All subjects were members of the teams playing in the First Croatian Junior League. In this league, there are 12 clubs, and each club has about 25 players in the team. Because this study was financed by the Croatian Football Federation, all players were at our disposal. Only 8 clubs had all the necessary facilities and equipment to participate in this study. We then divided these 8 clubs randomly into 2 groups-the EG and the CG, each consisting of 100 players. But, for the players to be tested at the end of the study (final testing), they had to have completed 75% of the entire training process and they ought to have played 85% of all official matches. Only 100 players (50 from the experimental and 50 from CG) were able to match these criteria. All the subjects were familiar with the SAQ training.
The study was approved by the Ethics Committee of the Faculty of Kinesiology, University of Zagreb. To be included in the investigation, each subject provided a written informed consent in accordance with the Helsinki Declaration. The participants were aware that they could withdraw from the study at any time.
Goalkeepers were excluded from the investigation following their morphological characteristics and motor ability differences (5,28). For field players to be included in this study, the following requirements were set-minimal number of games played during the past season was set at 20 (friendly or championship games), minimal attendance of 75% of training sessions in the past season, minimum of 7 years of soccer experience, minimum of 6 weeks of preseason period, and a similar beginning of the preseason training in all 8 clubs. The training regimen was composed of minimum 3 SAQ training sessions a week in compliance with the SAQ program (Figure 1, Table 4) for the EG. Each training session had the strength training and the conditioning part and the technical-tactical part. Also, a game was played each week as a part of the in-season period schedule. The mean (SD) age, height and body mass for the EG was 19 years, 174.78 (5.74) cm and 67.83 (3.37) kg, respectively, vs. 19 years, 175.09 (5.29) cm, and 68.18 (4.08) kg, respectively, for the CG.
The initial testing took place before the beginning of the in-season period (end of preseason), whereas the final testing was performed after 8 weeks of intervention with the SAQ training method. To prevent unnecessary fatigue accumulation, the players and coaches were instructed to avoid intense exercise for a 24-hour period before each testing session. Also, before each testing, the subjects performed a standard 25-minute warm-up. During testing, the air temperature ranged from 22 to 27°C. The testing always commenced at 10 am and was completed by 1 pm. The physical load at given intensities was monitored by heart rate monitors. All sprint tests were performed on a grass sports field, and the players wore soccer shoes to replicate the playing conditions.
The sprints over 5, 10, 20, and 30 m (SP5, SP10, SP20, and SP30, respectively) were performed from a standing start and measured by means of infrared photocells using a telemetric system (RS Sport, Zagreb, Croatia). Time was recorded in 100ths of a second, and the average value from 3 sprint attempts was taken into consideration as a final result.
Four Bosco Jump tests were used to assess muscle power of leg extensor muscles (Kistler, Quattro Jump force platform, Winterthur, Switzerland). The players had 2 preparatory measurements. An average of 3 measurements was used to represent the final result in the SJ, CMJ, maximal CMJ (MAX), and continuous jumps with legs extended (CJS).
During the investigation (8 weeks of the in-season period), the CG performed the traditional in-season training regimen, whereas the EG had an intervention with the SAQ training program. Also, the EG was required to perform 3 SAQ training sessions a week, on Monday, Wednesday, and Thursday. Thus, the program entailed, among others, 24 SAQ workouts, whereas the CG covered approximately the same volume of regular training. We considered that there was no difference in the training volume that would represent an important factor when comparing the effects of these 2 groups. Each SAQ session followed detailed components of training during the 8-week period (Figure 1).
The Kolmogorov-Smirnov test showed that data were normally distributed. The statistical power was 0.95, and the effect size was medium (r = 0.52). Interclass correlation coefficient (ICCRs) for all variables ranged from 0.66 to 0.85.
Results from other tests showed that the EG values improved compared with those of the CG but not enough for this improvement to be significant. The CG remained at the initial test result values or even aggravated their performance in the measured tests.
Furthermore, elite players are mostly characterized by reaction ability in the distances ranging from 5 to 10 m (25). Overall power performance is used in both attack and defense when goals are scored or defended. Similar studies found that a general distinction between the elite-level and less elite-level soccer performance is in the high-intensity running during a game, which in turn involves more sprints over shorter distances and faster reactions. Also, during a match, the overall distance covered ranging from 500 to 600 m comes from sprint actions (26), which happen every 90 seconds (27). The facts presented are in relation with this study and the results that show the improvement in tests that estimate quickness (SP5) and acceleration (SP10) of elite soccer players. Krustrup et al. (16) placed power performance parameters in direct dependency to soccer success and thus emphasized the importance of the SAQ training method as such. Furthermore, recent studies showed that jump test performance is also related to team success (1), whereas vertical jump height is related to short sprint performance (7,30).
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