Rod Laver's lobster-like left forearm is an enduring symbol for the public's perception of tennis as a one-handed sport. Indeed, a player's hitting arm takes on the lions share of responsibility for delivering power, spin and control to the ball, but that belies the importance of the non-hitting (other or off-side) hand. Most non-A players use the non-hitting hand to toss the ball up on the serve then pretty much forget about it, letting it hang at their sides or flop around randomly like a like a bologna sausage. If you watch the pros and focus on their non-hitting hands, you will find that there are complex and stereotypical movements of the off-side limb in every stroke. This observation implies that the non-hitting hand has an essential role to play. Even one-armed tennis players use whatever they have remaining of their absent arm on all of the strokes.

Functions of the non-hitting (Other) hand

• source momentum for the power wave for volleys and short strokes
• start and end the shoulder-over-shoulder (cartwheel) service/ overhead motion
• prevent over-rotation on ground strokes and volleys
• find the proper pose
• ensure sufficient shoulder rotation in the unit turn
• trigger the explosion at the end of the Lag phase

One function you will not find on this list is to maintain balance. You should never use your other arm for balance. It is not required for balance because to execute a stroke one must be in dynamic balance and in dynamic balance the location of your center of gravity and hence the position of your extremities is irrelevant. If you look at Federer's one-handed topspin backhand, it looks like his other arm is being thrown out for balance, but it is otherwise occupied starting, reinforcing the stopping the rotation of his body.

Counter-rotation

When we talk about a "power wave" coming up from the feet and being captured by the hitting arm and transmuted into pace, control and spin we are talking about gross motor movements and raw power. What about fine-tuning the power wave? How does the wave start and how does it stop? What about short strokes like the volley wherein there isn't time to push off from the ground and then wait while a wave of power meanders its way up the body?

There is another way to start the body rotating into a stroke; by counter-rotating with the non-hitting arm and shoulder. In the forehand volley, for example, if you throw the non-hitting hand across the chest the rest of the body will rotate in the opposite direction. If you stop the non-hitting hand suddenly, the hitting hand will decelerate suddenly. Since the non-hitting limb is connected to the hitting arm through the shoulders this all happens very quickly - a few milliseconds. Since the non-hitting hand is not otherwise occupied during the load and explode phases, it can make this contribution to the stroke without any conflicts. Once this role of the non-hitting hand is understood, several heretofore impenetrable mysteries can be dispelled;

• How can one hit a solid, well-placed volley with no swing at all?
• Why do some volleys send the ball into the base of the net or the back fence?
• What is the difference between a well-hit short stroke and an uncontrolled bunt?
• Why do great servers all "follow-through" on the ball toss, reaching for the stars even though the ball leaves the hand at shoulder level?
• Why do pros consistently and sometimes violently throw the non-hitting hand behind them on the one-handed backhand and backhand volleys?
• Why do the pros point at the ball on the overhead?

These queries implicate the off-side hand in starting, stopping, energizing and regulating the rotation of the shoulders during the stroke. In the case of the forehand volley, much of the "power wave" comes from the movement of the off-side limb. In the preparation for the volley you bring the off-side hand 45 degrees out and down from the ready position. You then begin the volley stroke by pulling the off-side limb in and up towards the point of contact which counters the the action of pulling the hitting hand down and across to meet the ball. Since the momentum of these two actions cancel one another, you have suceeded in "manufacturing" momentum that can be applied to the ball by the hitting hand.

Taking Control

The mini-power wave produced by the off-side arm helps create the acceleration that loads the muscles of the forearm storing directional control and spin forces. Without the power wave, the forces don't get loaded, and the racket is nothing but a wall off of which the ball will bounce in any way it pleases, often towards the base of the net. When the off-side arm stops, the wave dissipates, and the acceleration of the hitting arm stops, releasing the stored forces into the ball through the good offices of impulse. In a short stroke like the volley, there need be no actual movement of the racket during the stroke, and there is often minimal residual inertia, so there is little to no follow through. We call that a "crisp" volley, with all the appropriate admiration and respect it deserves since those volleys are the firmest and best placed. In a crisp volley, the backswing proper, or lock phase, results from simply reaching the racket out towards the point of contact from the ready position, so there is nothing visible that is comparable to the backswing of a groundstroke. The act of opening up the racket face to the ball is all the lock that is needed to prepare the racket-wrist-forearm unit for the loading the stretch-shortening force. The result is a virtual swing - an invisible swing - that delivers excellent directional control and spin to the ball without adding any unnecessary pace and takes only a handful of milliseconds to execute. Just call it magic. Of course, if you want to give the ball a ride and happen to have a little extra time (a nice floaty shoulder high volley for example) you can pull the racket up and lean it back a little more in the lock phase. This action creates room for a super-short lag phase to add some racket head speed - as long as you remember never to drive through the volley and to pull, not push, into the ball.

Finding the Pose

An essential tool in any sport that depends on complex movement is the pose. The pose is the attitude of your entire body just before executing a stroke. It occurs after the unit turn and just before the backswing proper. Its main functions are twofold:

1. Getting the shoulder, arm, wrist, and racket into proper alignment for entry into the backswing proper (or lock)
2. Queuing up the stroke in preparation for "playback" by the Thalamus

A proper pose is one that is easy to remember and "different" enough from any normal attitude of the body that it tickles the site in your brain where you store the particulars of the desired stroke. Since the hitting arm needs to be in a position such that the lock phase can properly "lock in" stretch shortening during the backswing proper it is limited in its freedom to be able to evoke stroke memory. The other hand and arm aren't very busy at this point, and they can occupy themselves with the critical task of helping the Thalamus find the right tape to play. At the same time, the other hand can often guide and hold the racket in the proper alignment, height and facing to ensure productive entry into the lock phase. The participation of the non-hitting hand can mean the difference between a shot with sufficient spin to keep it in the court and one that flies over the baseline. Racket preparation in the pose determines the orientation of the racket face on contact, the amount of racket head speed, even the timing of the entire stroke. In a very real way the attitude of the racket in the pose determines the outcome of the shot, and for that reason alone the participation of the non-hitting hand in volleys and groundstrokes is a prerequisite for adequate consistency.

The Unit Turn

The first "move" into a groundstroke or volley is the unit turn. It is the sloppy, often violent transition from the "ready state" of being prepared for either a forehand, backhand or overhead to a state wherein one is ready to begin the stroke. It can be the most time-consuming part of the stroke, hence the sloppy and violent part. Luckily it is pretty simple and easy to execute. One does not need to be in dynamic balance when it starts but should be in dynamic balance when it finishes. You can do it while running down a wide ball. Although simple, it is one of the moves that players who are talent challenged very often mess up. The most common and most egregious fault is to throw the racket back but not change the orientation of the shoulders and hips. This incomplete preparation is bad on many levels. Firstly it does nothing to get your feet moving. Indeed it is conceived by the lazy part of your brain as a way to hit the ball without the necessity of tiresome footwork or balance. Second, it opens up the hitting shoulder in a way that is unrecoverable. When the shoulder and hitting arm is parallel to a line drawn between the shoulders, it is weak. When it is at 45 degrees or more in front of that line it is strong. To "resist" the powerful acceleration that results from the rotation of the hips and torso the shoulder needs to be strong. Finally, if the shoulders and hips don't "wind up" before the stroke, they will have nowhere to go when the legs drive around and forward.

Failure to properly execute the unit turn is due to lazy feet. The feet have to move to get from the ready position to the unit turned position because moving feet lead to dynamic balance. If you are not in dynamic balance by the time you begin the backswing proper, then that move itself will throw you off balance. Now here it comes: If you have the other hand on the throat of the racket during the unit turn, the shoulders have to follow the racket back, the torso has to follow the shoulders back, and the hips, legs, and feet have to follow the torso back around into the perfect, coiled position for the stroke. As an added bonus the steps your feet need to take to assume this new position get you into dynamic balance. All from just not letting go of the racket with your non-hitting hand during the unit turn.

Over-rotation

If you don't like hitting the ball over the baseline, don't over-rotate. Over-rotating occurs when your hips and shoulders continue to rotate or even accelerate through the moment of contact with the ball which seems like a natural thing to do; keep pouring on the power every millisecond you can! Drive that ball into the court! Whoops - the ball is in the back fence! Help!

The legs, hips, shoulders even the upper arm must stop or at least pause before the moment of contact of racket and ball. If they don't, you get no spin and no directional control, both of which are necessary to keep your ball from over-reaching the baseline (or sideline). The reason that stopping the shoulders is so important is because of the stretch-shortening stored forces that you created during the lock and load phases of the stroke. Those stored forces are designed to deliver directional momentum (control) and angular momentum (spin) directly into the ball. What keeps the stored forces stored is the acceleration of the racket during the lag phase when the racket head, loaded down with its own inertia, is dragged behind the hitting hand. The inertia of the racket head keeps the stored forces bottled up until a few milliseconds before the moment of contact. At that point the shoulders start to decelerate releasing the stored forces all at once in an orgasm of energy, spin and control injected directly into the ball. Without the participation of the non-hitting hand, the natural tendency to complete a rotation once started leads to over-rotation and the stored forces that are essential for directional control and spin are only released after the ball is already gone.

Now the purpose of the non-hitting arm in this context is to stop the rotation of the shoulders. In the one-handed backhand (topspin/slice/volley), you stop the shoulders by reaching behind your body with the non-hitting arm just before the moment of contact. In the early phase of this move the counter-rotation increases the speed of rotation of the shoulders, but as the off-side arm reaches the limit of its extension, it decelerates and stops the acceleration of the hitting arm, thereby releasing the forces stored there. The ability of the non-hitting hand to stop racket acceleration is why pros with great one-handed backhands seem to throw the non-hitting hand behind them to the very limit of shoulder flexibility (see above). On the forehand side, the non-hitting arm crosses by the hitting arm tying you in a kind of knot. In both cases the non-hitting arm is thrown into counter-rotation to the hitting arm just before the moment of contact, first reinforcing then interrupting the forward acceleration of the stroke and thereby releasing the stored forces.

The Cartwheel

In the serve, the power move begins after the pose when the tossing arm and shoulder are pulled down, and the hitting shoulder comes up in a clockwise (if you are right-handed) rotation of the body around an axis that resembles a spear through the breast-plate. This cartwheel (or shoulder-over-shoulder) phase of the serve is analogous to the lag phase of the groundstrokes. It begins when the legs explode from below, and the tossing arm is pulled down from above. So the non-hitting arm starts this power move of the serve, but it also finishes it. One could complete the cartwheel with the tossing arm ending up behind the server, but instead, the non-hitting arm is snatched to the chest just before the racket reaches its zenith. Abruptly stopping the tossing arm stops the cartwheel rotation of the shoulders and releases the stored forces, injecting them into the ball (sound familiar?). If you allow the non-hitting hand to come down below your waist, you will over-rotate, and neither spin nor control will ever reach the ball. The cartwheel motion of the shoulders also contributes significant power to the two-handed backhand.