Introduction

In jumping the player is producing vertical velocity for the center of gravity through plantar flexion in ankle, knee extension, hip extension, trunk, head and arm movements. During takeoff a key factor is to utilize all positive net impulse effects for a high vertical release velocity of the center of gravity of the player. Timing of the segmental movements is a real skill factor in jumping.

Jumping skills are most important for field player in moving header and for goalkeepers in all takeoff actions. The goalkeeper must be a skilled jumper, as many of the saves he will be asked to make will require a maximum jump to reach the ball. The majority of the jumps made by the goalkeeper will be performed using a one legged takeoff, as he often will be moving toward the ball at takeoff and it is faster to use the one legged takeoff. However, since a higher jump can usually be attained using a two legged takeoff, this takeoff is recommended for high shots near the crossbar. As soon as the ball has been released and a high shot is anticipated, the goalkeeper should deepen his crouch, and prepare for the jump by lowering the arms. From this position, the arms accelerate upward in the direction of the jump, and the trunk is also extended upward. The legs then forcefully extend in the direction of the jump, to project the goalkeeper as high as possible in the direction of the ball. The principle of maximizing the impulse at takeoff must be observed in this skill, so the goalkeeper will increase both the force applied at takeoff, and the time over which that force is applied. The range of the arm swing, trunk extension, and depth of crouch will all determine the height attained on the jump. As the goalkeeper lowers his center of gravity prior to takeoff by flexing the legs and flexing the trunk forward, and lowers his arms, he will increase the forces applied to the ground as he accelerates them upwards takeoff.

In the one legged takeoff, the goalkeeper takes a long step onto the takeoff foot, and both the arms and the free leg are accelerated upward just prior to the leg drive. The takeoff leg is then forcefully extended to drive the body upward in the direction of the ball. The goalkeepers and soccer players should be two footed, that is he should be able to takeoff from either foot and still reach maximum height.

Segmental contributions to the rise of the center of gravity in vertical jumps has been highest in knee extension (55 %), then plantar flexion of ankles (25 %). The role of trunk extension and arm movement has been about 10 % from both. For the coach it is important to recognize the priority of different joint and segment movements. If any of these joint actions are not used the output of jumping performance will not be maximal (Luhtanen 1978).

Jumping ability is important for field players in heading and goalkeepers in diving saving. A jump in match conditions can be executed with or without run-up. The take-off without run-up can start from a squatting position , erect position with counter movement or with preparatory movements by arms. The number of jumps in a match is on average 11-20 in a match and headers 9.9 + 5.7. The players jump for headers mainly after run-up. The rise of the center of gravity (C.G.) has not been measured in real football match conditions. The laboratory measurements from standing position indicated that the highest average heights of the C.G. reported in football were in squatting jumps 40.4 cm, counter movement jumps 43.5 cm and in vertical jump with preparatory arm movements 59.8 cm (e.g. Faina et al. 1988, Bosco et al. 1989, White et al. 1988).

The real meaning of jumping ability varies according to the game. In football, the good ability is needed but applied relatively seldom. In volleyball, the excellent jumping ability from physical point of view (explosive strength and jumping endurance) is a key factor.

The real match conditions require that the players can apply their jumping abilities according to the prevailing match situation. Then, the timing in jumping and technical heading performance are important.

A Model to Evaluate Jumping Performance

A model to evaluate vertical jumping performance can be created in different ways. From point of view of biomechanics the total height reached for a header after take-off in jumping is due to e.g. body height, take-off force and duration of the applied force, vertical release velocity produced according the principle of force impulse and body position and movements for heading in air (Figure 9).

Main attention should put on the mechanics and mechanism of take-off performance.

Figure 9 . A model to evaluate jumping performance

Force Impulse Production

The force impulse production for the release velocity in vertical direction can be evaluated as vertical net impulse of the applied force or indirectly evaluating the amount of total energy observed in different phases, stored elastic energy during impact or eccentric phase, work done during ascent or utilization of the elastic energy and mechanical energy losses due to the inhibitory factors.

Several factors can be identified influencing on the force production during take-off movements in different body segments, joints, muscles and tendons from point of view of neuromuscular mechanism:

* muscle strength
* muscle length
* speed of muscle lengthening
* muscle tension
* joint angle
* angular velocities of joints
* order of the angular velocities of the joints
* order of the movements in body segments
* timing and summation of the forces in body segments
* duration of the segmental movements
* exhibitory and inhibitory reflexes

From mechanical point of view for the take-off performance can be applied the principle of energy conservation, energy production from external and internal forces and energy transfer from energy state to energy state. Basically, this means the ability of the player to utilize the energy of run-up (due to the velocity), elastic energy (stored in different tissues, shoe and surface), transfer of the kinetic and elastic energy into the potential energy (rise of C.G.) and transfer of the energy between body segments in an optimal way.

Development of Jumping Training

The influencing factors in reaching maximal rise of C.G. jumping performance have been explained in the text.

In developing training process for progression of the jumping ability, it is important to identify the strengths and weaknesses of the players inside of the influencing factors in a priority order. Then the process includes:

* pre-testing of the player
* pre analysis of his jumping performance
* planning of individual training program
* training in proper guidance of the expert coach
* follow-up of the effects of the planned training and applied training
* analysis of the special training and whole season
* feedback for the new season and its special training

In analyzing individual players according to tests, it is essential to evaluate players as individual in their:

* strengths in jumping
* individual faults technically
* individual deficits
* possibly limiting factors
* trainable factors

The planned individual training programmes have to be individual according to analysis and follow-up in:

* volume
* intensity
* quality

In individualizing training programmes, selected scientific principles of the progressive training can be applied combining with strength and speed training:

* force-velocity curve
* power-velocity curve
* power-load curve
* jumping height-load curve

Figure 10. Jumping height - load curves of three players

When studying individual force-velocity curves in order to gain players' jumping height, it is important to try to analyze:

* strength level
* speed level
* muscular elasticity level

Player 1 had (Fig. 10) a low rise of C.G. in jumping test and high isometric leg strength level. Player 3 had a high rise of C.G. in jumping test and low isometric leg strength level. Practically these results mean different training programmes for the player 1 and 3.

Jumping Conclusion

It can be concluded that the training principles for football players could be clear if only to maximize their jumping abilities through basic strength and explosive leg strength training. Different multi-step jumping exercises and plyometrics training should be included in the programme.

For jumping strength training should be applied progressive principles as follows:

* individual
* versatile
* differentiation
* loading
* repetitions
* series
* duration
* recovery
* optimization

A key factor for players and coaches is that how much time to spend only for jumping training. It has to be integrated at least with speed training. The value of combined speed, jumping, agility, co-ordination and skill training is the highest for the total development of top players.