This is an excerpt from Soccer Speed by Richard Bate & Ian Jeffreys.
In learning optimal techniques for performing the various movements in the target classifications, players need to focus on target mechanics. In other words, effective movement needs to be based on sound mechanical principles. This foundation ensures that the technical model maximizes the player's performance potential.
In building up these mechanical models, we also need to revisit the target functions - that is, exactly what the player is trying to achieve. In initiation and actualization movements, the aim is to maximize speed performance, which (as highlighted in chapter 2) depends largely on the player's ability to produce and direct force. Therefore, technique needs to optimize the player's ability to place his or her body in the best position to produce force and direct it in the appropriate direction. Therefore, this kind of technique must be part of technical models for initiation and actualization movements.
In transition movements, on the other hand, the requirements are quite different. Here, the aim of the movement is to place the body in the optimal position from which to read, react, and perform a subsequent initiation movement. Thus the emphasis is not necessarily on speed but more often on control of the movement. While in transition, the player does not know what will happen next in the game and therefore cannot predict various aspects of subsequent movement, such as the type of movement required, the direction of movement, the timing of movement, and the skills that the player may be required to demonstrate.
Given this reality, the player must be able to maintain a position of stability during the movement - a position from which he or she can optimally apply a subsequent initiation movement. Therefore, even though the ability to perform these movements at speed is preferred, technique must not be developed in a way that compromises control.
What Is the Mechanical Basis of Acceleration?
Again, as highlighted in chapter 2, acceleration is intricately linked with the ability to apply force. Indeed, as Newton's second law dictates, acceleration is directly proportional to the force applied. However, sheer force alone does not totally explain effective acceleration technique. Force also requires an appropriate directional element, which means that good technique allows a player to maximize his or her force potential - and therefore acceleration potential - in a game situation.
In essence, effective acceleration takes place from a point of instability. Whenever a player's center of mass is placed ahead of his or her base of support, the player assumes an acceleration posture in the direction of the mass. Placing the center of mass ahead of the base of support allowsthe player to apply force down and back into the ground, thus enabling him or her to accelerate in the opposite direction. Indeed, the direction of the player's center of mass at any given moment naturally dictates the direction of his or her subsequent acceleration.
Force applied directly through the center of mass allows the player to maximize straight-line force because all of the force can be used to generate effective acceleration. In contrast, applying force away from the center of mass results in rotation, and the degree of rotation depends on how far from the center of mass the force is applied. Rotation is counterproductive to speed, and where possible, the aim should be to assume a straight-line posture, allowing force to be applied in a straight line during acceleration and maximum-speed running. Maintaining such posture as movement commences and develops requires a player to use considerable strength and stability.
Figure 3.1 shows a model of acceleration running with a degree of body lean and identifies the importance of straight-line forces.
What Is the Mechanical Basis of Maximum Speed?
The major difference between the mechanical requirements of maximum-speed running and those of acceleration involves ground contact time. As highlighted in chapter 2, the player needs to exert high levels of force; however, as the player moves through a sprint and gets progressively faster, ground contact time decreases, until it reaches a minimum as the player reaches his or her maximum speed. During acceleration, ground contact time allows the player to exert force both horizontally and vertically, but at maximum speed, because the body already has a high degree of horizontal momentum, the critical aim of ground force is to overcome gravity, thus allowing the player to take an optimal stride length. As a result, the vast majority of force at maximum speed is exerted vertically. This difference affects the player's posture, which is far more upright during high-speed running. It also affects the need to exert force as rapidly as possible, creating a high degree of dependence on the stretch - shortening cycle (see chapter 2).
Figure 3.2 shows a model of maximum-speed running, in which the posture is more upright, again demonstrating the importance of straight-line forces, and with the point of foot contact just in front of or underneath the center of mass.
What Is the Mechanical Basis of Stability?
Whereas acceleration requires a degree of instability, that type of posture is inefficient for transition movements, in which stability is crucial. Stability relies on the relationship between three main factors: the player's base of support, center of mass, and line of mass.
A soccer player's base of support refers to the area between the player's feet - and in simple terms, the greater the base of support, the more stable the player. Similarly, increasing this area in the direction of any oncoming force increases the stability in that direction. Widening the base of support also increases the player's stability, though beyond a certain optimal point the player's feet will be positioned too widely to effectively apply force, which is of course crucial for initiating any subsequent movement.
Stability also depends upon the height of a player's center of mass.The center of mass refers to the point around which the body's mass is equally distributed. In general, the higher this center is, the less stable the player becomes. As a result, the player can often gain stability by lowering his or her center of mass. As with base of support, however, an optimal point will be reached; in other words, if the player goes too low, his or her force-producing capacities are significantly reduced.
The third factor is known as the line of mass - effectively, the line drawn perpendicularly from the center of mass to the ground. The closer this line is to the middle of the base of support, the more stable the player is.
Again, for transition movements, stability is crucial, because it provides a position from which the player can effectively read and react to the game and perform any required movement or skill. Therefore, players need to develop technique that optimizes stability yet retains their capacity to apply subsequent force for any initiation movements.
Read more from Soccer Speed by Dick Bate and Ian Jeffreys.