The Impact of the Preparation Period on Endurance at Football Players U16

The main aim of the research was to identify a level of quantitative changes of the endurance with U16 football players under the infl uence of the programmed football training of a six weeks preparation period. The training programme covered forty-four training units. The research was made on a sample of 120 football players U16. To estimate the endurance three tests have been used: Cooper test, Running 15 m long distance for 90 s, and Pin running persistence. In the area of comparative statistics, we used discriminant parametric procedure t-test for big paired samples. It can be concluded that there are statistically signifi cant diff erences in all three variables to estimate the endurance. This confi rmed the hypothesis that the expected signifi cant positive quantitative changes of endurance infl uenced by the proposed model of training in preparation period with football players U16. The authors were guided by the fact that this kind of training program in preparation period is very eff ective in terms of raising the endurance level with football players U16. The obtained results can be directed towards innovation plans and programs in the preparation period, and the adaptation of the same needs of the respective population.


Introduction
Football is a sport that is characterized by numerous and varied complex dynamic kinesiology activities that are characterized by a large number of cyclic and acyclic movements (Gardašević, & Goranović, 2011;Gardašević, & Bjelica, 2013;Sermaxhaj, Popovic, Bjelica, Gardasevic, & Arifi , 2017;Corluka, & Vasiljevic, 2018). It is evident that all four moments of play (Gardašević, Bjelica, & Popović, 2015;Gardasevic, 2015), possession of the ball, the opponent's possession of it, the transformation aft er winning the ball and the transformation aft er losing the ball depends on the ability of players to perform certain movements of varying intensity, in diff erent directions and the diff erent sections of the fi eld Gardašević, Bjelica, & Vasiljević, 2016a ;Gardasevic, Bjelica, & Vasiljevic, 2017a;. Th ey must have developed basic and specifi c motor abilities (Vasiljević, Gardašević, & Bojanić, 2013;Bjelica, Popović, & Gardašević, 2016a). One of the basic motor skills, which should be at a high level, is endurance. Most of the elements in football game, especially those with the ball, are very complex (Gardašević, Bjelica, & Vasiljević, 2016b;Gardasevic, Bjelica, Milasinovic, & Vasiljevic, 2016). For their improvement and impeccable application in the game, it is necessary fi rst to have the whole motor preparations Gardaševic, & Vasiljević, 2016). Th e physical strength has a great importance in football (Gardaševic, & Bjelica, 2014a;Gardasevic, & Bjelica, 2014bBjelica, Popović, & Gardašević, 2016b. A specifi c strength with football player is refl ected by the strength refl ection while jumping, the pushing strength with sprint, strength of stopping and pushing while changing the moving direction, strength of kicking by foot and with a head, strength of throwing the ball with a hand, stability on the ground and in the air, in duels (Gardaševic, & Bjelica, 2014). One of the factors that aff ect the strength is the football players is their age (Bjelica, 2003;2004;2005). In child's development the strength increases with increasing a muscle size. Psychomotor strength, primarily static and repetitive, according to some authors is 50% innate, and Th e endurance of football players may be the most important ability (Gardašević, 2010). It is defi ned as the ability to perform an activity for a long time period without reducing the eff ectiveness of this activity, i.e. the ability of endure a physical eff ort for a long time. Th e coeffi cient of inheritance of this ability is 70-80%. Th e endurance is based on the effi ciency of the functioning of the regulatory mechanisms which are manifested in energy reserves (ATP, creatine phosphate and oxygen) and functional quality of energy potential (energy processes). We distinguish three types of endurance to a man: Aerobic endurance (from 5 min to several hours), Anaerobic lactate endurance (from 3 to 5 minutes) and Anaerobic alactate endurance (from 15 to 20 seconds). Th e main objective of this study was to determine the level of quantitative changes of endurance in football players U16, under the infl uence of a programmed football training which included one preparatory period of forty-two days.

Methods
Th is was a longitudinal study with an aim that in the two time-varying points determine quantitative changes of endurance in football players (15 year ± 6 months) under the infl uence of programmed training process, which included a summer preparation period for the competition season in a unique cadet league of Montenegro and the cadet league middle region of Montenegro. Th e training program lasted 42 days and was carried out on the auxiliary football fi eld of FC Sutjeska Niksic. Th e training program included 44 trainers units, within which 8 friendly matches were played. For data processing only the results of those respondents who have undergone a complete program of work and who have joined the initial and fi nal measurement are taken. Th is study included a sample of 120 young football players U16 of 4 teams, all from Niksic. Before programmed work all respondents had passed medical check-ups to make sure they could access the training process. When selecting the instruments (tests) it was taken into account that they meet the basic metric characteristics Gardaševic, Bjelica, Georgiev, & Popović, 2012;Bjelica, Gardasević, Georgiev, Popović, & Petković, 2012), which means the appropriate age and objective material and spatial conditions. For the assessment of endurance the following tests were used: 1. Cooper test (MCPT), 2. Running 15 m long distance for 90 s (MRLD), 3. Pin running persistence (MPRP).
Considering that these are a cadet age players (15-year olds ± 6 months), in a sensitive period of psychophysical development, program is tailored specifi cally to their age, taking into account the time spent in the previous training process. Time structure of the training ranged from 60 to 120 minutes, depending on the goals and objectives of the training unit and it was divided into 3 phases:  Introductory-preparatory part (25-30% of the duration of training)  Th e main part (60-65% of the duration of the training)  Th e fi nal part (up to 10% of the duration of training) In the introductory-preparatory part of the training the emphasis was on raising the operating temperature in children. As a tool a various elementary games with a ball were used that enabled work on the elementary basics of technique and tactics, also the various polygons with exercises coordination were used. A variety of games and exercises to increase joint mobility and strengthen muscles also applied at this stage. At the fi rst stage of the main part of the training the intensity is slightly increased compared to the warm-up phase and the training program was implemented through a variety of ball games. With a game method the respondents were taught and practiced football skills through a large number of repetitions. At the second stage of the main part of the training the players mostly had a free game on two goals that allowed them a creative activities and highlight of individual, imagination, independent thinking and hard work, applying the elements that teach by the method of the game from the fi rst stage of the main part, and thus strengthening the willing quality. At this stage of the training the intensity was the greatest. At the fi nal part of the training the task was lowering the physiological curve to an optimum level, and low-intensity activities were used: stretching and relaxation exercises, competitive game of penalty kicks, free kicks.
Data obtained from the survey were analyzed using descriptive and comparative statistics. In the area of descriptive statistics for each variable both in the initial and the fi nal state central and dispersion parameters were processed as well as measures of asymmetry and fl atness. Th e hypothesis of normal distribution of results was tested on the basis of Kolmogorov and Smirnov test. In the area of comparative statistics, to determine diff erences in the variables used to estimate the endurance at the start (initial state) and at the end (fi nal state) of the training program in the preparation period, we used the discriminative parametric procedure t-test for large dependent samples.

Results
In Tables 1 and 2 (Table 1). Central and dispersion parameters of variables for estimation of the endurance in the fi nal measurement showed the following values (Table 2) By analyzing the central and dispersion parameters of variables for estimation of the endurance in the fi nal stage-it can be noticed that here as well the values of arithmetic means in all three variables are at a higher level than in the initial state. Th e results belong to extremely homogeneous sets in all three variables. Th e values of skewness and kurtosis are in the range of -1 to +1, which means that the inclination and elongation of the results do not deviate statistically signifi cantly from the normal schedule. Th e values of Kolmogorov and Smirnov test shows that the results are normally distributed in all three variables.
To determine the statistical signifi cance (signifi cance) of differences in arithmetic means (partial quantitative changes) of variables for estimation of the endurance, the t-test was applied to for large dependent samples. Th e values of t-test were on the level of signifi cance (Sig.) from 0.01 (p≤.01) in all the variables for the evaluation of endurance. Th e diff erences of arithmetic means of the initial and the fi nal measurement of variables for evaluating endurance are shown in Table 3.
Based on the results gained it can be noted that there are statistically signifi cant diff erences in all variables for estimation of the endurance, and therefore can be said that there was a statistically signifi cant positive partial eff ects of the training program in the preparation period, and the t-test values were signifi cant at the reliability level p <.01 for all variables for estimation of the endurance.

Discussion
On the basis of the obtained parameters it can be concluded that the statistically signifi cant partial quantitative eff ects (changes) in all the variables for estimation of the endurance obtained as a result of the training program applied in the preparation period. Th e method of work that has been applied in this training program abounds running with varying intensity, so that the positive transformations are not unexpected (Gardaševic, & Bjelica, 2014;Gardašević, Bjelica, Popović, & Milašinović, 2016;Gardasevic, Popovic, & Bjelica, 2016;Gardasevic, Bjelica, & Vasiljevic, 2017b). In this age it comes to an increase in biological growth and development of muscles, increase of muscle cross-section, which can certainly contribute to positive results (Gardasevic, Bjelica, & Vasiljevic, 2016). Based on the results of t-test for large dependent samples, with the variables for estimation of the endurance the statistically signifi cant diff erences were determined in all pairs of variables between the initial and fi nal states, at the level of statistical signifi cance (signifi cance), p <.01. In this research the authors were guided by the fact that such a training program of work in preparation period is a very effi cient way of working in terms of raising the level of endurance with football players U16 (Vasiljevic, 20017). Th e authors conclude that the summer period of 42 days, at football players U16, with such training work program, is optimal for lift ing the endurance to the level required for the competition. Th e gained results can be directed towards innovation of plans and programs of work in the preparation period, and adjusting the same to the needs of the population concerned.