 12 year old still swings with the same speed on the racket there is going to be a problem. The 12 year old moving up should not try to hit the ball as hard as he or she did playing other 12 year olds. The 14 year old hits the ball harder. The power, the speed you get off the racket, depends not only on the racket head speed but also on the speed of the ball coming in from the player. So, if you're playing against someone who hits the ball hard, you do not have to match the other player's racket head speed to get good ball speed. And yet, there is a certain macho about trying to do this, and that macho can lead you into trouble. If you are going to play up, do not try to hit the ball as hard as they did against their own age group.
Q: If someone uses a heavier racket is he/ she more susceptible to injury, or vice versa, is a player more likely to be injured playing with a lighter racket.
Dr. Howard Brody: The speed that you get off your racket depends on the racket head speed - linearly; that means if go up 10% in speed (racket head velocity) the ball will leave the racket 10% faster. The ball speed as it leaves the racket depends weakly on the weight of the racket -if you go to a racket that is 10% heavier, the ball speed increases only a very small percentage. If you go to a lighter racket can you swing it faster? Yes, therefore you should get more power. But how much faster? There is no good data correlating racket head speed with racket head properties. If you are a typical player hitting ground strokes, the racket weight typically doesn't change your racket head speed. Very few players swing as hard as they can on ground strokes. It is only when you swing as hard as you can that the racket weight influences how fast the racket goes. On the serve it does, because then you are swinging as hard as you can. But on ground strokes, if you go to a racket that is a little heavier or lighter your swing speed is going to be the same because it is a controlled swing. Therefore, if you go to a slightly heavier racket you will get a bit more 'bang' from the swing. It will be more effort on your part. Which way should you go? The top pros today will take an ordinary racket and weight it. A slight person should take a very light racket.
What happens at contact? A heavier racket will recoil less. A lighter racket will recoil more. More recoil could produce injury. Has it? As far as I know, all the data on racket properties versus injury is anecdotal. I don't know of any study where someone has correlated racket properties with injury.
Dr. Ben Kibler: To quote this white paper on injury and technique. "The racket itself should not be thought of as the most important factor in tennis performance or injury risk. However, if injuries do occur, then part of the evaluation of the cause should focus on the type of racket." In other words, what racket you play with is less important than what develops the racket head speed. It's not the light weight or the heavy weight; it's what you do with your trunk and your body that makes the difference.
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