## 4 Discussion
[5], who reported that the greatest time-loss injuries occur in the U14 and U15 age groups, with greater severity of injury occurring in U16s. A plausible explanation for this could be that U16 players are likely to have just had a period of rapid growth in which they may be muscle-skeletally immature, increasing potential severity and time-loss per injury [33]. Thus, strength-training programs, due to their protective effect on injury severity [34], could be a potential preventive strategy with young male soccer players, focusing around the U16 age group. In addition, these programs likely need to start pre-puberty to build training age and technical competency in young soccer players. Considering that soccer involves demanding activity in terms of short-term high-intensity actions (in particular, accelerations and decelerations, as well as rapid changes in direction), it is perhaps unsurprising that lower limbs present the highest number of muscle injuries in our study, which agrees with the previous literature on youth soccer players [5; 10; 11]. As values in previous research reach values near to 96%, this is a major concern in young soccer players, especially taken in parallel with a developing and incomplete muscular/neuromuscular system [9]. In the current study, muscle tears were the main type of muscle injuries, with hamstring (30.44%) and adductor (23.67%) muscle groups presenting the highest incidence rates. Heightened incidences in the adductor muscles were observed in the U14 age group, which could be attributed to the rapid increases in leg length that players experience in this period, which coincides with the peak growth spurt [5]. Finally, 9.2% of muscle injuries were reported as re-injuries, a lower value in comparison to international soccer players [11]. These differences might be explained by a premature return to play of professional soccer players [35] in order to increase team performance, without respecting the biological repair of muscle tissue, indicative of a poor rehabilitation process [16]. In addition, a higher training load in professional players in comparison with young players could explain these differences in the re-injuries rates. Due to its specific characteristics (i.e., multi-joint muscle group with a great proportion of fast-twitch fibers), the hamstrings are the muscle group with the highest injury incidence in both senior [11] and young [19] elite male soccer players. In our study, an incidence of 0.53 hamstring injuries/1000 h were observed. This value is more than twofold in comparison with the injury incidences reported in a previous scientific investigation with adolescent elite soccer players (0.18 hamstring injuries/1000 h) [36]. [PERSON] et al. [36] reported a lower age of participants (i.e., 13-16 years), and younger players reach lower speed peaks during soccer practice [37]; thus, it seems that, since sprinting is shown as the primary mechanism of hamstring injuries in soccer players, this could explain these differences. Regarding this, it is important to prepare soccer players (from the U14 age group) to achieve maximum speeds during match play but also to develop both accelerative and deceleration abilities. Most of the hamstring injuries recorded in our study were categorized as muscle tears, followed by muscle strains. These results differ from those presented by [PERSON] et al. [25] in adult professional English soccer players. Differences might partially be explained by the fact that professional players are able to self-pace when they perceive that an injury might occur; thus, preventing muscle strains that may result in muscle tears [38]. Our data indicate that the biceps femoris is the most-injured muscle of the hamstring complex, which is in agreement with previous research [25]. The anatomy of the biceps femoris (i.e., two different heads with dual innervation [39]) could explain its great injury incidence, since this dual innervation is important during the running cycle, requiring complex neuromuscular coordination patterns [40].