Beware of Pronation!

One of the big breakthroughs in tennis teaching years about 40 years ago was the discovery of pronation, the outward turn of the forearm, wrist and palm at the end of the service motion that happened so quickly, most observers could not see it. For many years after (and, unfortunately, still today), tennis teachers told their students to “snap your wrist,” which was misconstrued to mean the snapping down and inward of the hand instead of the upward and outward turn. Today, many teachers now say “high-five” the ball.

The discovery and teaching of pronation and the release (not generation) of power it contributes to the serve because of its place at the end of the kinetic chain has not been all positive, however, according to noted biomechanist, Dr. Jack Groppel. Dr. Groppel believes that an over-emphasis on pronation by teachers and coaches who are stressing this part of the kinetic chain out of proportion to its importance is leading to a dramatic number of shoulder and arm problems, and research bears his theory out.

Dr. Bruce Elliot of the University of Western Australia is highly-regarded worldwide for his work on tennis biomechanics and has been a pioneer in the effort to determine what each link in the kinetic chain contributes to overall power.

According to a biomechanical study by Dr. Elliot and his associates on upper limb segments only, forearm pronation contributed only 5.2% of overall speed on a serve! In essence, there is little or no wrist movement on the serve, forearm pronation causes the hand to turn outward, which means all the hand can do is flex at the finish of the serve.

The study found that the majority of racquet head speed on the serve is generated by internal shoulder rotation (approximately 54%) with hand flexion (the outward turn of the hand after forearm pronation, erroneously referred to as the “wrist snap”) contributing 31%.

Dr. Groppel feels this is a major piece of news for tennis teachers because having students emphasize the throwing motion (pronation) instead of internal shoulder rotation leads to debilitating shoulder injuries caused by repetitive stress.

“By teaching the throwing motion first, you’re getting energy to follow back up to the shoulder, which is backward,” says Dr. Groppel. “Having students emphasize internal shoulder rotation which then generates power down the arm to the hand causes less muscle stress.”

Dr. Groppel agrees that pronation is the natural and necessary finish of the service motion, but is convinced that the inordinate amount of rotator cuff and other related shoulder injuries he has seen among junior tennis players is the direct result of tennis coaches over-emphasizing pronation in their teaching and feels the teaching profession needs to come up with safer ways to teach the serve.

“Certainly you want them to pronate because that’s the path of motion and the movement you want your hand and forearm to follow,” says Dr. Groppel. “Even on a slice, you pronate. But what’s happening now is that because they are trying to get increased spin production, coaches are teaching excessive pronation. Juniors’ bodies aren’t strong enough to control the acceleration when they try to hit more spin,” he says. “When they try to get more rotation on the ball with exaggerated pronation instead of just brushing the ball and letting pronation happen naturally, they forcefully create muscular effort to cause the hand to turn out.”

The wrist snap is so misunderstood, one of the game’s leading coaches published an article in Tennis magazine years ago stating that the deep knee bend and upward jump during a serve weren’t necessary to create significant topspin! He pointed out the fact that he could teach wheelchair players to serve more than 100 mph, so the legs weren’t that necessary. However, a person in a wheel chair pushes off his or her chair, which pushes against the ground, serving a similar function to the legs.

Even the most perfect motion is too stressful for the human body, points out Dr. Groppel. A rotator cuff is basically four very thin, ribbon-like muscles. These four crepe-paper like muscles are what stops an arm traveling 100+ miles an hour, over and over again during a baseball or football game or tennis match. The human body is not a perfect machine capable of going from maximum velocity to zero instantaneously over and over. Even with good conditioning and weight training to strengthen these muscles, the serve can cause tremendous stress in even adults bodies.

“Look to see if the junior is pronating. If not, introduce more or different techniques to get him to pronate, but don’t explain pronation,” warns Dr. Groppel. “If the kid’s consciously trying to pronate, trying to turn the racquet outward, then you better change that quickly. Have him keep the arm very loose and brush the ball with the racquet in the direction that you want. That’s it. End of story,” he says.

Dr. Groppel would not teach even a beginner the pronation movement unless the person did not know how to throw. “If they know how to throw, pronation’s going to occur naturally. If they don’t know how to throw, then they’ve got to learn how. So I would start with a beginner throwing, and teaching that movement because pronation occurs naturally as a throwing pattern matures. In all the years I have been teaching, I have never, ever taught pronation.”

Dr. Groppel and other biomechanists have studied the kinetic chain in tennis strokes and understand that each link of the chain contributes to the next link. “I’ve found that if you can use the larger body parts, you can get a very high arm speed without using so much muscular effort. Yes, I can hit a ball very hard without using my legs, but by doing that, I create so much muscular effort in the upper limbs that I’m going to injure the small parts of the arm over time.”

“I find that you can teach spin by simply talking about what the racquet face must do before pronation occurs,” says Dr. Groppel. “By the time the hand turns outward, the ball is gone anyway. Pronation should be something that happens naturally, not something that you make happen. Pronation contributes nothing to the spin of the ball, it just allows you to finish with less stress.

“I believe we need to teach spin by brushing the back of the ball. For example, if you’re going to teach slice to a right-hander, you talk about hitting from 8 to 2, or 9 to 3 on the face of a clock. For more topspin, it’s more like 7 to 1, which is also like the old American twist. What scares me about 6 to 12 is that the only way to do it is to arch your back, and you’re really going to hurt your back.

“I like the way the Standard Method addresses spin by using that concept of ‘bypass the ball.’ If the student has the racquet on edge, as demonstrated in a Standard Method lesson, for example, the student makes contact and pronation is going to occur naturally. You don’t need to talk about rotating the hand so much. Talk about rotation of the racquet, where they’re not going to create muscular force — the racquet is going to come up on edge, and just make sure the palm and the racquet face is facing into the court when you make contact. Everything else occurs naturally.

“The danger comes in when pros get a junior who is ready to go to an aggressive spin second serve. Then the coach says, ‘To get more spin, pronate.'” Dr. Groppel recommends teaching spin without power, first. “With a lot of these things we’re talking about, pronation is the descriptive word. Pronation occurs, but it’s much more an internal rotation of the shoulder. It goes all the way back to the throwing motion.”

“Teaching sidespin on a serve is like teaching topspin on a groundstroke, there’s only one way. How do you teach topspin groundstrokes today? No one teaches topspin by rolling the racquet over at the end of the swing,” points out Dr. Groppel. “Then why teach pronation if, by the time all the pronation occurs and you get the hand turning outward, the ball is gone? That’s the same as teaching rolling over the ball after you hit to hit a topspin groundstroke.”

While there is disagreement among biomechanists regarding just how much power each link in the kinetic chain contributes, they clearly agree that over-emphasizing one link in the chain, as is commonly done with pronation, can lead to serious injuries in our students.

An approach to teaching the serve which helps your student understand the concept of the kinetic chain will increase their ability to develop a safe, effective serve for many years.

What is Power?

What is “power”? When we refer to power, we’re actually referring to ball speed. Another word for speed is Force, so using the formula, Force = Mass X Acceleration, the more mass (body) you put into a stroke, the more acceleration you will create and velocity and ball speed you will achieve. This is why the semi-open or open stance on the forehand and two-handed backhand, as well as the deep knee bend and extreme trunk rotation and players’ taller and more muscular frames have sped up the game – – it’s not the new rackets.

While visiting Hilton Head Island during USPTR Week 1996 and working with Dennis Van der Meer on their upcoming tennis video, Richard Schoenborn discussed his thoughts on the new Elliot study and his research on power generation during the kinetic chain. Surprisingly, Dr. Elliot’s research indicates that the deep knee bend and push off during the serve contributes only 10% to racket head speed on a serve.

According to Schoenborn, however, a tennis serve requires approximately 4,000 watts of energy, of which only 300-600 watts can be generated by the arm depending on the size of the athlete. Therefore, the majority of velocity on the serve must be generated where the body has the most mass — from the knees to the trunk.

According to Dr. Elliot, the knee bend serves to drive the racquet down behind the back, which increases the distance to build racquet speed and stretching the muscles that drive the racquet to the ball. This creates elastic energy. Dr. Elliot concurs that the trunk plays a major role in serve velocity, pointing out the shoulder is considered part of the upper body, not the arm. The reason a body part with such little mass, like the hand, contributes so much to racquet head speed is the velocity is more generated by angular rotation (such as quick hand flexion) and length of lever (a tennis racquet) than by mass.