## 4 Discussion
### Location and Type of Injuries  
The results suggest the thigh as the most commonly injured body area, with hamstrings being slightly more injured than the quadriceps muscle. In accordance with our results, the upper leg (i.e., anterior and posterior thigh) has been considered to be the most common injury location in youth football players [9; 29; 30]. Generally, previous epidemiologic studies in adult football players have shown that the hamstring group is the single most injured muscle [12; 31]. It is important to highlight the architectural specifics of the muscle, as the hamstrings are a multi-joint muscle group with dual innervation and a great proportion of fast-twitch fibers [32]. These anatomic characteristics can, in some cases, result in a disruption of running coordination patterns and increase injury risk, as it is known that hamstring injuries mostly occur during running, especially at higher velocities [33; 34]. The injury to the hamstrings typically happens during the active lengthening of the muscle (i.e., eccentric muscle contraction), with the late swing phase of the running gate cycle responsible for 81% of strains [35]. With almost the same injury occurrence as hamstrings, the quadricep muscle also seems to be a vulnerable area and is sometimes regarded as the most injured muscle in the youth population [36]. For example, [PERSON] et al. recently reported that previous quadricep injuries, recent hamstring injury, the dominant kicking leg, and competitive match play were all strongly associated with quadricep injuries [37]. Regarding the quadriceps injury mechanism, the kicking action is identified as the most common, due to a high volume of passing and shooting, with quadriceps being the main agonist in these movements [17]. Further, adductor muscles are also common injury sites in football, with highly intense and repetitive movements such as kicking, change in direction, and inside passing [38]. The hip-groin-pelvis region is highly affected in the PHY period when muscles and tendons adapt slowly to changes in limb length and body mass and have, therefore, reduced capacity for producing and sustaining force [39; 40]. It is interesting to note that 87% of all muscle injuries included four big muscle groups in the lower limb. Comparably, [PERSON] et al. reported that 92% of all muscle injuries affect the hamstrings, quadriceps, adductors, and calves in professional footballers [11].  
A considerably higher number of DOMS injuries was noticed, in contrast to muscle ruptures (88 vs. 42, respectively). Moderate severity (i.e., injury lasting shorter than 28 days) was observed for both types of injuries, with DOMS resulting in 7.5 days lost from training, compared to 25.8 days of time loss due to muscle rupture. As previously mentioned, this result is not surprising because, unlike ruptures, DOMS is not characterized by structural fiber damage. Similarly, a 4-year prospective study revealed a median of 4.2 and 22.5 days of time loss, for DOMS and muscle tears, respectively [41]. The re-injury rate was the same for DOMS and muscle ruptures, with every fifth injury being a re-injury. The same is reported in a study by [PERSON] et al., where 22% of injuries are relapses of a previous injury [42]. Such a high re-injury rate may be explained by a premature attempt to return to unrestricted activity, with the injured tissue not being fully reorganized and healed [36].