The adolescent growth spurt is believed to be associated with increased risk of acute sport-related injury [11]. Some studies of SRE injuries indicate increased occurrence of injury during pubescence [12–14]. However, prospective studies linking individual injury rates with longitudinal growth records are required to confirm these findings. The risk of sport-related overuse injury also increases during the adolescent growth spurt [10, 13, 15]. Overuse or repetitive microtrauma can strain the musculotendinous units which may occur more frequently during growth spurts [16]. For example, 10–14-year-old (expected age of peak growth) non-elite gymnasts are more likely to experience chronic wrist pain than either before or after this period [17]. Similarly, stress fractures and low back pain occur with greater prevalence during the adolescent growth spurt [18, 19]. However, prospective studies are needed to further evaluate this relationship [10]. The adolescent growth spurt also increases the risk of epiphyseal growth plate injury due to decreased physeal strength [20, 21]. Structural changes in growth plate cartilage during pubescence result in a thicker and more fragile epiphyseal plate [22]. In addition, bone mineralization may lag behind bone linear growth during the pubescent growth spurt, rendering the bone temporarily more porous and more subject to injury [11]. This is supported by the finding that peak gains in bone area preceded peak gains in BMD in a longitudinal sample of boys and girls [23]. Studies of the incidence of acute physeal injuries indicate an increased occurrence of fractures during pubescence [11, 24, 25] and a noteworthy association between peak growth and peak fracture rate [11]. In adolescents, peak incidence of distal radius fracture coincides with a decline in size-corrected bone mineral density (BMD) in both boys and girls.

In boys’ sports, it is believed that risk of injury is greater among older boys since they are faster, heavier, and stronger, and they generate more force on contact. Years of playing experience and older age were significant predictors of high school gridiron football injury [26]. Practice and overall injury rates increased with grade level in boys’ gridiron football [27]. In minor hockey, compared to the youngest age group, Atom, the risk of injury increased significantly through Pee Wee [Rate Ratio (RR) = 2.97; 95 % CI:1.63–5.8], Bantam (RR = 3.72; 95 % CI, 2.08–7.14), and Midget (RR = 5.43, 95 % CI, 3.14–10.17) [28]. In contrast, McKay et al. [29] reported that injury rates were significantly higher among bantam vs. midget hockey players [Injury rate ratio (IRR) 1.51; 95 % CI, 1.03–2.22].

In girls’ sports, the findings between age/level of play are also mixed. Emery and colleagues [30] report a significantly higher injury rate among U14 relative to U18 female soccer players [RR = 3.13, CI: 1.14–10.67 (p = 0.01)]. In contrast, the relative risk for injury among USA Gymnastics level 7–9 girls was 1.47 times greater than level 4–6 gymnasts [31]. This difference was even greater (RR = 4.22) for competition, but not for practice (RR = 0.97).

In some sports, there is evidence of an increased risk of certain types of injury with increasing age. Among baseball players aged 9–12 years, there was a significant increase of elbow injuries in the 11–12-year-old age group (OR = 2.82; CI: 1.30–6.10) [32]. Similarly, gridiron football players aged 11–12 years were 2.9 (95 % CI: 1.01–8.12) times more likely to have a concussion than those aged 8–10 years [33]. Head-injured youth soccer players, aged 15–19 years, were almost two times more likely to be admitted to hospital than their younger counterparts (RR = 2.2; 95 % CI: 1.3–3.6) [34].

Injury characteristics may change across age groups. A retrospective chart review on a 5 % random sample of 5- to 17-year-old patients revealed that the 13–17-year age group sustained more anterior cruciate ligament (ACL) injuries, meniscal tears, and spondylolysis, while young children were diagnosed with fractures, including physeal fractures, apophysitis, and osteochondritis dissecans [35]. The proportion of injuries that were fractures was significantly lower for varsity level of competition than for junior varsity, freshman, combined, or other levels [Injury Proportion Ratio (IPR) 0.71;95 % CI, 0.66–0.77] [36].

Deficiencies in balance are believed to be a risk factor for sport injury, especially to the lower extremity (LE) [5, 37]. Components of the Star Excursion Balance Test (SEBT) were significantly predictive of LE injury in male and female high school basketball players (p < 0.05) [38]. High variations of postural sway in high school basketball players corresponded to occurrence of ankle injuries [Odds Ratio (OR) = 1.22, p = 0.01] [39]. The association between a positive single leg balance (SLB) test and future ankle sprains was significant among high school and college athletes involved in football, men’s and women’s soccer, and women’s volleyball [40]. The relative risk for an ankle sprain with a positive SLB was 2.54 (95 % CI, 1.02–6.03) in this study. Male and female high school basketball players who demonstrated poor balance had nearly seven times as many ankle sprains as subjects who had good balance [41].

In contrast, balance, as measured on a balance board, was not a significant indicator for noncontact ankle sprains in a sample (n = 169) of high school athletes [42]. Similarly, Frisch et al. [43] applied an extensive pre-season test battery, including static and dynamic balance, on a group of U15–U19 football players to determine their relation with risk for injury in general, and for noncontact acute and progressive injuries in particular. Of the variables tested, only physical fatigue was significantly associated with injury (p < 0.05).

Children of the same chronological age may vary considerably in biological maturity, including growth and athletic performance [44]. Unbalanced competition between early- and late-maturing boys in contact sports such as gridiron football, soccer, and ice hockey may contribute to some of the serious injuries in these sports. Unfortunately, data regarding the relationship between maturity and injury in team sports are limited. The nature of this relationship may vary across gender and sport given the specific somatic and maturational demands of sports.

Injured junior high school football players were lighter and slightly less mature (composite of testicular volume, pubic hair, and axillary hair) than noninjured teammates [45]. A study of the relation between biological maturity, as estimated from grip strength and height, and injury among male soccer players aged 6–17 years found a significantly higher proportion of injuries among the tall/weak boys compared with the immature (short/weak), and mature (tall/strong) boys (p < .05) [46].

More physically mature (Tanner stages 3–5) junior high gridiron football players had significantly more injuries than less physically mature (Tanner stages 1, 2) players (p = 0.03) [47]. Similarly, Tanner stage 4/5 was a significant predictor of sport injury among adolescents, ages 10–19 years (OR = 1.3; 95 % CI, 1.2–1.4, p = 0.05) [48]. Unfortunately, individual variation in exposure to risk of injury was not accounted for in this research. Malina et al. [27] estimated injury rates and relative risks of injury during practice and games by grade over two seasons among youth gridiron football players, aged 9–14 years. Age, height, and estimated maturity status (current height as a percentage of predicted mature height) were not related to injury risk.

A nonsignificant higher injury incidence was found in early and normal maturing soccer players compared with later maturing players (as determined by skeletal age) [49]. In contrast, the late maturing players incurred a significantly higher incidence of major injuries compared with early maturing players (p = 0.039). However, early maturing players sustained the highest incidence of groin strains and re-injuries. In contrast, older, taller, and more mature adolescent soccer players had a significantly lower incidence of chronic pain playing on artificial turf [50].

There is conflicting evidence regarding body size and injury risk. A concern, particularly in sports where grouping for competition is by age or grade level, is mismatch between smaller and larger boys. In ice hockey, for example, the average weight and height differences between small and large Pee Wee hockey players were 37.2 kg and 31.5 cm, respectively [51]. Injured fourth and fifth grade gridiron football players were significantly lighter in weight and had lower BMI than their noninjured peers (p = <0.05) [27].

Several studies report an increased rate of injury among heavier gridiron football players [52–54] or football players with a high BMI [54]. Heavier weight produces greater forces which are absorbed through soft-tissue and joints, perhaps increasing injury risk. Increased risk of injury would seem especially true for overweight football players, or among “oversized” athletes in sports like gymnastics [55, 56] and cheerleading [57] where a small body size is related to success in the sport.

Richmond et al. [58] reported a 34 % increased risk for all sports injuries in obese adolescents over 1 year, as determined by BMI, compared to healthy adolescents [OR = 1.34; 95 % CI: 1.02–1.80)]. In contrast, a curvilinear relationship between BMI and sport injury was reported among a random sample of high school students [59]. The lowest risk of injury was observed in adolescents with a BMI >90th percentile, after controlling for other factors. Students with BMI in the 50th–90th percentiles had the greatest risk of sport injury. A relation between body size and specific injury types has also been reported. Nine-12 year-old baseball players taller than 150 cm had a significantly higher risk of elbow injuries (OR = 2.02; CI: 1.07–3.82) [32]. Similarly, among male and female soccer players 13 years and older, taller players (180–189 cm: IRR = 1.32; 95 % CI: 1.06–1.63) had an increased risk of match injury [60]. Being overweight, as indicated by BMI, and an increased risk of ankle sprains was reported in high school athletes [42] and gridiron football players (p < 0.05) [61]. Higher BMI significantly increased the risk of medial tibial stress syndrome in high school female runners (OR = 0.51; 95 % CI: 0.31–0.86) [62]. In contrast, low BMI (<19) was an independent risk factor for stress fractures in a study of female competitive high school runners (p < 0.05) [63].

Most studies examining flexibility did not find an association between flexibility and injury in child and adolescent sport [6]. However, less-flexible female gymnasts were more likely to be injured, although this was not significant at all age and competitive levels [64]. In high school wrestlers, increased shoulder ligament laxity was related to increased risk of shoulder injury (p < 0.05) [65]. However, this finding did not account for differential exposure to risk of injury.

An explanation for the increased risk of overuse injury during the growth spurt was increased muscle-tendon tightness and accompanying loss of flexibility during the growth spurt [15]. However, the results of several studies have not supported this concept [66–68].

Studies of injury in gender-comparable sports indicate a variable risk of overall and specific injury types among males and females. For example, in a study of community-level soccer players aged ≥13 years, injury incidence rates were significantly higher for females (95 % CI: 54.9–74.3) than males (95 % CI: 43.0–51.1) [69]. In contrast, boys had a higher injury rate than did girls (RR = 1.33; 95 % CI: 0.99–1.79) in a 3-year study of high school athletes [70].

Among U.S. high school athletes rare injuries and conditions occurred at a higher rate in boys (12.4 injuries per 100,000 AEs) than in girls (2.51) (RR = 4.93; 95 % CI: 3.39–7.18) [71]. Boys also incurred a greater proportion of shoulder injuries (11.1 %) than girls (1.6 %) (IPR, 6.86;95 % CI3.31–14.43; p < 0.001) in high school sports during 2005–2010 [72]. Among high school cross-country runners, girls had significantly higher injury rates than boys for overall injuries, initial injuries, subsequent injuries for shin, hip, and foot injuries, and for re-injury rates for knee, calf, and foot injuries [73].

During 2008–2010 high school girls had a higher concussion rate (1.7 per 10,000 AEs) than boys (1.0 per 10,000 AEs) (RR = 1.7; CI, 1.4–2.0) in gender-comparable U.S. high school sports [74]. The incidence of concussion was higher for girls than for boys for basketball and track but not for soccer and baseball/softball in the North Carolina High School Athletic Injury Study (NCHSAIS) [57].

In the NCHSAIS [75], the overall rate of knee injuries for boys was 39.2 injuries per 100,000 AEs compared to 24.9 for girls. Although boys had a higher overall rate of knee injuries in US high schools during the 2005–2007 seasons, girls were twice as likely to sustain knee injuries requiring surgery than boys (IPR = 1.98; CI, 1.45–2.70) and twice as likely to incur noncontact surgical injuries (IPR 1.98, CI: 1.23–3.19) [76]. ACL injuries have also been extensively studied in female athletes and there is consensus that they have a higher risk than male athletes [77].

Possible explanations for the difference between genders include hormonal differences, increased joint laxity in female athletes, anatomical differences, and differences in motor control of knee function which may predispose adolescent females to knee injuries in cutting and jumping sports [78]. Furthermore, adolescent growth in females is associated with increases in knee extension strength and decreases in hip abduction and hamstrings-quadriceps ratio strength which have been linked to increased risk for ACL injury and patella-femoral syndrome [79]. Pubertal females had an increased change in abnormal landing mechanics over time, thus predisposing to knee injury [80].

A history of amenorrhea, especially in sports that emphasize leanness, is a risk factor for bone stress injury in physically mature females [10]. However, data regarding menstrual irregularity, low-energy availability, and injury in younger adolescents are rare. Late menarche (age menarche ≥15 years) was an independent risk factor for stress fracture among high school female runners [63]. A survey of high school female athletes on disordered eating (DE) and musculoskeletal injury found that athletes reporting DE were twice as likely to report injury compared to those reporting normal eating behaviors [OR =2.3; 95 % CI: 1.4, 4.0; p < 0.05) [81]. In a study of female athletes competing in eight interscholastic sports, athletes who scored ≥4.0 on the Eating Disorder Examination Questionnaire had a history of oligo/amenorrhea during the past year, and those who had a low BMD (BMD Z-score of -2SD or less) had a significantly greater occurrence of musculoskeletal injury (p < 0.05) [82].

Previous injury is a well-known risk factor for new injury at the same location [26, 30, 63, 73, 83]. Previous musculoskeletal injuries can lead to fibrosis, with adhesions and limited joint motion and function, thus predisposing to further injury at the same site [73]. Restricted joint motion will lead to muscle atrophy and increased compensatory stress on other areas, thus predisposing to injury at other sites. Injury at other sites has also surfaced as a risk factor for new injury [83].

Life stress has been shown to predict injury [84, 85]. In youth sports, this link has been demonstrated in gymnastics [86, 87], soccer [88], and ice hockey [89]. The retrospective nature of injury data collection in some studies and the relatively short periods of monitoring injury and psychosocial variables may influence these findings. However, Steffen et al. [88] reported that high life stress (p = 0.003) and perception of a mastery climate (p = 0.03) (personal accomplishment is emphasized) were significant risk factors for new injuries in female youth soccer players. McKay et al. [29] reported that athletic identity scores below the 25th percentile (as measured by the AIMS) were associated with subsequent injury [IRR = 2.28; 95 % CI, 1.01–1.64)]. However, state anxiety was not a significant predictor of injury in this study of elite youth ice hockey players.

Although multiple coaching education programs are available there are no mandated national coaching education programs in the United States [90]. Additionally, requirements for high school coaches vary from state to state, with some requiring first aid and cardiopulmonary resuscitation (CPR) certification. Numerous coaching education programs provide information related to proper biomechanics of sporting skills, nutrition, physical conditioning, development of athletes, and prevention, recognition, and management of injuries. Unfortunately, many youth sports coaches, although well-meaning parents or teachers, have little professional training or certification related to the sport(s) they coach. This situation has raised concern regarding increased risk of injury in the absence of well-trained coaches.

The National Center for Catastrophic Sport Injury (NCCSI) reports that more than one-half (63.3 %) of direct catastrophic injuries to female athletes arise from high school and college cheerleading [91]. The NCCSI suggests that inexperienced and untrained coaches who try to teach stunts that they neither have the knowledge nor ability to teach, or that are above the skill and capabilities of the team, may increase the risk of catastrophic injury.

Among high school football players, injury rate was not associated with coach skill level [70]. However, if injured, having a coach with more experience, qualifications, and training was associated with reduced odds of severe injury [OR = 0.49; 95 % CI, 0.27–0.92].

In a 3-year study of cheerleading injuries testing a coaching experience/qualification/training (EQT) variable, supervision by coaches with higher EQT reduced injury risk by 50 % (RR = 0.5; CI, 0.3–0.9) and supervision by coaches with medium coach EQT reduced injury risk by nearly 40 % (RR = 0.61;95 % CI, 0.32–1.160 [57]. In contrast, Knowles et al. [70] tested a similar coach EQT across 12 sports and found it not to be a predictor of injury rates when subjected to multivariate analysis.

There is growing concern regarding the contribution of overscheduling (e.g., practices, games, and matches) in youth sports to fatigue overuse injuries [16]. An overscheduling injury may be defined as an injury related to excessive planned physical activity without adequate time for rest or recovery [10]. Studies in a variety of sports such as baseball, tennis, cricket, running, and soccer have demonstrated that high workloads between hours and bouts of activity are consistently associated with increased injury risk [10]. For example, athlete or parent perception of excessive playing/training time without adequate rest in the days before an injury was related to frequency of overuse (p = 0.16) and fatigue-related (p = 0.01) injuries [92]. Only physical fatigue was significantly associated with injury in youth football (U15–U19) [43].

In a case-control study comparing adolescent pitchers who had shoulder or elbow surgery (n = 95) with pitchers with no significant pitching-related injury (n = 45), the factors with the strongest associations with injury were overuse and fatigue [93]. Arm fatigue during the game pitched was a predictor (p < 0.01) of elbow pain in a longitudinal study of elbow and shoulder pain in youth baseball pitchers [94]. Fatigue also appears to play a role in Junior ice hockey, where most injuries occurred during the middle and later portions of the period. Also, most injuries were sustained during the third period of the game [95].