## 4 Discussion  
The hypothesis of this research presumed that a 8-week training program that included a SSG twice a week, 4 vs.4+GK would improve the VO\({}_{\text{2 max}}\) level, and 10 m and 20 m sprint and agility with and without a ball, for U18 football players. Our findings showed that the SSG group has a greater improvement in aerobic fitness and agility than the conventional training group which further improves the speed indicators. There is research in which it is shown that the level of the effort capacity of football players can be correlated with their physical performance during a match, including parameters such as total distance, accelerations, decelerations and total distance in high-speed running and very-high-speed running [36; 37]. However, only few papers analyze the correlation between the physical condition of players and their physical and technical performance in SSGs. The findings of these studies are important for coaches because the \"training load\" of the training session should be designed individually to improve performance and avoid excess fatigue and overtraining. In the research of [PERSON] et al. [38], they compared the physical requirements of two SSG formats: 4 vs.4+GK (goalkeeper) and 8 vs.8+GK. It has been shown that 4 vs.4+GK is more demanding in relation to repetitions and fatigue, the development of actions being based on muscle strength having as a substrate the anaerobic energy path, the perceived effort and the number of technical actions, while during 8 vs.8+GK games players run more at a high intensity. In addition, the performance of repeated jump tests appears to correlate with distances covered at high intensities in 4 vs.4+GK games. It is therefore possible to use 4 vs.4+GK games to develop the football skills of players. The results of our study on the influence of a 4 vs.4+GK SGG on VO\({}_{\text{2 max}}\) optimization align with the results of previous studies that aimed to optimize the functional capacity of soccer players by testing with SGGs and different training variations depending on the type of effort. For the players from the experimental group after implementing the 4 vs.4+GK SGG twice a week, on Wednesday and Saturday, the VO\({}_{\text{2 max}}\) values showed an increase of 10.34%, reaching 61.44 \(\pm\) 2.66 mL/kg/min, with the increase being statistically significant (\(p\) < 0.0005). At the same time, the control group that followed a training program based on aerobic endurance interval training on Wednesday and a match on Saturday had an increase in the VO\({}_{\text{2 max}}\) value with only a 0.30% progress rate being considered statistically insignificant (\(p\) > 0.05). The results shows that elite junior football players are more motivated during SSGs to exert aerobic efforts under game-specific conditions, compared to when undergoing interval training. We believe this may be due to the fact that the effort and type of activity in SSGs is very close to that encountered during a match. This can motivate players to obtained a better experience, sensations and feelings, compared to those obtained via interval training [22; 39]. It can be observed that after four weeks of training with SSGs, the VO\({}_{\text{2 max}}\) level of elite junior soccer players increased from 55.6 \(\pm\) 3.4 mL/kg/min initial testing to 59.7 \(\pm\) 4.1 mL/kg/min during final testing. The results of the 10 m sprint tests reveal that the experimental group's performance increased significantly (6.70%) (\(p\) < 0.0005), and the control group's performance also increased significantly (\(p\) < 0.0005), but at a slower rate (only 4.52%), compared to the experimental group. At the end of the exam, there was no significant difference between