## 4 Discussion
### Injury Incidence  
The results of this study have shown a slightly higher overall injury incidence compared to the recent meta-analysis on a similar sample (i.e., U13-U16 players) (7.02/1000 h vs. 5.3/1000 h, respectively) [1]. However, when compared to the Swedish players of the same age, our players displayed almost the same injury rates (7.02/1000 h vs. 6.8/1000 h) [20]. More specifically, the mean muscle injury incidence in our study is found to be 2.73/1000 h. Similarly, investigators reported a muscle injury rate of 3.2/1000 h in a group of U13-U18  
Figure 4: Proportion of players with muscle injuries.  
Figure 3: Proportion of muscle injuries.  
Middle Eastern football players [21]. Interestingly, the number of muscle injuries remains quite stable throughout the six competitive seasons, as there is no significant difference between the years, which is reflected in the IRR of 1.01 between year one and year six. Regarding the injury time trends, a major 18-year prospective cohort study revealed a gradual decrease in training and match injury rates of professional football players [22]. However, as far as muscle injury trends are concerned, the situation is quite the opposite. For example, the number and severity of hamstring injuries doubled in the last 21 seasons, with muscle injuries increasing by 6.7% annually over the last 8 seasons [12]. This increment is explained through a continuous increase in both intensity (i.e., higher volume of running at higher velocities) and total amount of international team travel and matches.  
Although minimal, an evident annual decrease in injuries was present up until the 2019/20 season, from which the number of injuries rose again. This trend change coincides with the emergence of the COVID-19 pandemic. The pre-pandemic injury drop can be explained by the current use of scientifically proven training methodologies that have been shown to reduce the risk of injury [23]. These include better preventive measures, more developed training methods and player and coach education, all of which were being applied in the here-stated academy. Since the start of the global pandemic, there has been a lack of studies as there are only a few of them that have examined the effect of the COVID-19 disease on injury occurrence in football, and especially in youth players [24; 25]. The interruption-related training maladaptation, lack of medical evaluation, inadequate re-training period, congested competition schedule, and the negative effect of the disease itself are all associated with the rise in injuries following the comeback to sport [26].  
In line with the existing data, a much higher match than training incidence was observed in this study (7.38/1000 h vs. 2.25/1000 h, respectively). For example, a 10-year study on the elite French U13-U16 football players revealed an injury incidence of 11.2/1000 h and 3.8/1000 h, for match and training, respectively [27]. Among other factors, underlying explanations include greater playing demands and intensities in competition, number of contacts and collisions, and fatigue accumulation during the match [9; 21; 28]. Also, match-induced psychological arousal, observed mainly through higher competitiveness and more aggressive play, results in elevated injury risk [23].