Last summer, I spent lots of time trying to fully understand why things occur in the game of tennis. I spent lots of time taking photographs of the pros on the two tours. I videotaped matches and played parts in slow-motion. I spent lots of time watching myself on my high-speed video camera, which really allows me to see the stroke in a very slow motion manner.

Last month’s column was a direct consequence of my observations using these tools. Well, I don’t want to disappoint you this month. So again, my column will address a part of stroke development and execution that results from my summer’s work.

There are many things that can cause a shot to go errant. First and foremost, the racquet face’s "direction" at the moment of impact is the most common error for those new to the game. You can actually hit down on a ball (from high to low swing) and still hit the ball high, if the racquet face is pointing upward at the moment of contact. Beginners usually need some time working on hitting with a steady, perpendicular to the ground, racquet face. More experienced players do this without thought or effort, if their strokes are well developed.

Second, people will often times over hit the shot. In their quest to be dominant, the player will hit with more pace than she/he can actually handle with control. In junior players, I see lots of this. Most shots, the junior can really hit with pace and keep the ball in the court and away from the net. But, this power is seductive. Often times, the junior will start bashing every shot with reckless abandon. The result is obvious…errant shots.

Third, shots may go errant because one or both, of two things, did not occur correctly: the player’s head was not "frozen" at the moment of impact, and/or the player did not finish the stroke properly.

If you are really focusing on the ball as it travels, it is easy to forget to quiet your head as you make contact with it. Like the game of golf, good tennis requires the head to be still and motionless when the racquet face actually makes contact with the ball. Thus, I refer to this as "freezing" one’s head.

Also, proper stroke finish is essential. I assure you that if you finished each stroke properly with a good follow through, your shots would be far less likely to go errant.

Lastly for the purposes of our discussion, having your body stretched at the moment of impact causes many errant shots. For example, an opponent pulls you wide with a shot. You scramble to get to the ball. You are stretched to the limit when you make a miraculous contact with the ball. Well, if you try to hit a regular or forceful shot from this position, you are certainly going to hit an error. In these "emergency" situations, you must have defensive shots in your arsenal. Lobs and sliced shots off of both wings are the only realistically viable shots when you are stretched this far. Again, juniors will often times try for a big shot in these situations…a recipe for failure!

Somewhat related to this last cause of errant shots is the concept of what I call "centering." Really, tennis is not only a game of skill, athleticism and endurance…it is a game that involves body balance. When the body is even slightly out of balance at the moment of impact, the ball has a much more likely chance of going errant.

These off-balanced situations occur throughout a match. How one handles them is critical. But, before we get to that, we need to understand clearly how often our body is "off center."

Last summer, I spent literally hours viewing and reviewing still and video footage. I discovered that when one looks at even a top 10 pro in slow motion, one will see that there are many times when the pro’s body is ever so slightly out of balance. Most often for pros, this little misbalance is of minor consequence. Their bodies and minds have hit so many balls, that the body/mind combination immediately "adjusts" for the imbalanced hitting situation.

Let me give you a concrete example. In one bit of footage, an unnamed pro was receiving serve. He was given a serve that came straight at him with significant pace. In short, he was "jammed" by the serve. Well, viewing this serve in slow motion, one notices that the pro immediately lifts his body upward, while "blocking" the serve. This upward motion is a natural way in which the body compensates for the lack of balance at the moment of impact. The pro is wise enough to realize that the blocked return is the only viable option.

On clay, it is natural to see players sliding as they make their groundstroke shots. This sliding is very useful, in that, it not only provides a natural way for the player to recover from the shot and get back into proper position for the next shot…it also balances the body at the moment of impact. If you watch carefully at slow motion replays of professionals hitting on clay, you will notice that their bodies are low to the ground as they slide. The knees are naturally bent, and the center of gravity is low.

Now, balls bounce higher on clay. I asked myself the question, "Why would the pros go lower to hit these higher bouncing balls?" After lots of video examination, I discovered my answer.

First, the best clay court players, like Nadal, always use a semi-western or full western forehand grip, and more often than not, are two handed backhand players. Both of these are perfect for hitting high bouncing balls. Stand erect, and use an eastern forehand grip or hit with a one handed backhand, and you are automatically at a disadvantage.

Certainly, one handed backhand players can win on clay. One has only to remember the incredible Tomas Muster! But, the one handed player on clay has to be able to hit the high ball. On slower clay surfaces, this usually means getting under the ball as you hit your one handed backhand. If you watch Federer on clay, he does not always have the ability to get under the oncoming ball, and hit up. This becomes particularly true with his return of serve.

On grass, you will see players, again, keeping their center of gravity low. You will hear their coaches telling them to "stay down" on the shot. Why? Well, grass does not allow for a high bounce, and as it becomes "chewed up" from play, the bounces become very erratic. On almost any shot in the finals of Wimbledon, the players will find that the ball is not taking a true bounce. Thus, the serve/volley player with competence and speed prevails more often than not.

Hard courts usually are very predictable. Granted they can vary in terms of speed and bounce, but once the player is familiar with the specific surface, he/she can determine the ideal ball-contact combination with predictability. It is on these surfaces that the airborne player really thrives.

By airborne, I mean the player who literally is lifted off the ground as she/he hits a groundstroke. Andy Roddick is such a player. The consistency of the surface really allows for this to occur with regularity. By going airborne, the player can hit the ball with greater pace and still expect it to drop within the lines. Why? Well, this upward movement contributes to topspin, which keeps the ball arcing downward as it travels. Using the kind of racquet head speed described in last month’s column, the pros on both tours when competing on hard courts hit incredibly forceful shots.

You will see most professionals going airborne on clay surfaces, as well. However, they are launched upward from a much lower starting point. By this, I mean that their center of gravity is lower as they begin the stroke. Why are their shots less forceful? The clay surface slows down every ball. The "retriever" player with good "wheels" is never out of a clay court match. In fact, the French Open was the only Grand Slam event Michael Chang ever won…as a teenager!!! He ran for everything and was blessed with incredible speed and endurance in his running.

So by now, you are probably asking yourself, "Okay, Ron. What am I to learn from all of this?" Certainly, this is a fair question, to say the least.

First, recognize that your body’s center of gravity as you make your groundstrokes is an incredibly important variable.

Second, try to monitor your practice from the perspective of balance. Learn to "feel" when the right body motions are in place for your strokes. Videotaping your strokes and viewing them in slow motion will show the slight imbalances that occur when you are not hitting "perfectly."

Third, there are two principles of body centering which I believe need to be in place to succeed on a variety of surfaces. First, you need to be able to hit groundstrokes from a low center of gravity. If you literally bent your knees even a little bit on every groundstroke as you took your backswing, you would find fewer errant shots in your game, I assure you. Even slice shots on either wing benefit from these bended knees. The difference is that the racquet motion is high to low…not low to high. Thus, you need to stay low through the slice shot. Lifting up as you hit flat or topspin groundstrokes will benefit your body stability and shot consistency.

Fourth, the natural reaction for the body when presented with a "quick response" in tennis is to lean back and to move upward. Many hours of viewing video at night has taught me that this is true. The upward motion of the body is wonderful and actually helps body stability and shot consistency. The leaning backward is not at all useful.

When you "feel" yourself leaning back, you must, I repeat, must hit with an upward racquet motion. On clay, you will note that some players deliberately will be leaning back as they hit their groundstrokes. I asked myself, why? It actually makes sense. By leaning back, the pros are automatically going to hit the ball with more of an upward swing. This means greater net clearance and greater topspin…the two ingredients that are necessary for success on clay.

If you can, learn to go airborne on your groundstrokes. Initially, this will be awkward…especially if you are an older player. But, even if you can’t go airborne, at least, move your body upward as you make contact with the ball. This upward motion is, in my mind, what is essential in eradicating or minimizing the presence of imbalance in your shots.

Lastly, practice balance!!! Yes, you heard me correctly. You can and should add balance practice to your tennis training regimen. Frankly, I am discovering new ways to practice balance each day.

Start with this exercise. Simply walk the baselines and sidelines of a tennis court. However, in doing this, place one foot in front of another. Each foot should be placed perfectly on the line. Do this slowly, at first. Increase the speed, and it becomes a bit more difficult. I practice this regularly, and I have found that, in being able to increase my speed in this drill while placing my feet perfectly on the lines, I have improved my overall balance.

As a child, we almost all have walked on a raised curb associated with a road. I have found several parking lots where there are these raised concrete curbs. I now practice my balance by walking on these. To increase difficulty, try to walk the curb without looking at your feet. Do this latter variation slowly, at first. The last thing you want to do is to twist and injure an ankle.

At home, I have devised a method of helping me practice my balance. Being a professor, I have loads of books. On my living room floor, I place single and two book piles within a 10 foot by 10 foot square. I literally play "Twister" by moving from book to book pile in a random manner using both feet. The key to safety, here, is making certain to tape the book piles together using a heavy duct tape. You don’t want the books sliding as you move onto them.

Lastly, I have started to do my standing stretches for my legs without putting my hands on any support. This in itself creates an interesting balance problem.

I believe we can all learn to improve our balance. I would be curious to learn your techniques for practicing balance. Certainly, my studies show that balance, and associated corrections, play a critically important role in proper shot execution. Low centers of gravity on the backswing with an upward movement for all groundstrokes ,except sliced shots, will pay huge dividends. If you can learn to go airborne, even better. It is the ultimately effective correction.

Work on your balance as you train and I assure you that you will soon become a tennis overdog!