Although longitudinal data are needed to validate the design of existing pathways of either talent or athletic development, it is generally considered more beneficial to have a progressive system in situ rather than have no structure at all. However, although long-term athletic development programs continue to evolve, a number of contraindicating factors associated with modern-day lifestyles of youth are becoming an increasing cause for concern. Enhancing practitioner's knowledge and understanding of how exercise prescription for youth should align with training age, technical competency, growth, maturation, and development is crucial to the progression of our field (59). However, without addressing current issues facing the development of today's youth, practitioners will likely be working in a compromised environment. Specifically, this article will examine how long-term athletic development programs are negatively impacted by (1) inactive lifestyles of youth, (2) the prevalence of obese and overweight youth, (3) early sport specialization and associated injury risk, (4) high workloads of young athletes, and (5) the limitations of existing education curricula.
For the purposes of this commentary, the terms youth and young athletes represent both children (generally up to the age of 11 years in girls and 13 years in boys) and adolescents (typically including girls aged 12–18 years and boys aged 14–18 years). The term athletic development refers to the physical development of youth that encompasses the training of health-, skill-, and performance-related components of fitness. The age-related integration of these components over time is designed to enhance performance, reduce injury risk, and enhance the confidence and competence of all youth. Practitioner denotes an individual responsible for the athletic development of youth and includes: youth sport coaches, sports administrators, strength and conditioning coaches, physical education teachers, athletic trainers, physiotherapists, and other health care providers. Resistance training refers to a specialized method of conditioning, whereby an individual is working against a wide range of resistive loads to enhance health, fitness, and performance (57). Forms of resistance training include the use of body weight, weight machines, free weights (barbells and dumbbells), elastic bands, and medicine balls. The term physical literacy refers to the ability of an individual to use cognitive processes such as anticipation, memory, and decision-making to help move with poise, economy, and confidence in a range of physically demanding environments (130). Fundamental movement skills represent locomotive (running, skipping, and hopping), manipulative (catching, throwing, grasping, and striking), and stabilization (balance, rotation, and antirotation, and bracing) skills (64).
Problem 1: Physical Inactivity
It can be observed from longitudinal data that fitness levels of youth in general have deteriorated over the past 20–30 years (77,107,124). Recent evidence now indicates that a large proportion of children and adolescents routinely fail to accumulate recommended physical activity guidelines proposed by leading health authorities (36,42). Of particular concern, researchers have shown that physical activity levels appear to peak at approximately 6 years of age, after which there is a consistent decline into adolescence and adulthood (125). Additionally, increases in the amount of time viewing television or playing video games (11), reductions or the removal of time devoted to recess (2), reduced time during the school day for physical education (93), reductions in the number of youth who use active transportation to school (107), poor dietary behaviors (14,21,108), and insufficient levels of sleep (37,69,119) are some other lifestyle factors that contribute to reductions in daily physical activity among youth (86). Failure to address negative trends in lifestyle factors such as insufficient sleep or poor dietary behaviors in youth will undoubtedly reduce or blunt the beneficial effects of exercise and potentially increase the risk of sport-related injury. Additionally, researchers have shown that participating in moderate-to-vigorous physical activity (MVPA) is positively associated with emotional state in adolescents (114). Combined, these factors will limit, delay, or postpone athletic development irrespective of the innate talent of the young athlete. Recognizing that daily physical activity early in life is a critical component of all long-term athletic development models, it is imperative that practitioners responsible for the health and well-being of youth are cognizant of the importance of these contributing lifestyle factors and progressively use targeted programming with appropriate interventions.
Cohen et al. (18) indicated that there has been a recent and sustained decline in the muscular strength levels of children within the United Kingdom, reporting a 26% decline in arm strength and a 7% drop in handgrip strength between 1998 and 2008. Additionally, 1 in 10 children could not support their own body weight on a wall bar (18). The authors suggested that the decline in strength levels was likely because of reductions in physical activity levels. Data from other countries shows a similar trend of strength deficits in youth, highlighting declines in both handgrip strength and bent-arm hang performance in Spanish adolescents (77) and a decline in the neuromotor fitness of prepubescent Dutch children (107). Cumulatively, these data indicate that modern-day youth do not possess sufficient levels of muscular strength largely due to physical inactivity. This is an issue that requires immediate attention.
The increased prevalence of deconditioned youth is likely to have a direct impact on the current requirements and future structuring of long-term athletic development programs. Youth require coordinated muscular strength for the successful performance of fundamental movement skills (28,67). It is also established that fundamental movement skill competency is associated with long-term engagement in physical activity (63). Therefore, given the recent decline in both of these fitness parameters, any long-term strategy should prioritize the development of muscle strength and motor skill proficiency during the primary school years. It is imperative that youth engage in training modalities to develop muscular strength and fundamental movement skills in early childhood to maximize their modifiable neuromuscular systems (28,91). These evidence-based guidelines challenge previous athletic development models (8) and counter preconceived concerns surrounding structured resistance training for children.
Potential Solutions to the Problem
Considering the existing levels of inactive youth (36,42) and that childhood inactivity typically leads to sedentary lifestyle behaviors in adolescence and early adulthood (20,99,120,122), it is imperative that youth engage regularly in strength-building and skill-enhancing activities at an early age. Researchers have previously stated that because of the neural plasticity associated with preadolescence, early engagement in integrative neuromuscular training (INT) (which comprises of both health- and skill-related components of fitness) is instrumental in developing long-lasting fundamental movement competency and enhanced physical, psychological, and social development (83). Although it is difficult to identify a definitive age at which to start formalized training, most 7 and 8 year olds are ready for some type of structured training as part of fitness recreation, sports practice, or physical education (31,91). However, younger children (<7 years of age) should still be encouraged to engage with less formalized structured and unstructured activities (e.g., introductory gymnastics and playground activities that promote kinesthetic development and physical literacy). Of note, authors of the 2014 international consensus statement on youth resistance training stated that the child should be emotionally mature enough to accept and follow instructions and possess competent levels of balance and postural control (57).
Despite global physical activity guidelines recommending youth accumulate 60 minutes of MVPA per day (131), details outlining what should comprise 60 minutes of MVPA are somewhat general. The WHO (131) suggested that daily physical activity guidelines for 5–17 year olds should comprise mainly aerobic exercise; with higher intensity training that “strengthens muscle and bone” being performed 3 times per week. Although these guidelines offer support for youth to engage with physical training, it is noteworthy that a greater emphasis is placed on aerobic exercise in comparison with exercise that promotes “muscle and bone strengthening” or skill-building activities. Conversely, practitioners should acknowledge that developing fundamental movement skills and muscular fitness within a well-rounded training program should be the priority for youth, as these physical qualities ultimately provide the foundations for MVPA and help to enhance performance and reduce sport- and physical activity-related injuries. This contention is reinforced by research that shows children with high aerobic fitness and low muscle strength are at a significantly greater risk of skeletal fracture than youth with higher levels of muscle strength and lower aerobic fitness (17). Additionally, a recent position statement from the American Medical Society for Sports Medicine highlighted that a wealth of research now exists that shows neuromuscular training can reduce injury risk, especially injuries to the lower limb (27). Clinical researchers have indicated that the risk of overuse injury can be reduced in youth populations if children and adolescents engage with appropriately prescribed and well-supervised training programs (75,113). Furthermore, it is purported that training programs inclusive of resistance training that target risk factors associated with injury risk (e.g., muscle imbalances) have the potential to reduce overuse injuries by as much as 50% in youth (75,127).
Table 1 summarizes the recommended solutions to reduce the negative impact of physical inactivity on the success of long-term athletic development programs.
Problem 2: Prevalence of Overweight and Obese Youth
The concept of “underuse” injuries suggests that inactivity and a lack of preparatory conditioning is a likely risk factor for the etiology of a number of sports- and physical activity-related injuries (117). In comparison with normal weight youth, data show that overweight and obese children and adolescents are twice as likely to experience an injury when participating in sports or general physical activity (72). Consequently, it is suggested that overweight and obese youth are ill-prepared for the physical demands of sports (57), ultimately placing them at an increased risk of injury (105). Specifically, low fatigue resistance, lack of postural and neuromuscular control, inadequate strength levels, and reduced motor control development have all been proposed as potential mechanisms that increase injury risk within this population (72). Considering the increased demands of controlling an excessively large body mass in response to the unpredictable and dynamic nature of sporting activities, overweight and obese youth should engage in preparatory training, inclusive of both health- and skill-related fitness components before participating in organized sport. A similar approach should be taken for those youth who are of normal weight but inactive. Of note, normal weight inactive youth may appear ready to engage in sport; however, their musculoskeletal systems are likely to require general preparation to meet the demands of sports practice and competition.
Practitioners and parents alike should recognize that participation in sport practices will not necessarily provide enough of a training stimulus to suitably prepare overweight and obese youth for the loadings encountered within sports. Researchers have shown that engagement in organized sports does not guarantee youth attain recommended daily physical activity guidelines (55), nor enable individual needs to be addressed, such as excess body mass, muscle imbalances, dysfunctional movement patterns, and strength and power deficiencies. Similarly, it has been suggested that the risk of acute traumatic injury (e.g., ankle sprain or anterior cruciate ligament injury) is decreased in overweight and obese individuals who participate in age-appropriate preparatory neuromuscular conditioning activities (57,72). Importantly, this risk is reduced to a greater extent when conditioning activities are introduced to youth at an early age (91). Collectively, the data support the premise that a training philosophy based on targeting muscular strength and fundamental movement skills within a well-rounded training program is a suitable approach for obese and overweight youth, much in the same way training prescription is viewed for normal weight children and adolescents (109). Crucially, to maximize their participation in physical activity into adulthood, obese, and overweight youth should be encouraged to adhere to the hallmarks of existing long-term athletic development theory (58) as an ongoing lifestyle commitment.
Potential Solutions to the Problem
Historically, physical activity interventions aimed at preventing or treating overweight and obese youth (especially children) have focused on aerobic exercise (4,109). However, such training modalities can be problematic in terms of compliance and adherence (109). Conversely, training interventions inclusive of motor skill training, strength and power training, and sprint training have all shown relatively high adherence rates in training interventions ranging from 8 to 52 weeks in duration (71,109,111,112). The increased adherence rates associated with neuromuscular training for obese and overweight youth is not surprising given the heightened imposed demands of handling excess body mass for prolonged periods of weight-bearing exercise, in comparison with their normal weight peers. Exposing overweight and obese youth to aerobic exercise (e.g., prolonged periods of running within a physical education class) may actually increase their risk of injury and reduce their self-esteem because of the nature of peer comparison within school-age youth. Researchers have shown that overweight youth experience greater levels of criticism during physical activity (35) and such criticism may limit subsequent engagement in physical activity. Although peer comparison may be a negative process during aerobic exercise, in contrast resistance training offers overweight and obese youth the opportunity to outperform their peers with respect to absolute strength performance. For example, Deforche et al. (24) showed that overweight youth performed better than normal weight youth in activities requiring muscular strength. Although overweight and obese youth carry excess fat mass, they typically possess a large fat-free mass also, thus increasing their potential for absolute strength performance (109). Consequently, overweight and obese youth may be more compliant and enthused to regularly participate in integrative neuromuscular-based training programs.
Irrespective of the potential additive benefits of resistance training programs for overweight and obese youth, practitioners must remain sensitive to the potentially heightened concerns that these populations may have about their increased body mass, especially when overweight and obese youth exercise within the same setting as normal weight youth. Consequently, practitioners will likely need to differentiate activities within training sessions (and overall training programs) to help enable all youth to achieve success irrespective of their body mass. This approach will help foster an approach to exercise that encourages self-improvement and positive social interactions.
Table 2 summarizes key guidelines for practitioners to consider when working with overweight or obese youth.
Problem 3: Early Sport Specialization
Although the injury risks associated with overweight and obese youth arise from insufficient exposure to sports and physical activity (72), of growing concern for children and adolescents are the injury risks associated with excessive exposure to specific sport(s) (27,46). Early sport specialization refers to the engagement in intensive year-round training within a single sport (27) and likely limits the child's exposure to a breadth of sporting activities. It is acknowledged that certain sports traditionally favor early specialization (i.e., gymnastics or figure skating) because of the relative advantage for a young athlete to perform extreme specialized posturing and rotation of the torso and extremities. However, these young athletes should also be engaged with an integrative strength and conditioning program focused to diversify motor skill development and enhance muscle strength to maximize performance and reduce their relative risk of injury. Unfortunately, an increasing number of sports are focusing on exposing children to high levels of formalized sports training at younger ages, even in sports that are typically classified as late specialization sports (e.g., football and rugby) without supportive training to enhance motor skill competency. Researchers have indicated that youth who do specialize early in a sport are at an increased risk of overtraining, overuse injury, and burnout (i.e., stress-induced withdrawal) (1,26,45). Talented youth who are selected for a sporting team during late adolescence but have not engaged in age-appropriate conditioning during their childhood years are more likely to present with poor fundamental movement skills. For example, Iga et al. (48) showed that the muscle-loading patterns associated with youth soccer can lead to alterations in functional hamstrings to quadriceps strength ratios about the knee, and that untrained young soccer players presented with greater quadriceps dominance than those who have participated in formalized resistance training. Recently, researchers have proposed that for those athletes who have specialized in a single sport at an early age, physical training should concentrate on enhancing generic movement skills and addressing muscle weakness or imbalances (59) instead of being exposed to sport-specific performance-driven training. Providing progressive and multifaceted training opportunities for such athletes to develop more fundamental movement skills may overcome the propensity for early specializing athletes to be at increased risk for a sports-related injury, illness, or burnout (45,91).
It is accepted that not all acute injuries are unavoidable in sport; however, practitioners should be cognizant of risk factors that may predispose youth to overuse injuries. Overuse injuries are defined as an injury caused by repetitive submaximal loading of the musculoskeletal system with inadequate recovery time for subsequent adaptation (27,113). It is suggested that the proportion of acute versus overuse injuries in youth is approximately 50:50; however, it is feared that the number of overuse injuries is rising (12). Conditions such as patellofemoral pain (65,86), Osgood–Schlatter disease (41), calcaneal apophysitis (95), little league elbow (52) and little league shoulder (113), spondylolysis (53), and osteochondritis dissecans (100) are all common overuse injuries seen in children and adolescents subject to repetitive sports training. As youth engage earlier in formalized sport and specialize in sport(s) at younger ages, they may be at increased risk of experiencing overuse injury (45). Of concern, researchers have shown that the cycle of reduced activity after an acute injury can initiate overweight and obesity markers in youth (84).
Irrespective of whether long-term modeling is focused on developing talent or athleticism, existing literature is unequivocal that experiencing a range of activities during childhood is an important component of youth development (8,22,40,58). From a talent development perspective, researchers have shown that expert decision-making processes can be enhanced when young athletes are exposed to a breadth and depth of sporting experiences (7). Additionally, it was suggested that exposure to a variety of activities where generic pattern recognition, hand-eye coordination, and decision-making skills can be developed, will ultimately avoid the need for early specialization (7). This is exemplified from the talent development of a young team sport athlete (e.g., soccer player). Although soccer may be the primary sport that the child participates in, they are likely to develop perceptual and decision-making skills such as visual scanning, anticipation, and movement pattern recognition from participating in similar invasion-based sports (e.g., basketball or rugby). Researchers have also shown that a diversification approach to sampling many different sports during childhood is optimal for the development of gross motor coordination (38) and subsequent athletic performance later in life (56,76). Such research refutes the misnomer of the “10,000-hour rule,” which is underpinned by an individual seeking to acquire expertise in a given activity needing to engage in 10,000 hours (or 10 years) of deliberate practice, a theory that has been adopted by previous athletic development models (8). Conversely, the research of Moesch et al. (76) and Fransen et al. (38) shows that accumulating 10,000 hours of specific practice does not guarantee success and may not be needed to reach elite performance levels later in life.
From an athletic development perspective, it is important to expose youth to a variety of movement patterns to ensure that a child can competently perform a breadth of movement skills in a range of different activities and environments before specializing in specific movement patterns within a single sport. Children also need to be introduced to a breadth of activities as a high proportion of youth who specialize early will not successfully reach the highest level of elite sport and will therefore require a requisite level of athleticism to support lifelong participation in recreational sport and physical activity. Specifically, a young athlete should be able to repeatedly produce a range of high quality movement capacities (e.g., pushing, pulling, rotating, bracing, jumping and landing, rolling, twisting, hopping, running, and stabilizing) with requisite force production and attenuation before being exposed to the rigors of repetitious sport-specific training.
Potential Solutions to the Problem
Encouraging youth to participate in a variety of sports during their growing years can help them develop more diverse motor skills. Sports specialization in youth may underlie reduced diversity in motor skill proficiency as young athletes focus on sport-specific skills, while ignoring motor skills developed through a diversified participation portfolio (38). Although speculative, if sports specialization occurs too early in children and if young athletes continue to progress their level of competition, their opportunities for participation in “fun”-focused age-related physical activities are likely to be limited, which further stifles diversity in motor skills and limits current and long-term physical activity and health (79). Consequently, comprehensive motor skill development will be stifled, which can also increase risk of future injury and potentially reduce opportunities to achieve optimal sport performance (45,79).
Children who do participate in specialized sport activities more than 16 hours a week of intense sport-specific focused training should be closely monitored for indicators of burnout, overuse injury, or potential decrements in performance from overtraining. In addition, with the competitive demands typically higher for athletes specialized in a single sport, intrinsic risk factors of acute injury that are higher during competition compared with training should be monitored during accumulated games, matches, meets, or tournaments (47). Specialized athletes involved in intense competition should be allowed sufficient recovery time between repeated bouts of same day (10,49). Before prolonged competitions, athletes can also benefit from limiting intense training 48 hours before competition (66). Continued research is needed to better delineate the threshold competition volume relative to the emergence of risk factors associated with overscheduling to better establish formal guidelines to optimize safe youth sport performance.
Based on the current evidence, we encourage youth to engage in preparatory INT before the initiation of competitive sport participation. Integrative neuromuscular training includes general (e.g., strength-building exercises) and specific (e.g., exercises targeted to address motor control deficits) conditioning activities that are designed to enhance both health- and skill-related related fitness (13,83). In terms of physical conditioning, youth sport practice and games may not enable the young athlete to accumulate the recommended amount of moderate-to-vigorous physical activity, as a large proportion of time in practice (and even competition) can be spent in sedentary or low-intensity physical activities (43,55). A young athlete's participation in sport should evolve out of preparatory conditioning and instructional practice sessions that address individual deficits and prepare their motor systems for the demands of practice and competition (57,80). Properly designed INT implemented in preseason and off-season periods can be especially beneficial to athletes who have specialized in sports and may not have had adequate exposure to developmental motor skill activities (82). Integrative neuromuscular training provides supportive conditioning that can reduce injury risk and enhance performance in all athletes (29,34,87–89).
In athletes, it would seem that success at young ages does not predict long-term success, and in some cases, early sport specialization may limit the potential to achieve elite status. These data provide support to the concept of early sport diversification and recognizes that while deliberate play and practice and formalized sports training is certainly necessary for success in sports, it is not likely sufficient to achieve maximum performance with reduced injury risk without integration of appropriate long-term athletic training programs.
Table 3 summarizes key recommendations to reduce the negative impact of early sport specialization.
Problem 4: Training Workloads of Youth
For the welfare and well-being of youth, long-term athletic development pathways must be administered and monitored carefully by practitioners responsible for the overall development of the child or adolescent. Without regular communication between practitioners, youth may be at risk for excessive training workloads, contraindicating training methods, insufficient rest and recovery, and additional nontraining stressors. Practitioners should also be aware that although children will often recover more quickly than adults from exercise (especially high-intensity exercise) (104) because of their underlying physiology, the effects of accumulated fatigue on neuromuscular control and function after repeated exposure to exercise in youth remains unclear. Combined, these factors can theoretically lead to excessive workload accumulation and youth experiencing nonfunctional overreaching (6), overtraining syndrome (74), or burnout (61).
Data on youth from the United Kingdom have shown that a relatively high proportion of young athletes have reported experiencing overtraining or nonfunctional overreaching (68). Specifically, 29% of 376 young athletes competing at club to international level from 19 different sports reported experiencing overtraining or nonfunctional overreaching at least once (68). Although Matos et al. (68) indicated that overtraining or nonfunctional overreaching were not solely a result of physical training load, it is likely that a long-term development plan that fails to allow sufficient time for recovery, adaptation, and natural growth processes will increase the likelihood of negative health outcomes for youth (23). When considering the overall workload of the child or adolescent, it is imperative that practitioners value the quality of practice and competition, as opposed to the quantity of training or competition time.
Researchers have shown that parental or coach-led pressure can positively or negatively influence youth (98). Such external pressure to perform in multiple competitions or to train or play when injured to make selection for higher level competitions (i.e., national team rosters or securing professional contracts) can also contribute to the risk of intolerable workloads. Consequently, balancing exposure between competitive events and time dedicated towards physical preparation must be an integral component of any long-term athletic development model.
Possible Solutions to the Problem
The objective of the strength and conditioning coach is to carefully manipulate training loads to achieve long-term adaptations in physical performance. Although practitioners will intuitively adopt their preferred philosophy of periodization (e.g., progressive cycling of various aspects of training), it is generally accepted that planning sequential blocks of training is crucial to elicit the greatest adaptive response. Recently, Haff (44) suggested that for young children entering a long-term athletic development model, the majority of their time engaged within the system should be devoted to general preparatory training and the development of fundamental movement skills. However, as the child moves through the long-term athletic development pathway, a greater emphasis should be placed on competition, so that by the time they reach adulthood (approximately 20 years of age), they will spend 25–35% of their time in training and 65–75% of their time in competition (44). Although these ratios are estimations and do not account for individual differences, the notion of prioritizing general preparatory training and developmental practices during the early stages of childhood is essential. Such an approach will hopefully avoid excessive competitive workloads and negative experiences, which may ultimately lead to premature disengagement from the sport during early adolescence (97). Such an approach should also help ensure the holistic development of youth (96). Interestingly, Matos et al. (68) reported that level of competition was significantly correlated with the incidence of nonfunctional overreaching or overtraining; and therefore, practitioners working with youth must ensure that long-term athletic development is driven by process (athlete-centered) as opposed to outcomes (results-oriented), especially at the younger ages of competition.
The need for a comprehensive approach that is considerate of all demands to long-term athletic development is emphasized for youth who participate in multiple sports. The design of training programs for single-sport athletes will typically include an appropriate phase of physical preparation before the onset of a competitive phase. However, for youth who participate in multiple sports, competitive seasons may run synonymously (i.e., 2 winter sports) or overlap (e.g., a fall, winter, and spring sport). Irrespective of the arrangement of the seasons, practitioners must avoid the temptation of solely focusing on the loading stimulus during training phases and ensure that adequate transition and preparation phases exist within the overall long-term athletic development plan. Enforced transition/preparation phases from sport-specific training are also essential to ensure that the child has sufficient time to rest and recover and to enable normal growth and maturation processes to occur. These phases are also important to safeguard against the negative effects of accumulated fatigue and potential risks of overuse injury. An example of this is apparent in recent recommendations whereby young baseball pitchers are encouraged to pitch for no more than 8 months within a 12-month time frame to reduce the risk of overuse injury in the shoulder (3). General preparation should also be viewed as an opportunity to regain, or improve on, precompetition levels of fitness that would typically have plateaued or decreased as a result of the demands of the competitive season. For example, during an enforced transition/preparation phase, a practitioner may need to rectify muscle imbalances or decrements in motor skill proficiency that have developed through exposure to competition and reduced opportunities for preparatory conditioning. Youth who specialize in a single sport should be encouraged even more to participate in planned periods of enforced preparation to allow exposure to isolated and focused INT, to enhance diverse motor skill development, and reduce injury risk factors. Such an approach requires a high degree of cohesion between practitioners of different sports/teams, which might be challenging. However, for the long-term welfare and well-being of the child or adolescent adequate preparation time must be viewed as a critical component of any athletic development model.
Several prominent international organizations have recommended that the training of youth athletes should be monitored to avoid the negative consequences of excessive training (1,27,81). Whether these recommendations are being implemented is unknown, but the continued reporting of consistent levels of staleness, burnout, and overtraining in youth sports suggest that more needs to be done to protect youth athletes (50,68,103). Part of the problem is the difficulty of identifying initial symptoms of overtraining in youths. Prolonged impairments in performance are a defining characteristic of overtraining in adults (73). In youth growth, maturation and development may obscure the ability to identify decrements in performance caused by overtraining. Performance decrements lasting months or longer may be caused by a naturally occurring period of adolescent awkwardness, as has been noted in youth soccer players (101). Conversely, overtraining may cause impaired responsiveness to training but with natural growth and maturation processes still allowing some level of improvement or maintenance of performance, masking the negative consequences of overtraining. Supporting the difficulty of identifying physical symptoms of overtraining the American Medical Society for Sports Medicine (27) have stated that there seems to be more of a psychological component to burnout and attrition in youth sports.
A holistic approach should be adopted to monitoring youth athletes, considering both physical and psychosocial perspectives. In addition to performance decrements, the most prevalent physical symptoms association with nonfunctional overreaching and overtraining in youth sports include loss of appetite, predisposition to injury, frequent tiredness, inability to cope with training loads, frequent respiratory infections, heavy muscles, and sleep problems (68). Although the most prevalent psychological symptoms include apathy, feeling intimidated by opponents, bad mood, often feeling sad, lack of confidence in the future and in competition (68). Coaches should educate youth athletes and their parents to be aware of such symptoms, build a good rapport with their athletes to help identify potential symptoms, have robust monitoring systems in place to allow early detection of overtraining, and have appropriate strategies to deal with suspected cases of overtraining. As an example of psychological monitoring, the profile of mood state has been widely used to identify overtraining in adult athletes and a condensed, 24-question version, has been validated for use with adolescent populations (123).
Key considerations for practitioners to consider when managing the training workloads of youth are presented in Table 4.
Problem 5: Current Physical Education Provision
During childhood, the neuromuscular system is highly “plastic” (33,91) and is amenable to adaptation owing to the peaking of brain maturation rates (6–8 years and 10–12 years) (102), synaptic pruning (15), and overall strengthening of the synaptic pathways (16). It has also been established that fundamental movement skill mastery and motor proficiency are positively associated with long-term engagement in physical activity (115,116), and that childhood is an opportune time for motor skill development. Research also shows that muscular strength is important for motor skill performance (9,19,32,60,121,126) and that children can make worthwhile improvements in muscular strength after appropriate training interventions (9). Consequently, because of the neural plasticity associated with childhood and the responsiveness to motor skill and resistance training, a strong focus of physical education curricula should be based on developing a breadth and depth of movement skills and requisite levels of muscular strength (58).
Notwithstanding the awareness of substandard levels of current health and fitness of modern-day youth, the lack of robust governmental strategies for physical activity within the education sector remains a critical cause for concern (129). Not all modern physical education curricula exclusively involve the enhancement of physical fitness and have become more diverse in terms of subject content and required learning outcomes. For example, within the United Kingdom, in addition to primary school pupils being taught to play competitive sports, learn dance and rhythmic movement patterns, and participate in outdoor and adventurous activities; they must also be taught to develop critical thinking skills and learn to use information technology within the physical education setting (25). Despite modern-day policies leading to an increased demand on physical education teachers, it should be noted that the term “physical education” represents the educating program related to the physique of the human body and should encourage psychomotor learning in a variety of settings that promote health and exercise (5). Therefore, even with such a broad range of curricula requirements to satisfy, physical education programs must retain a central tenet of offering youth the opportunity to engage in meaningful physical activity that enhances both health and skill-related components of physical fitness. Because childhood represents a unique opportunity to take advantage of a highly plastic neuromuscular system, exposure to daily primary school physical education curricula would seem to be a critical time frame in which to develop athleticism, promote psychosocial development, and instill motivation for lifelong engagement in regular physical activity.
Despite the obvious role for the education sector to teach and develop health and skill-related fitness in school-age youth, researchers have shown that current education systems are failing to develop appropriate standards of fitness (77,107,118). For example, an examination of the national curricula for physical education within the United Kingdom shows that there is minimal reference to age-appropriate motor skill development and resistance training for school children, especially for primary school education. Furthermore, in the United Kingdom, it is recognized that primary school teachers are poorly prepared through their teacher training programs to teach physical education (51), and it has been suggested that the statutory requirements for physical education have often not been achieved (51). It would seem that limited subject knowledge is often the primary explanation for inadequate standards of physical education teaching in primary schools within the United Kingdom (94).
Similar negative trends are evident within the United States, with more than half of all states permitting school districts to allow students to substitute other activities for their required physical education classes (92), and 59% of states allowing required physical education credits to be earned through online computer-based courses (93). The inability of existing education curricula to appropriately prepare children for the demands of recreational fitness or sporting activities was reflected in recent data examining the preparedness of college freshmen for the rigors of college-based strength and conditioning (128). The researchers showed that current college strength and conditioning coaches believed the areas of athleticism requiring the greatest improvement of college freshmen were lower extremity strength, weightlifting technique, core strength, and overall flexibility (128). It is reasonable to suggest that if education sectors possess more highly skilled practitioners in the provision of athletic development, the number of youth entering college-based programs with substandard levels of athleticism could be reduced.
Irrespective of the existing concerns with the provision of physical education curricula, a recognized and certified continued professional development (CPD) pathway does not currently exist for practitioners to enhance their knowledge base and practical skill sets within the field of youth athletic development. Furthermore, it is likely that a number of physical education teachers working within schools (especially primary schools) may not be willing or motivated to actively participate in continued CPD opportunities related to long-term athletic development, which poses a very real problem if existing education curricula are to change to address the current syllabus that is delivered to school-age youth. For example, recently, it has been shown that high school physical education teachers' and youth sport coaches' knowledge and understanding of youth resistance training is deficient and not consistent with the recommended guidelines (39,70). Consequently, it is imperative that physical education teacher training programs provide trainee teachers with the relevant curriculum to ensure that, at least, newly qualified teachers possess up-to-date knowledge and the necessary skill sets to deliver appropriate athletic development curricula to all youth.
Possible Solutions to the Problem
Cumulatively, it would seem that the content of existing education curricula and the knowledge of practitioners responsible for the delivery of such curricula are suboptimal for long-term physical development in youth. Despite the short- and long-term benefits of appropriately prescribed physical development interventions on the health and fitness of youth (29,54,62), it would seem that existing education structures require a dramatic overhaul to enhance their capacity to reverse the cascading effects of physical inactivity and its associated negative health outcomes (32,129).
Within existing physical education curricula, what could be viewed as “athletic development” is often termed health-related exercise (HRE) and is typically delivered in discrete units of work across a single school term (94), often by practitioners without the relevant expertise in long-term athletic development. These units of work are then replaced with more traditional units of seasonal sports (e.g., rugby, soccer, or hockey). Adopting such a short-term policy will blunt the continual development of athleticism of youth, will likely enable some form of detraining to ensue, and not facilitate the correction of key injury risk factors (e.g., poor landing mechanics or lack of postural stability). Researchers have shown that significant improvements in physical fitness can be achieved from approximately 15 minutes of INT twice weekly (30,29). Therefore, some form of targeted athletic development training should be creatively incorporated into all physical education classes (e.g., dynamic warm-up activities) and not just limited to independent blocks of HRE teaching.
The development of athletic potential in school-age youth should be viewed as a long-term process. To adopt some form of periodization to the school physical education system, practitioners should view the school career of youth as a sequence of multiyear plans: (1) primary school years and (2) years spent in secondary education. By integrating a long-term periodized approach within the school system, practitioners can structure sequential annual curricula to progressively build on the athletic potential of all youth. Within each school year, practitioners can then design each term to serve as a structured mesocycle (typically 4–8 weeks), with each teaching week representing a structured microcycle (5–7 days). Although such an approach may initially seem complex and unrealistic, using this type of periodized approach to school-based physical education should offset the chances of exposing youth to isolated blocks of HRE that fail to produce long-term gains above and beyond that of growth and maturation.
Of interest to the practitioner is how philosophies from athletic development modeling (58) can be integrated within school-based physical education. Initially, practitioners working within a school system should ensure that children are exposed to varied practices that focus on developing a broad range of athletic motor skill competencies (AMSC (78); Figure 1) and appropriate levels of muscle strength. Such an approach is illustrated within the Composite Youth Development (CYD) model presented in part 1 of this commentary. Within the primary education sector, such practice should be delivered and developed through exploratory activities that stimulate creativity in the child, which, in turn, increases enjoyment and motivation. Teachers should avoid relying purely on sport-specific skill development or low-intensity and prolonged aerobic exercise. Additionally, primary physical education should be viewed as an opportunity to teach motor skills that can facilitate more advanced training modes at later stages of development. For example, a teacher should attempt to develop fundamental movement patterns and body weight management ability in young children (e.g., through the use of basic gymnastic type activities) that will act as the foundations for more complex activities (e.g., weightlifting exercises, advanced plyometrics and high velocity, speed, and agility activities). Within the primary school sector where physical education budgets may be limited, practitioners working with youth should realize that expensive equipment is not necessarily required to develop competent motor skill proficiency and primal levels of muscle strength in young children. For example, there are many different forms of resistance that can be used as an overload stimulus to develop muscle strength (e.g., body weight, manual resistance, elastic bands, medicine balls), all of which have proven successful in training interventions in youth (57).
Table 5 provides recommendations for practitioners to consider when working within existing educational systems.
Need for an Internationally Recognized Youth Training Certification
Irrespective of which model is adopted by practitioners, the success of any youth training plan is largely based on the suitability of the program design and the pedagogical skills of the practitioner(s) responsible for its delivery (33,83). Although existing models have undoubtedly furthered the cause of youth training, the depth of understanding of growth and maturation influences on physical performance and how these influence program design remains highly varied among practitioners. Consequently, an internationally recognized youth training certification should be developed and endorsed by professional organizations to help ensure the provision of safe and effective exercise prescriptions for children and adolescents. Importantly, such a certification process would require a practitioner to be assessed for knowledge and understanding of key concepts surrounding pediatric exercise science, the ability to design, coach and modify developmentally appropriate training programs, and pedagogical skills to ensure that scientific principles can be translated into practice in a child-focused approach. Such a certification process should become accepted practice, not just within sporting administrations but also in the education and health care sectors, especially in light of recent trends in MVPA and the increasing prevalence of sport- and physical activity-related injuries in youth. The concept of an internationally recognized certification is particularly important given the existing knowledge and awareness of current guidelines for youth-specific exercise prescription within the sport, education, and health care systems (32,39,110). Irrespective of whether practitioners are working with youth in competitive sports, recreational activity, daily physical education classes or organized health-based interventions, an internationally recognized certification is deemed an important developmental step to ensure that philosophies and practices of long-term athletic development are geared towards ensuring the holistic development of all youth.
1. American Academy of Pediatrics, Committee on Sports Medicine and Fitness. Intensive training and sports specialization in young athletes. Pediatrics 106: 154–157, 2000.
2. American Academy of Pediatrics, Council on School Health. The crucial role of recess in school. Pediatrics 131: 182–188, 2013.
3. American Academy of Pediatrics, Council on Sports Medicine and Fitness. Baseball and softball. Pediatrics 129: e842–e856, 2012.
4. American Academy of Pediatrics, Council on Sports Medicine and Fitness, and Council on School Health. Active healthy living: Prevention of childhood obesity through increased physical activity. Pediatrics 117: 1834–1842, 2006.
5. Anderson D. The Discipline and the profession. In: Foundations of Canadian Physical Education, Recreation, and Sports Studies. Dubuque, IA: Wm. C. Brown Publishers, 1989.
6. Armstrong LE, VanHeest JL. The unknown mechanism of the overtraining syndrome: Clues from depression and psychoneuroimmunology. Sports Med 32: 185–209, 2002.
7. Baker J, Cote J, Abernethy B. Sport specific practice and the development of expert decision-making in team ball sports. J Appl Psychol 15: 12–25, 2003.
8. Balyi I, Hamilton A. Long-Term Athlete Development
: Trainability in Childhood and Adolescence. Windows of Opportunity. Optimal Trainability. Victoria, British Columbia, Canada: National Coaching Institute British Columbia and Advanced Training and Performance Ltd, 2004.
9. Behringer M, vom Heede A, Matthews M, Mester J. Effects of strength training on motor performance skills in children and adolescents: A meta-analysis. Pediatr Exerc Sci 23: 186–206, 2011.
10. Bergeron MF, Laird MD, Marinik EL, Brenner JS, Waller JL. Repeated-bout exercise in the heat in young athletes: Physiological strain and perceptual responses. J Appl Physiol (1985) 106: 476–485, 2009.
11. Braithwaite I, Stewart AW, Hancox RJ, Beasley R, Murphy R, Mitchell EA. The worldwide association between television viewing and obesity in children and adolescents: Cross-sectional study. PLoS One 8: e74263, 1–8, 2013.
12. Brenner JS. Overuse injuries, overtraining, and burnout in child and adolescent athletes. Pediatrics 119: 1242–1245, 2007.
13. Bukowsky M, Faigenbaum AF, Myer GD. Fundamental Integrative Training (FIT) for physical education. J Phys Educ Recr Dance 85: 23–30, 2014.
14. Carlson JA, Crespo NC, Sallis JF, Paterson RE, Elder JP. Dietary-related and physical activity-related predictors of obesity in children: A 2-year prospective study. Child Obes 8: 110–115, 2012.
15. Casey BJ, Giedd JN, Thomas KM. Structural and functional brain development and its relation to cognitive development. Biol Psychol 54: 241–257, 2000.
16. Casey BJ, Tottenham N, Liston C, Durston S. Imaging the developing brain: What have we learned about cognitive development? Trends Cogn Sci 9: 104–110, 2005.
17. Clark EM, Tobias JH, Murray L, Boreham C. Children with low muscle strength are at an increased risk of fracture with exposure to exercise. J Musculoskelet Neuronal Interact 11: 196–202, 2011.
18. Cohen DD, Voss C, Taylor MJD, Delextrat A, Ogunleye AA, Sandercock G. Ten-year secular changes in muscular fitness in English children. Acta Paediatr 100: e175–e177, 2011.
19. Comfort P, Stewart A, Bloom L, Clarkson B. Relationships between strength, sprint, and jump performance in well-trained youth soccer players. J Strength Cond Res 28: 173–177, 2014.
20. Corder K, Sharp SJ, Atkin AJ, Griffin SJ, Jones AP, Ekelund U, van Sluijs EMF. Change in objectively measured physical activity during the transition to adolescence. Br J Sports Med 2014. doi:10.1136/bjsports-2013-093190. Epub ahead of print.
21. Corder K, van Sluijs EMF, Steele RM, Stephen AM, Dunn V, Bamber D, Goodyer I, Griffin SJ, Ekelund U. Breakfast consumption and physical activity in British adolescents. Br J Nutr 105: 316–321, 2011.
22. Côté J, Baker J, Abernethy B. Practice to play in the development of sport expertise. In: Handbook of Sport Psychology. Eklund R., Tenenbaum G., eds. Hoboken, NJ: Wiley, 2007. pp. 184–202.
23. Curran T, Appleton PR, Hill AP, Hall HK. The mediating role of psychological need satisfaction in relationships between types of passion for sport and athlete burnout. J Sports Sci 31: 597–606, 2013.
24. Deforche B, Lefevre J, Bourdeaudhuij ID, Hills AP, Duquet W, Bouckaert J. Physical fitness and physical activity in obese and nonobese Flemish youth. Obes Res 11: 434–4041, 2003.
25. Department for Education. Physical education programmes of study: Key stages 1 and 2—National curriculum in England. 2013. Available at: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/239040/PRIMARY_national_curriculum_-_Physical_education.pdf
. Accessed February 9, 2014.
26. DiFiori JP. Evaluation of overuse injuries in children and adolescents. Curr Sports Med Rep 9: 372–378, 2010.
27. DiFiori JP, Benjamin HJ, Brenner J, Gregory A, Jayanthi N, Landry G, Luke A. Overuse injuries and burnout in youth sports: A position statement from the American Medical Society for Sports Medicine. Clin J Sport Med 24: 3–20, 2014.
28. Faigenbaum AD, Chu DA, Paterno MV, Myer GD. Responding to exercise-deficit disorded in youth: Integrating wellness care into pediatric physical therapy. Pediatr Phys Ther 25: 2–5, 2013.
29. Faigenbaum AD, Farrell A, Fabiano M, Radler T, Naclerio F, Ratamess NA, Kang J, Myer GD. Effects of integrative neuromuscular training on fitness performance in children. Pediatr Exerc Sci 23: 573–584, 2011.
30. Faigenbaum AD, Farrell AC, Fabiano M, Radler TA, Naclerio F, Ratamess NA, Kang J, Myer GD. Effects of detraining on fitness performance in 7-year-old children. J Strength Cond Res 27: 323–330, 2013.
31. Faigenbaum AD, Kraemer WJ, Blimkie CJ, Jeffreys I, Micheli LJ, Nitka M, Rowland TW. Youth resistance training: Updated position statement paper from the national strength and conditioning association. J Strength Cond Res 23: S60–S79, 2009.
32. Faigenbaum AD, Lloyd RS, Myer GD. Youth resistance training: Past practices, new perspectives and, future directions. Pediatr Exerc Sci 25: 591–604, 2013.
33. Faigenbaum AD, Lloyd RS, Sheehan D, Myer GD. The role of the pediatric exercise specialist in treating exercise deficit disorder in youth. Strength Cond J 35: 34–41, 2013.
34. Faigenbaum AD, Myer GD, Farrell A, Radler T, Fabiano M, Kang J, Ratamess N, Khoury J, Hewett TE. Integrative neuromuscular training and sex-specific fitness performance in 7-year-old children: An exploratory investigation. J Athl Train 49: 145–153, 2014.
35. Faith MS, Leone MA, Ayers TS, Heo M, Pietrobelli A. Weight criticism during physical activity, coping skills, and reported physical activity in children. Pediatrics 110: e23, 2002.
36. Fakhouri THI, Hughes JP, Burt VL, Song MY, Fulton JE, Ogden CL. Physical Activity in U.S. Youth Aged 12-15 Years, 2012. NCHS Data Brief, No. 141. Hyattsville, MD: National Center for Health Statistics, 2014.
37. Foti KE, Eaton DK, Lowry R, McKnight-Ely LR. Sufficient sleep, physical activity, and sedentary behaviors. Am J Prev Med 41: 596–602, 2011.
38. Fransen J, Pion J, Vandendriessche J, Vandorpe B, Vaeyens R, Lenoir M, Philippaerts RM. Differences in physical fitness and gross motor coordination in boys aged 6-12 years specializing in one versus sampling more than one sport. J Sports Sci 30: 379–386, 2012.
39. Fröberg A, Alricsson M, Ahnesjö J. Awareness of current recommendations and guidelines regarding strength training for youth. Int J Adolesc Med Health 26: 517–523, 2014.
40. Gagné F. Constructs and models pertaining to exceptional human abilities. In: International Handbook of Research and Development of Giftedness and Talent. Heller K.A., Monks F.J., Passow A.H., eds. Oxford, United Kingdom: Pergamon Press, 1993.
41. Gholve PA, Scher DM, Khakharia S, Widmann RF, Green DW. Osgood Schlatter syndrome. Curr Opin Pediatr 19: 44–50, 2007.
42. Griffiths LJ, Cortina-Borja M, Sera F, Pouliou T, Geraci M, Rich C, Cole TJ, Law C, Joshi H, Ness AR, Jebb SA, Dezateux C. How active are our children? Findings from the Millennium Cohort study. BMJ Open 2013;3:e002893. doi:10.1136/bmjopen-2013- 002893.
43. Guagliano J, Rosenkranz R, Kolt G. Girls' physical activity levels during organized sports in Australia. Med Sci Sports Exerc 45: 116–122, 2013.
44. Haff GG. Periodization strategies for youth development. In: Strength and Conditioning for Young Athletes: Science and Application. Lloyd R.S., Oliver J.L., eds. Oxford, United Kingdom: Routledge Publishing. pp. 149–168, 2013.
45. Hall R, Barber Foss KB, Hewett TE, Myer GD. Sports specialization is associated with an increased risk of developing patellofemoral pain in adolescent female athletes. J Sport Rehabil 24: 31–35, 2015.
46. Heyworth BE, Green DW. Lower extremity stress fractures in pediatric and adolescent athletes. Curr Opin Pediatr 20: 58–61, 2008.
47. Hootman JM, Dick R, Agel J. Epidemiology of collegiate injuries for 15 sports: Summary and recommendations for injury prevention initiatives. J Athl Train 42: 311–319, 2007.
48. Iga J, George K, Lees A, Reilly T. Cross-sectional investigation of indices of isokinetic leg strength in youth soccer players and untrained individuals. Scand J Med Sci Sports 19: 714–719, 2009.
49. Jayanthi N, Dechert A, Durazo R, Dugas L, Luke A. Training and sports specialization risks in junior elite tennis players. J Med Sci Tennis 16: 14–20, 2011.
50. Kenttä G, Hassmén P, Raglin JS. Training practices and overtraining syndrome in Swedish age-group athletes. Int J Sports Med 22: 460–465, 2001.
51. Kirk D. Physical education, youth sport and lifelong participation: The importance of early learning experiences. Eur Phys Educ Rev 11: 239–255, 2005.
52. Kocher MS, Waters PM, Micheli LJ. Upper extremity injuries in the paediatric athlete. Sports Med 30: 117–135, 2000.
53. Kruse D, Lemmen B. Spine injuries in the sport of gymnastics. Curr Sports Med Rep 8: 20–28, 2009.
54. Lai SK, Costigan SA, Morgan PJ, Lubans DR, Stodden DF, Salmon J, Barnett LM. Do school-based interventions focusing on physical activity, fitness, or fundamental movement skill competency produce a sustained impact in these outcomes in children and adolescents? A systematic review of follow-up studies. Sports Med 44: 67–79, 2014.
55. Leek D, Carlson JA, Cain KL, Henrichon S, Rosenberg D, Patrick K, Sallis JF. Physical activity during youth sports practices. Arch Pediatr Adolesc Med 165: 294–299, 2011.
56. Lidor R, Lavyan Z. A retrospective picture of early sport experiences among elite and near-elite Israeli athletes: Developmental and psychological perspectives. Int J Sport Psychol 33: 269–289, 2002.
57. Lloyd RS, Faigenbaum AD, Stone MH, Oliver JL, Jeffreys I, Moody JA, Brewer C, Pierce K, McCambridge TM, Howard R, Herrington L, Hainline B, Micheli LJ, Jaques R, Kraemer WJ, McBride MG, Best TM, Chu DA, Alvar BA, Myer GD. Position statement on youth resistance training: The 2014 international consensus. Br J Sports Med 48: 498–505, 2014.
58. Lloyd RS, Oliver JL. The youth physical development model: A new approach to long-term athletic development. Strength Cond J 34: 61–72, 2012.
59. Lloyd RS, Oliver JL, Faigenbaum AD, Myer GD, De Ste Croix M. Chronological age versus biological maturation: Implications for exercise programming in youth. J Strength Cond Res 28: 1454–1464, 2014.
60. Lloyd RS, Oliver JL, Radnor J, Rhodes B, Faigenbaum AD, Myer GD. Relationships between functional movement screen scores, maturation, and physical performance in young soccer players. J Sports Sci 33: 11–19, 2015.
61. Lonsdale C, Hodge K, Rose E. Athlete burnout in elite sport: A self-determination perspective. J Sports Sci 27: 785–795, 2009.
62. Lonsdale C, Rosenkranz RR, Peralta LR, Bennie A, Fahey P, Lubans DR. A systematic review and meta-analysis of interventions designed to increase moderate-to-vigorous physical activity in school based physical education lessons. Prev Med 56: 152–161, 2013.
63. Lopes VP, Rodrigues LP, Maia JA, Malina RM. Motor coordination as a predictor of physical activity in childhood. Scand J Med Sci Sports 21: 663–669, 2011.
64. Lubans DR, Morgan PJ, Cliff DP, Barnett LM, Okely AD. Fundamental movement skills in children and adolescents. Sports Med 40: 1019–1035, 2010.
65. Luhmann SJ, Schoenecker PL, Dobbs MB, Gordon JE. Adolescent patellofemoral pain: Implicating the medial patellofemoral ligament as the main pain generator. J Child Orthop 2: 269–277, 2008.
66. Luke A, Lazaro RM, Bergeron MF, Keyser L, Benjamin H, Brenner J, d'Hemecourt P, Grady M, Philpott J, Smith A. Sports-related injuries in youth athletes: Is overscheduling a risk factor? Clin J Sport Med 21: 307–314, 2011.
67. Malina RM, Bouchard C, Bar-Or O. Growth, Maturation and Physical Activity. Champaign, IL: Human Kinetics, 2004.
68. Matos NF, Winsley RJ, Williams CA. Prevalence of nonfunctional overreaching/overtraining in youth. Med Sci Sports Exerc 43: 1287–1294, 2011.
69. Matricciani L, Olds T, Petkov J. In search of lost sleep: Secular trends in the sleep time of school-aged children and adolescents. Sleep Med Rev 16: 203–211, 2012.
70. McGladrey BW, Hannon JC, Faigenbaum AD, Shultz BB, Shaw JM. High school physical educators' and sport coaches' knowledge of resistance training principles and methods. J Strength Cond Res 28: 1433–1442, 2014.
71. McGuigan MR, Tatasciore M, Newton RU, Pettigre S. Eight weeks of resistance training can significantly alter body composition in children who are overweight or obese. J Strength Cond Res 23: 80–85, 2009.
72. McHugh MP. Oversized young athletes: A weighty concern. Br J Sports Med 44: 45–49, 2010.
73. Meussen R, Duclos M, Foster C, Fry A, Gleeson M, Nieman D, Raglin J, Rietjens G, Steinacker J, Urhausen A. Prevention, diagnosis, and treatment of the overtraining syndrome: Joint consensus statement of the European College of Sport Science and the American College of Sports Medicine. Med Sci Sports Exerc 45: 186–205, 2013.
74. Meeusen R, Duclos M, Gleeson M, Rietjens G, Steinacker J, Urhausen A. Prevention, treatment and diagnosis of the overtraining syndrome. Eur J Sport Sci 6: 1–14, 2006.
75. Micheli L, Natsis KI. Preventing injuries in team sports: What the team physician needs to know. In: FIMS Team Physician Manual (3rd ed.). Micheli L.J., Pigozzi F., Chan K.M., Frotnera W.R., Bachl N., Smith A.D., Alenabi S.T., eds. London, United Kingdom: Routledge, 2013. pp. 505–520.
76. Moesch K, Elbe AM, Hauge MLT, Wilkman JM. Late specialization: The key to success in centimeters, grams, or seconds (cgs) sport. Scand J Med Sci Sports 21: e282–e290, 2011.
77. Moliner-Urdiales D, Ruiz JR, Ortega FB, Jiménez-Pavón D, Vicente-Rodriguez G, Rey-López JP, Martinez-Gómez D, Casajus JA, Mesana MI, Marcos A, Noriega-Borge MJ, Sjöström M, Castillo MJ, Moreno LA; AVENA HELENA Study Groups. Secular trends in health-related physical fitness in Spanish adolescents: The AVENA and HELENA studies. J Sci Med Sport 13: 584–588, 2010.
78. Moody JM, Naclerio F, Green P, Lloyd RS. Motor skill development in youths. In: Strength and Conditioning for Young Athletes: Science and Application. Lloyd R.S., Oliver J.L., eds. Oxford, United Kingdom: Routledge Publishing, 2013. pp. 49–65.
79. Mostafavifar AM, Best TM, Myer GD. Early sport specialisation, does it lead to long-term problems? Br J Sports Med 47: 1060–1061, 2013.
80. Mountjoy M, Andersen L, Armstrong N, Biddle S, Boreham C, Bedenbeck H, Ekelund U, Engebretsen L, Hardman K, Hills A, Kahlmeier S, Kriemler S, Lambert E, Ljungqvist A, Matsudo V, McKay H, Micheli L, Pate R, Riddoch C, Schamasch P, Sundberg C, Tomkinson G, van Sluijs E, van Mechelen W. International Olympic Committee consensus statement on the health and fitness of young people through physical activity and sport. Br J Sports Med 45: 839–848, 2011.
81. Mountjoy M, Armstrong N, Bizzini L, Blimkie C, Evans J, Gerrard D, Hangen J, Knoll K, Micheli L, Sangenis P, Van Mechelen W. IOC consensus statement: “Training the elite child athlete”. Br J Sports Med 42: 163–164, 2008.
82. Myer GD, Faigenbaum AD, Chu DA, Falkel J, Ford KR, Best TM, Hewett TE. Integrative training for children and adolescents: Techniques and practice for reducing sports-related injuries and enhancing athletic performance. Phys Sportsmed 39: 74–84, 2011.
83. Myer GD, Faigenbaum AD, Ford KR, Best TM, Bergeron M, Hewett TE. When to initiate integrative neuromuscular training to reduce sports-related injuries and enhance health in youth? Curr Sports Med Rep 10: 157–166, 2011.
84. Myer GD, Faigenbaum AD, Foss KB, Xu Y, Khoury J, Dolan LM, McCambridge TM, Hewett TE. Injury initiates unfavourable weight gain and obesity markers in youth. Br J Sports Med 48: 1477–1481, 2014.
85. Myer GD, Faigenbaum AD, Stracciolini A, Hewett TE, Micheli LJ, Best TM. Exercise deficit disorder in youth: A paradigm shift toward disease prevention and comprehensive care. Curr Sports Med Rep 12: 248–255, 2013.
86. Myer GD, Ford KR, Barber Foss KD, Goodman A, Ceasar A, Rauh MJ, Divine JG, Hewett TE. The incidence and potential pathomechanics of patellofemoral pain in female athletes. Clin Biomech (Bristol, Avon) 25: 700–707, 2010.
87. Myer GD, Ford KR, Brent JL, Hewett TE. The effects of plyometric versus dynamic balance training on power, balance and landing force in female athletes. J Strength Cond Res 20: 345–353, 2006.
88. Myer GD, Ford KR, McLean SG, Hewett TE. The effects of plyometric versus dynamic stabilization and balance training on lower extremity biomechanics. Am J Sports Med 34: 445–455, 2006.
89. Myer GD, Ford KR, Palumbo JP, Hewett TE. Neuromuscular training improves performance and lower-extremity biomechanics in female athletes. J Strength Cond Res 19: 51–60, 2005.
90. Myer GD, Lloyd RS, Brent JL, Faigenbaum AD. How young is too young to start training? ACSMs Health Fit J 17: 14–23, 2013.
91. Myer GD, Sugimoto D, Thomas S, Hewett TE. The influence of age on the effectiveness of neuromuscular training to reduce anterior cruciate ligament injury in female athletes: A meta-analysis. Am J Sports Med 41: 203–215, 2013.
92. National Association for Sport and Physical Education. Shape of the Nation Report: Status of Physical Education in the USA. Reston, VA: American Alliance for Health, Physical Education, Recreation and Dance, 2010.
93. National Association for Sport and Physical Education. Shape of the Nation Report: Status of Physical Education in the USA. Reston, VA: American Alliance for Health, Physical Education, Recreation and Dance, 2012.
94. Office for Standards in Education, Children's Services and Skills (Ofsted). Beyond 2012—Outstanding Physical Education for All. No: 120367. Manchester, UK: Ofsted, 2013.
95. Ogden JA, Ganey TM, Hill JD, Jaakkola JI. Sever's injury: A stress fracture of the immature calcaneal metaphysis. J Pediatr Orthop 24: 488–492, 2004.
96. Oliver JL, Brady A, Lloyd RS. Well-being of youth athletes. In: Strength and Conditioning for Young Athletes: Science and Application. Lloyd R.S., Oliver J.L., eds. Oxford, United Kingdom: Routledge Publishing, 2013. pp. 213–225.
97. Oliver JL, Lloyd RS, Meyers RW. Training elite child athletes: Welfare and well-being. Strength Cond J 33: 73–79, 2011.
98. Ommundsen Y, Roberts GC, Lemyre PN, Miller BW. Parental and coach support or pressure on psychological outcomes of pediatric athletes in soccer. Clin J Sport Med 16: 522–526, 2006.
99. Ortgea FB, Konstable K, Pasquali E, Ruiz JR, Hurtig-Wennlöf A, Mäestu J, Löf M, Harro J, Bellocco R, Labayen I, Veidebaum T, Sjöström M. Objectively measured physical activity and sedentary time during childhood, adolescence and young adulthood: A cohort study. PLoS One 8: e60871, 2013.
100. Pascual-Garrido C, Moran CJ, Green DW, Cole BJ. Osteochondritis dissecans of the knee in children and adolescents. Curr Opin Pediatr 25: 46–51, 2013.
101. Philippaerts RM, Vaeyens R, Janssens M, Van Renterghem B, Matthys D, Craen R, Bourgois J, Vrijens J, Beunen GP, Malina RM. The relationship between peak height velocity and physical performance in youth soccer players. J Sports Sci 24: 221–230, 2006.
102. Rabinowickz T. The differentiated maturation of the cerebral cortex. In: Human Growth: A Comprehensive Treatise, Postnatal Growth: Neurobiology. Falkner F., Tanner J., eds. 2. New York, NY: Plenum, 1986.
103. Raglin J, Sawamura S, Alexiou S, Hassmén P, Kenttä G. Training practices and staleness in 13-18-year-old swimmers: A cross-cultural study. Pediatr Exerc Sci 12: 61–70, 2000.
104. Ratel S, Duche P, Williams CA. Muscle fatigue during high-intensity exercise in children. Sports Med 36: 1031–1065, 2006.
105. Richmond SA, Kang J, Emery CA. Is body mass index a risk factor for sport injury in adolescents? J Sci Med Sport 16: 401–405, 2013.
106. Roth MA, Millett CJ, Mindell JS. The contribution of active travel (walking and cycling) in children to overall physical activity levels: A national cross sectional study. Prev Med 54: 134–139, 2012.
107. Runhaar J, Collard DCM, Kemper HCG, van Mechelen W, Chinapaw M. Motor fitness in Dutch youth: Differences over a 26-year period (1980-2006). J Sci Med Sport 13: 323–328, 2010.
108. Sandercock GRH, Voss C, Dye L. Associations between habitual school-day breakfast consumption, body mass index, physical activity and cardiorespiratory fitness in English schoolchildren. Eur J Clin Nutr 64: 1086–1092, 2010.
109. Schranz N, Tomkinson G, Olds T. What is the effect of resistance training on the strength, body composition and psychosocial status of overweight and obese children and adolescents? A systematic review and a meta-analysis. Sports Med 43: 893–907, 2013.
110. Schreiber J, Goodgold S, Moerchen V, Remec N, Aaron C, Kreger A. A description of professional pediatric physical therapy education. Pediatr Phys Ther 23: 201–204, 2011.
111. Shaibi G, Cruz M, Ball G, Weigensberg MJ, Crespo NC, Goran MI. Effects of resistance training on insulin sensitivity in overweight Latino adolescent males. Med Sci Sports Exerc 38: 1208–1215, 2006.
112. Sothern MS, Loftin JM, Udall JN, Suskind RM, Ewing TL, Tang SC, Blecker U. Inclusion of resistance exercise in a multidisciplinary outpatient treatment program for preadolescent obese children. South Med J 92: 585–592, 1999.
113. Stein CJ, Micheli LJ. Overuse injuries in youth sports. Phys Sportsmed 38: 102–108, 2010.
114. Steptoe A, Butler N. Sports participation and emotional wellbeing in adolescents. Lancet 29: 1789–1792, 1996.
115. Stodden DF, Gao Z, Goodway JD, Langendorfer SJ. Dynamic relationships between motor skill competence and health-related fitness in youth. Pediatr Exerc Sci 26: 231–241, 2014.
116. Stodden DF, Goodway JD, Langendorfer SJ, Roberton MA, Rudisill ME, Garcia C, Garcia LE. A developmental perspective on the role of motor skill competence in physical activity: An emergent relationship. Quest 60: 290–306, 2008.
117. Stovitz SD, Johnson RJ. “Underuse” as a cause for musculoskeletal injuries: Is it time that we started reframing our message? Br J Sports Med 40: 738–739, 2006.
118. Stratton G, McWhannell N, Foweather L, Henaghan J, Graves L, Ridgers ND, Hepples J. The A-CLASS Project Research Findings: Summary Report. Liverpool, United States: Sportslinx, 2009.
119. Taheri S. The link between short sleep duration and obesity: We should recommend more sleep to prevent obesity. Arch Dis Child 91: 881–884, 2006.
120. Tammelin T, Näyhä S, Laitinen J, Rintamäki H, Järveline MR. Physical activity and social status in adolescence as predictors of physical inactivity in adulthood. Prev Med 37: 375–381, 2003.
121. Teeple JB, Lohman TG, Misner JE, Boileau RA, Massey BH. Contribution of physical development and muscular strength to the motor performance capacity of 7 to 12 year old boys. Br J Sports Med 9: 122–129, 1975.
122. Telama R, Yang X, Viikari J, Välimäki I, Wanne O, Raitakari O. Physical activity from childhood to adulthood: A 21 year tracking study. Am J Prev Med 28: 267–273, 2005.
123. Terry PC, Lane AM, Lane HJ, Keohane L. Development and validation of a mood measure for adolescents. J Sports Sci 17: 861–872, 1999.
124. Tomkinson GR, Léger L, Olds T, Cazorla G. Secular trends in the fitness of children and adolescents (1980-2000). Sports Med 33: 385–400, 2003.
125. Tudor-Locke C, Johnson WD, Katzmarzyk PT. Accelerometer-determined steps per day in US children and youth. Med Sci Sports Exerc 42: 2244–2250, 2012.
126. Tveter AT, Holm I. Influence of thigh muscle strength and balance on hop length in one-legged hopping in children aged 7–12 years. Gait Posture 32: 259–262, 2010.
127. Valovich-McLeod TC, Decoster LC, Loud KJ, Micheli LJ, Parker T, Sandrey MA, White C. National Athletic Trainers' Association position statement: Prevention of pediatric overuse injuries. J Athl Train 46: 206–220, 2011.
128. Wade SM, Pope ZC, Simonson SR. How prepared are college freshmen athletes for the rigors of college strength and conditioning? A survey of college strength and conditioning coaches. J Strength Cond Res 28: 2746–2753, 2014.
129. Weiler R, Allardyce S, Whyte GP, Stamatakis E. Is the lack of physical activity strategy for children complicit mass child neglect? Br J Sports Med 48: 1010–1013, 2014.
130. Whitehead ME. The concept of physical literacy. Eur J Phys Educ 6: 127–138, 2001.
131. World Health Organization. Global Recommendations on Physical Activity for Health. Geneva, Switzerland: WHO Press, 2010.
132. YMCA of the USA. YMCAs expand programs to respond to nation's growing health crisis. Available at: http://www.ymca.net
. Accessed March 21, 2008.