## 4 Discussion
### Outcomes Measured  
Concerning the effects of INT in youth injury prevention and performance, it was suggested that dynamic stability can be improved [19; 21; 25; 28; 32] with an INT program. Notwithstanding, most studies reported improvements in this outcome. While two studies [23; 27] did not find changes, possibly by the cause of the training, it did not have the magnitude or stimulus required to enhance this outcome [23; 27], also possibly due to a low player attendance in the training sessions [27]. When the coordination of performing fundamental movement skills was assessed, we found some contradictory results. While significant changes after an INT protocol were reported in two studies [19; 20], one study [26] observed non-significant between-group changes. Again, an insufficient application of exercise could give an explanation to these results as the authors themselves indicated. There might be a dose response relationship for improving the fundamental movement skills with INT [26]. By taking a closer look at this study it was found that the training protocol consisted of only six exercises focused on hamstring strength, pyometrics, and dynamic stability. Nevertheless, there were no specific coordination exercises including fundamental movement skills. Furthermore, the same tendency can be observed with the sport-specific skills. One study [31] did not report between-group differences. Subsequently, an INT program of 15 min per session composed of 10 exercises focusing on strength, pyometric, and dynamic stability training was accomplished. It also concluded that the training volume and intensity for each of the exercises were too low to result in performance improvements. It is necessary that at least 20 min of INT replace the ordinary warm-up exercises used by the team [31]. As previously reported, there is also a controversy in strength and pyometrics after a neuromuscular training protocol. Further, three of five studies found positive changes in strength [21; 23; 24], while the remaining of two [27; 31] did not report any differences between groups. One possible explanation to this lack of effect could be attributable, at least in one of the studies [27], to a low training adherence (59.6 \(\pm\) 14.3%). It is assumed that a higher adherence to the training program would be necessary to improve this outcome [27; 31]. Along the same line, non-significant changes between groups were found in pylemetric tests after a period of INT in two studies [27; 32]. This was probably due to a combination of the lack of stimulus and low adherence to the training program [27; 32]. Moreover, contradictory results were found once more with respect to agility and speed tests. Most of the studies did not report significant changes between-groups in agility [23; 27] or speed [27; 29] performance. As it was described above, it appears that the adherence to the training programs and training stimulus should have been greater in order to enhance agility or speed performance [23; 27; 29]. Notwithstanding, another possible explanation of the discrepancies in this outcome is the number of contents performed. It has been suggested that performing a 15 min INT program, two times per week, training on only strength and dynamic stability contents [23; 27; 29], are not enough to improve agility and speed performance. Fatigue resistance was the only INT content that improved in the three studies, which measured this capacity [23; 24; 29]. Therefore, it can be suggested that an INT program can improve this outcome in young athletes. This can happen after a period of training of 8-12 weeks with two/three sessions per week focused on around 15 min training of dynamic stability and strength contents [23; 29] or pybometrics, agility, and speed contents [24]. Finally, regarding the injury surveillance, most of the analyzed studies observed a decrease in the rate of injuries [22; 29; 30; 32]. Exclusively, one study [30] did not report significant results, probably considering the low compliance of the training program.