## 1 Introduction  
Despite an increase in the participation of younger generations in sports and physical activities (PAs), a lack of knowledge regarding sports injuries is still an issue [1], and although several influencing factors are already described in the literature [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19], as presented in Table 1, there are still many limitations and inconsistent data concerning variables such as maturation and physical activity intensity [5, 6, 17, 19, 20]. Increased sports involvement from an early age through the years of growth raises serious concerns [1, 17, 19, 20, 21, 22, 23]. Currently, there is a general trend towards specialization, intensive training and competition in early to middle childhood. These factors, combined with a growing body, can predispose young children to sports injuries that may result in long-term dysfunction [17, 5, 6, 17, 18, 19, 20, 22, 24, 25, 26]. Intensity in youth sports not only sacrifices fun but also produces injuries, burnout, social isolation and dropouts and may lead to reduced motor skill development [1, 14, 21, 24]. If the cycle of sports specialization occurs too early in youth, motor skills and neuromuscular development are impaired, which, in turn, increases the risk of injury and potentially reduces opportunities for the child to achieve optimal sport performance [10, 13, 22, 27]. Clear guidelines set by multiple health organizations, designed to reduce injury rates, state that intensive training in children has no physiological or educational justification and claim that diversity of movement and all-around physical conditioning should take priority over specialization. They also advise that specialization in a single sport before adolescence should be discouraged. Moreover, age-appropriate levels of competition should be respected [10; 24]. Likewise, several studies have found an association between injuries and a higher intensity and volume of training, a higher competition level, long training sessions that require repetitive movements, over-scheduling and overtraining [7; 10; 14; 21; 24; 28]. Recent studies have pointed out an increase in sports participation, load and/or intensity prior to injury [7; 29]. These injuries may also be linked to the unique and vulnerable phase of musculoskeletal, motor and cognitive development in youth. High training intensities overlapping with growth spurts increase the risk of sports injuries [12; 30]. The immature musculoskeletal system undergoes several structural and tissue changes and may become less able to cope with traumatic situations and repetitive biomechanical stress [5; 17; 18; 19; 20; 26; 31; 32; 33]. These changes include the asynchronous development of bone and soft tissue [34]: longitudinal growth leaves the bone temporarily more porous and therefore fragile [33], while soft tissues do not undergo this rapid growth and become progressively tighter [31], increasing the tensile forces over growth plates, cartilage, apophysics, muscle-tendon units and joints [34; 31; 33; 24; 35]. Likewise, muscles do not reach their full size until 6 to 12 months after the peak height velocity (PHV), implying a decrease in strength during this stage. In addition, an imbalance between strength and flexibility can occur, as can abnormal movement mechanics [30]. Furthermore, during adolescence, motor control can be affected by changes in balance and coordination, which may have an impact on injury risk [25; 31]. Equally, cognitive maturation at this stage is an important factor to consider. Children and adolescents with poorer concentration may not yet be capable of participating in very demanding activities [35]. Despite a heightened awareness of sports injuries, their risk factors and their complex interactions, the available evidence is still limited and inconclusive, particularly with respect to reliable data about predictors such as biological age and PA intensity [24; 36].