Chapter eight
“The theory of push lines”. The four unescapable push lines and the five fundamental principles of modern tennis playing technique.
The optimal execution strokes.
The theory of push lines places the five fundamental principles at the service of a single logic which analyses and connects the unescapable push lines with each other.
The four push lines are to be considered inescapable and linked together for all the optimal execution strokes and they allow these to be carried out in accordance with the five fundamental principles, in an essential way, with the minimal effort needed to obtain the best push impulse to transfer to the ball.
This theory aims at bringing out the technical quality of the player, which is determined by the precision in placing the shots, the travel and rotation speed of the balls played and by clean and essential gestures, made with smooth and natural movements.
In this way, it is easier for the player to meet the quick balls served by his opponent, he avoids wasting precious energy, and he can keep up his best psychophysical level longer; moreover, he can avoid certain injuries which are often caused by an inaccurate technique.
It is important to bear in mind that the player finds himself experiencing a situation determined by external factors and, exception made only for the serve in which he is the one to determine it, he must hit a ball coming from the opponent’s court and which presents a number of variables such as the trajectory, the point of rebound and the travel and rotation speed, sometimes modified by the wind.
This theory primarily analyses the strokes with an optimal execution of the technical movement and, secondarily, it identifies the changes to apply to the movements for strokes where the execution is modified according to specific external variables.
The optimal execution strokes are those which, because of a low incidence of external variables, enable to optimize the synergic action and they are executed with the player assuming an optimal position concerning the precise ball-racket impact point and the precise rebound point that he wants to obtain in the opponent’s court.
The player’s optimal position, for rebound strokes and for forehand and backhand volleys, one or two-handed, is behind and slightly to the side of the precise ball-racket impact point and simply behind in the serve and smash.
During the player’s synergic action, this position allows the forward movement of the racket along a hypothetical track which takes it to the precise impact point with the ball, in the direction of its rebound point in the opponent’s court, by applying the logic of the push line theory in full observance of the five fundamental principles.
(the figure shows the three ideal positions: 1 – forehand with rebound and volley, 2 – backhand with rebound and volley, 3 – serve and smash always in the presence of the hypothetical track with the three reference points)
The strokes with a modified execution are all those which are executed when the player is not in an optimal position, as we have just described.
The four unescapable push lines.
The body of the player moves along the first two unescapable lines during the execution of the technical movement which brings the racket to hit the ball.
The string face of the racket moves along the third unescapable line, whereas the fourth line concerns the orientation of the racket, which determines the ball trajectory.
The first inescapable push line is the line along which the barycentre axis of the player’s body moves and it represents the main driving force behind the synergic action which develops the kinetic energy.
The barycentre axis of the body is perpendicular to the ground, it coincides with the spot on the ground placed in the centre of the player’s support area, and it determines his balance.
(figure showing the barycentre axis of the body with the indication of the spot in the centre of the support area on the ground and of the line which is perpendicular to the ground which identifies it)
During the synergic action developed in executing the technical movement, the player shifts his weight force from one foot to the other, and in doing so he moves the barycentre axis of his body on the first unescapable push line.
(figure showing the shifting of the barycentre axis of the body from one foot to the other, with the indication of the first unescapable push line)
The second unescapable push line is the line traced hypothetically in the air by the hand, during the closing movement which brings the racket to hit the ball.
It should correspond to the line on which acts the point of greater pressure of the hand on the handle, passing through the barycentre axis of the racket, as described in principle number four.
(figure showing the hand and racket moving towards the point of impact with the ball, with the indication of the second unescapable push line)
The third unescapable push line is the line along which the racket face moves, from the beginning of its movement towards the area of maximum force and maximum sensitivity, where it hits the ball, until the moment the ball leaves the string face.
(figure showing the movement of the string face towards the point of impact and the third unescapable push line)
The fourth unescapable push line is parallel to the string face, when it finds itself in the area of maximum force and maximum sensitivity at the moment of impact, and it indicates the direction taken by the ball after leaving the racket.
(figure showing the fourth unescapable push line which is perpendicular to the string face at the moment of impact)
Compensating and optimizing the push impulse.
Let us analyse what happens during the ball-racket impact, in optimally executed strokes and let us try to establish objectively how we can improve this event to our advantage.
The player’s synergic action transfers a push impulse to the racket, by utilizing the body segments as levers and the barycentre axis of the body as fulcrum.
Thanks to the peripheral speed of the string face, when it hits the ball, the racket sends it on its way with a push impulse, a variation in motion or dynamic effect.
(figure showing the centre, or fulcrum, determined by the barycentre axis of the body, around which rotates the racket with the direction of the peripheral speed and the width of the radius of the great lever)
(the great lever is formed by the chain of segments of the biological human machine which, by developing kinetic energy, contributes towards giving speed to the racket face; the segments are: shoulder, arm, forearm and hand)
We only have two ways of optimizing the push impulse:
- by utilizing the maximum width of the radius of the great lever;
- by developing a greater peripheral speed.
For this precise reason, when searching for the greatest push impulse, arm and forearm must be in line during the ball-racket impact, thus forming a single lever with a certainly longer radius than the one you can obtain by flexing the forearm on the arm; a vigorous synergic action of the player will allow a quicker technical gesture thus increasing the peripheral speed of the string face.
With the factors described above and with a correct positioning of the player’s feet the following situations occur:
- In forehand and backhand strikes, two-handed, on rebound, on half volley, and on volley very far from the net, the barycentre axis of the body acts as a fulcrum in the rotation of the “great lever”, and it moves along the first push line which is oriented on a diverging diagonal with respect to the second push line, because it shifts from one foot to the other.
In this way, the two actions executed simultaneously, act in compensation and optimization by virtue of the alignment of the second push line to the fourth, in the direction of the precise ball-racket point of impact and of the exact rebound spot of the ball in the opponent’s court.
(when referring to the fourth push line, show the figure illustrating the shifting of the barycentre axis and of the rotation of the body on it, in compensation and optimization of the alignment of the second push line to the fourth, for the above mentioned strokes, indicating the correct feet position and the direction of the body rotation)
In this way we obtain that, in full observance of the logic of the theory, the second push line acts together with the third, optimizing the forward movement of the racket along the hypothetical track which leads it to the precise point of impact with the ball, thus placing them in line with the fourth push line, in the direction of the rebound point of the ball in the opponent’s court.
(figure showing the track and the orientation of the four unescapable push lines for the strokes we just mentioned)
- In the situation of a right-handed player with a correct position of the feet in line with the net, executing a one-handed backhand, the barycentre axis of the body and the first unescapable push line move towards the right side of the player shifting from one foot to the other.
The arm-racket lever together with the second and third push lines proceed in a pendular movement from the left to the right of the player, with his right shoulder acting as a fulcrum.
The slight compensation and optimization is carried out by the axis of the shoulder, which utilizes the barycentre axis of the body as a fulcrum.
In the open position the axis of the shoulder is slightly turned to the left and the right shoulder is in a slightly advanced position compared to the left shoulder.
At the moment of ball-racket impact the axis of the shoulder is perpendicular to the string face and in line with the fourth push line.
At the end of the movement the axis of the shoulders is slightly turned to the right and the left shoulder is in a slightly advanced position compared to the right shoulder.
(figure showing the barycentre axis of the body which moves along the first push line, and the action of compensation and optimization of the axis of the shoulders with the second and third push lines, by placing them in line with the fourth, indicating the correct foot position.)
- For the flat serve, in slice and lifted and for the volley and rebound smash there is only the mechanism of optimization without compensation.
The barycentre axis of the body shifts forward to the foot which is opposite to that of the arm-racket, while the great lever, with a swirling movement, the lift of the shoulder and the stretching of the arm and forearm upwards, brings the second and third push lines higher and forward, moving them exactly along the prolongation of the barycentre axis of the body, thus placing them in line with the first and fourth.
(figure showing the shift of the barycentre axis of the body and the alignment of the four unescapable push lines in the flat serve as a general example)
The barycentre axis of the body is, in actual fact, incorporated in the action of the great lever, which impresses a peripheral speed to the face of the racket, with the perfect synergy of all four unescapable push lines, turning these shots into real whiplashes to the ball thus giving them an exceptional forward speed and possibly an exceptional spin.
- Forehand and backhand volleys near the net, compared to rebound strokes, have the same theory logic but the direction of the compensation and optimization action motion is inverted.
In the forehand volley of a right-handed player, during the stroke conclusion, the second and third push lines move forward and to the left whereas the baricenter axes of the body acts in an opposite way, thanks to a long step taken quickly who shifts forward and to the right by the player following the first push line; in the backhand volley the action is specular.
(figure showing the shift of the barycentre axis of the body and the orientation of the relevant unescapable push lines for the forehand and backhand volley shots, indicating the correct foot position and the hypothetical track)
Spins.
It is possible to give the ball various forward speed levels and three different types of spin; because of the Magnus effect, flight trajectories depend not only on the type but also on the amount of spins.
According to logic of the theory of push lines, in relation to principles number four and five, regarding grips, the type of spin given to the ball depends on the inclination of the second and third push lines compared to a horizontal plane and to the string face placed in a vertical position.
The inclination oriented from low to high corresponds to the topspin, the one oriented from high to low corresponds to the backspin.
With a lateral inclination towards one of the two sides you get the ball to spin on a vertical axis, called slice serve, but also commonly called sidespin in forehand and backhand strokes.
(diagrams representing the three types of spin with the angle of the second and third push lines)
(figure of the flight trajectory of the ball obtained with a flat stroke)
(figure of the trajectory of the ball obtained with a topspin stroke)
(figure of the trajectory of the ball obtained with a backspin stroke)
If there is no inclination, with the second unescapable push line perfectly in line with the third and fourth, you obtain a flat stroke, without spin, thus transferring to the ball the impulse of forward push and of forward motion speed.
(diagram on cartesian axes of a flat stroke)
And so, by following the dictates of the fourth and fifth principles, in full observance of the logic of the theory of the four unescapable push lines it is possible to obtain different rotation levels with many trajectories and dynamic spins to the ball.
On the other hand, when searching for a precise dynamic spin to give to the ball, if a conflict of logic arises between the theory of four unescapable push lines and one of the five fundamental principles, the result is neither optimal nor is it guaranteed; the example that follows concerns a technical forehand on rebound error, which is quite common with amateurs, and helps to clarify this concept.
When, by using the forehand grip you try to hit a flat stroke with backspin, or worse still with topspin, you encounter many problems in giving the ball an upward spin and in giving it an accurate trajectory, in particular during rhythm changes, which require a quick acceleration of the string face towards the point of impact.
This is because the push line of the point of greater pressure of the hand on the handle, indicated in the fourth principle, does not coincide and is in conflict with the angle of the second unescapable push line, and the hand cannot find a comfortable, strong and natural grip during the ball-racket impact.
(figure showing the conflict between the two lines)
Advantages that the forehand offers in comparison to the backhand.
I conclude this chapter by listing the many advantages that the forehand offers in comparison to the backhand:
- a wider radius of the “great lever” as the barycentre axis of the body rests on the foot which is opposite to the arm-racket side during the impact;
(3 figures showing the great lever of the single and double-handed forehand and backhand with their different lengths)
- the utilization of the body’s front muscular system, which is more powerful, allowing a greater acceleration of the string face peripheral speed;
- the double action of the fulcrum and pivot hypothenar, which enables to give an additional whiplash to the ball, with the passive flexion of the wrist, obtained at the beginning of the closing action, by the rapid forward movement of the arm-forearm lever, with relaxed wrist joint, and at the end of the same action, the active stretching of the wrist joint, and at the same time the pronation and the rotation of the humerus;
- the front view of the court which gives a better view of the ball to hit, of the spot in which to make it rebound and of our opponent.
Therefore the forehand rebound is to be preferred to the backhand, even to the one played two-handed, because this last one is in any case at a disadvantage as far as points 1 and 4 are concerned.
These are the reasons which induce professionals, whenever possible, to use footwork to go around the ball in order to play forehand instead of backhand.
I advise everybody to do the same.