A growing number of young athletes are involved in resistance training in schools, fitness centers, and sports-training facilities (13,61). Over the past decade, evidence-based reports have emerged regarding both the safety and efficacy of resistance training in children and adolescents and the acceptance of pediatric resistance training by medical, fitness, and sport organizations has become widespread (2,3,13). Nowadays, physical education curricula include activities that improve muscular strength, and training programs specifically designed to enhance sports performance (especially among young athletes) have become a top 10 fitness trend for 2010 (58,72). Thus, as more children and adolescents get involved in resistance training in schools, health clubs, and sport training centers, it is important to establish safe and effective guidelines by which resistance exercise can improve the health, fitness, and sports performance of younger populations.
In this article, the term resistance training refers to a method of conditioning that involves the progressive use of a wide range of resistive loads, different movement velocities, and a variety of training modalities including weight machines, free weights (dumbbells and barbells), elastic bands, medicine balls, and body weight. The term resistance training is distinguished from the sports of weightlifting and powerlifting in which athletes periodically train with heavy loads and attempt to lift maximal amounts of weight in competition. For ease of discussion, the terms pediatric, youth, and young refer to children and adolescents.
POTENTIAL BENEFITS OF PEDIATRIC RESISTANCE TRAINING
While a majority of the pediatric research has focused on activities that enhance cardiorespiratory fitness, recent findings indicate that resistance training can offer unique benefits for children and adolescents when appropriately prescribed and supervised (13,48). In addition to enhanced muscular strength and motor skill performance, regular participation in a pediatric resistance training can facilitate weight control, strengthen bone, and increase a young athlete's resistance to sports-related injuries (11,55). Further, since good health habits established during childhood may carry over into adulthood (71), the positive influence of these habits on the adult lifestyle should be recognized by teachers, coaches, and health care providers. The potential benefits of pediatric resistance training are outlined in Table 1.
The influence of resistance training on body composition has become an important topic of investigation, given that the prevalence of obesity among children and adolescents continues to increase (14). Although obese youth traditionally have been encouraged to participate in aerobic activities, excess body weight hinders the performance of weight-bearing physical activities such as jogging and increases the risk of musculoskeletal overuse injuries. Further, obese youth often lack the motor skills and confidence to be physically active, and they actually may perceive prolonged periods of aerobic exercise to be boring or discomforting. As noted by Stodden and colleagues, there is a negative spiral of disengagement, whereby youth with low levels of motor skill competence engage in less physical activity, which in turn leads to increased weight gain (69). In support of these observations, others observed that total body fat was inversely related to minutes of physical activity per day in children (10).
Although the treatment of pediatric obesity is complex, exposure to resistance exercise (along with behavioral counseling and nutrition education) may provide a gateway for overweight and obese youth to initiate exercise activities. From regular participation in resistance exercise, they may gain confidence in their ability to be physically active, which in turn may lead to a noticeable improvement in muscle strength, favorable changes in body composition, and an increase in regular physical activity (including recreational sports). Our observations suggest that overweight and obese youth enjoy resistance training because it is not aerobically taxing and it provides an opportunity for participants to enhance fitness performance while gaining confidence in their abilities to be physically active.
Several studies have reported favorable changes in body composition in children and adolescents who were obese or at risk for obesity following participation in a progressive resistance training program (44,65,67). Shaibi and colleagues observed a significant decrease in body fat and a significant increase in insulin sensitivity after 16 wk of resistance training in overweight adolescent males (65). Because overweight children and adolescents with low muscle fitness are reported to have the poorest metabolic risk profile (68), the protective effects of muscular fitness on metabolic health in youth should not be overlooked by health care providers who continue to embrace the challenge of dealing with overweight and obese youth.
The traditional fears and misinformed concerns that resistance training is harmful to the immature skeleton of young lifters have been replaced by scientific evidence that indicates that childhood and adolescence may be the opportune time for the bone-modeling and remodeling process to respond to the tensile and compressive forces associated with weight-bearing activities (3,73). If age-specific resistance training guidelines are followed with consumption of proper nutrients (e.g., adequate calcium and vitamin D) (4), regular participation in specialized fitness programs that include resistance exercise can play a critical role in bone mass acquisition during the pediatric years (73). Because low levels of peak bone mass are a significant risk factor of osteoporosis and associated fractures, regular participation in programs that maximize peak bone mass during childhood and adolescence may be an effective strategy for reducing the risk of osteoporosis later in life (25). While weight-bearing activities (particularly resistance exercise) can be an osteogenic stimulus during adulthood (22), resistance training may be most beneficial during childhood and adolescence because the mechanical stress from this type of training may act synergistically with growth-related increases in bone mass (3,73).
In support of these results, previous reports of adolescent weightlifters who regularly performed multijoint lifts with relatively heavy loads have been found to have levels of bone mineral density and bone mineral content significantly greater than age-matched control subjects (8,74). While additional clinical trials are needed to define more precisely the exercise prescription for optimizing bone development in youth, the importance of participating in sports and weight-bearing physical activities as a lifetime activity should not be overlooked, as training-induced gains in bone health may be lost over time if the program is not continued (23).
Although the total elimination of sports-related injuries is an unrealistic goal, appropriately designed and sensibly progressed conditioning programs that include resistance training may help reduce the likelihood of sports-related injuries in young athletes. Owing to the apparent decline in free time physical activity among children and adolescents (57,59), it seems that the musculoskeletal system of some aspiring young athletes may not be prepared for the demands of sports practice and competition. In one study, it was reported that children engaged in approximately 3 h·d−1 of moderate to vigorous physical activity (MVPA), but adolescents were only engaging in MVPA for 49 min·d−1 on weekdays and 35 min·d−1 on the weekend (57). Consequently, the supporting structures of some young athletes may be ill-prepared to handle the demands of weekly sports practice sessions and weekend competitions.
By addressing the risk factors associated with youth sport injuries (e.g., low fitness level, muscle imbalances, and errors in training), Micheli suggested that both acute and overuse injuries could be reduced by 15%-50% (46). Heidt and colleagues were able to significantly reduce injury rates with the addition of a preseason conditioning regimen in adolescent female soccer players (26). Cahill and Griffith incorporated resistance training into their preseason program for adolescent football teams and reported a reduction in nonsurgical and surgical knee injuries over four competitive seasons (5). Hejna et al. reported that young athletes (13-19 yr) who incorporated resistance training in their exercise regimen suffered fewer injuries and recovered from injuries with less time spent in rehabilitation compared with teammates who did not resistance train (28). Protocols incorporating resistance training into preseason and inseason conditioning programs are predictive of future injury risk as well as anterior cruciate ligament injuries in adolescent female athletes (29,32). While there is not one combination of exercises, sets, and repetitions that has proven to optimize training adaptations, these data indicate that multifaceted programs that increase muscle strength, enhance movement mechanics, and improve functional abilities appear to be the most effective strategy for reducing sports-related injuries in young athletes.
Clearly, participation in physical activity should not begin with competitive sport but should evolve out of preparatory fitness conditioning that is sensibly progressed over time. Although there are many mechanisms to potentially reduce sports-related injuries (e.g., coaching education, safe equipment, proper nutrition), enhancing physical fitness as a preventative health measure is considered a cornerstone of multicomponent programs for school-aged youth. This is an important consideration for health care providers who often perform preparticipation physical examinations to assess a young athlete's readiness for sport (35). In addition to the medical examination (including a musculoskeletal assessment), health care providers should inquire about a patient's participation in physical activities over the past few months. Because training errors (e.g., too much, too soon.) are a common theme in many sports-related injuries in youth (46), there is an ongoing need to ensure that aspiring young athletes participate in multicomponent conditioning programs before the start of the sport season and continue training in a modified program throughout the competitive season.
SPECIAL CONSIDERATIONS FOR TRAINING FOR GIRLS
While musculoskeletal growth and development show very similar trends between genders, male and female strength and coordination (neuromuscular) patterns diverge significantly during and after puberty (31). Boys naturally demonstrate that power, strength, and body coordination increase with chronological age, which correlates to maturational stage, whereas untrained girls on average show little improvement in strength, balance, and power throughout puberty (31,35,43,62). For example, vertical jump height (a measure of whole-body power) increases steadily in boys during puberty but not in girls (62). This puberty-related divergence in neuromuscular development between boys and girls may explain, at least in part, gender-related differences in injury risk observed in post-pubertal female athletes (1,33,35).
Multifaceted training programs that combine resistance training, plyometric training (with education on jumping and landing techniques), postural balance, and body position control (proprioception) have been found to enhance movement biomechanics and lower extremity strength in adolescent girls (49-55). Observed relative gains in girls may be greater than in boys because baseline neuromuscular performance levels are lower on average in girls versus boys (20,35,40,54,62). Girls have been shown to improve strength measures up to 92% with just 6 wk of training (54). In addition to reduced knee injuries in adolescent (30) and mature female athletes (56), regular participation in a multifaceted resistance training program also may induce measures of the neuromuscular spurt, which typically are not seen in females (54). Of potential interest to sports medicine professionals, resistance training timed with growth and development may induce the desired neuromuscular spurt, which may improve sports performance and improve biomechanics related to injury risk in young girls (34,54). Cumulatively, these findings indicate that young female athletes should participate regularly in multifaceted resistance training programs.
RISKS AND CONCERNS
Current findings from pediatric resistance training studies indicate a low risk of injury in children and adolescents who follow age-appropriate training guidelines (18,24,42). A traditional concern associated with youth resistance training is the potential for injury to the physis or growth plate in a young lifter's body. The growth plate can be three to five times weaker than surrounding connective tissue, and it may be less resistant to shear and tension forces (66). Injury to this section of bone could result in time lost from training, significant discomfort, and growth disturbances (6). Although a few retrospective case reports noted injury to the growth cartilage in youth (18), most of these injuries were caused by improper lifting techniques, poorly chosen training loads, or lack of qualified adult supervision. For example, in one case report, a 13-yr-old boy suffered bilateral fracture separations of the distal radial epiphyses when he lost control of a barbell as he attempted to press a 30-kg weight overhead while exercising alone in a makeshift gymnasium at home (38). It is unclear from this report whether this teenager received instruction on proper resistance training procedures or if he was involved in an activity without qualified supervision. Future reports should provide details of predisposing factors to better understand the true risk of injury to the physis in young lifters.
Injury to the growth cartilage has not been reported in any prospective youth resistance training research study, and there is no evidence to suggest that resistance training will negatively impact growth and maturation during childhood and adolescence (18,42). To date, only three published training studies have reported resistance training-related injuries in young lifters, namely, anterior shoulder pain that resolved within 1 wk of rest (63), a strain of a shoulder muscle that resulted in one missed training session (41), and nonspecific anterior thigh pain that resolved with 5 min of rest (64). A review of these findings revealed estimated injury rates of 0.176, 0.053, and 0.055 per 100 participant hours, respectively, which suggests that supervised resistance training protocols are relatively safe for youth (18). Significant gains in strength without any report of injury also have been reported in prospective studies in which weightlifting movements (including modified cleans, pulls, and presses) were incorporated into youth resistance training programs (7,16,21).
While the available data indicate that the injury occurrence in pediatric resistance training studies is either very low or nil (18,24,42), professionals who prescribe resistance exercise should be mindful of the inherent risk associated with this type of training, cognizant of safety precautions, and aware of the potential risk for repetitive use soft-tissue injuries. For example, Quatman and colleagues reported that the trunk was the most frequently injured body part for both men and women between the ages of 14 and 30 yr who presented to U.S. emergency departments from weightlifting injuries (61). Since lower back pain has become a significant health concern among adolescents (37), there appears to be a role for preventative interventions that enhance the strength, local muscular endurance, and stability of the lower back to reduce the prevalence or severity of lower back injuries in young lifters. From our experience, some young lifters spend too much time training their mirror muscles (e.g., chest: bench press; arms: biceps curl) and not enough time (or no time at all) strengthening their trunk or posterior chain musculature. Thus, observed injuries to the lower back in young lifters may be due, at least in part, to poor program design. Other factors such as improper exercise technique and inappropriate progression of training loads also may increase the risk of soft-tissue injury.
If pediatric resistance training guidelines are not followed, there is the potential for serious injury. For example, it has been reported that unsafe behavior, equipment malfunction, and lack of qualified supervision increase the risk of injury in young children who exercise at home (39). Myer and colleagues recently reported that two-thirds of resistance training-related injuries sustained by 8- to 13-yr-old patients who reported to emergency departments in the United States were to the hand and foot, and most were related to dropping and pinching (47) (Fig. 1). These findings underscore the importance of qualified supervision, safe exercise equipment, and strict adherence to pediatric resistance training guidelines at home, school, and sports-training centers.
PEDIATRIC RESISTANCE TRAINING GUIDELINES
A prerequisite for the development and administration of safe, effective, and enjoyable youth resistance training programs is an understanding of established training principles and an appreciation for the physical and psychosocial uniqueness of children and adolescents. Qualified and enthusiastic instruction not only enhances participant safety and enjoyment, but direct supervision of youth resistance training programs can improve program adherence and optimize strength gains (9). Although there is no minimum age requirement at which children can begin resistance training, all participants must be mentally and physically ready to comply with coaching instructions and undergo the stress of a training program. In general, if a child is ready for participation in sport activities (generally age 7 or 8), then he or she is ready for some type of resistance training.
There does not appear to be one optimal combination of sets, repetitions, and exercises that will promote favorable adaptations in young athletes. Rather, the sensible integration of different training methods and the periodic manipulation of program variables over time will keep the training stimulus effective, challenging, and pleasurable for the participants. We refer to this concept as fitness integration because it incorporates a combination of performance-enhancing and injury-reducing components (e.g., strength, power, and balance) into one fitness program. This type of training does not necessitate expensive equipment, but it does require qualified instruction, a systematic progression of training variables, and an understanding of pediatric resistance exercise guidelines (3,13). In short, the act of resistance training in and of itself does not ensure that favorable changes in fitness and performance will be realized. Rather, individual effort combined with a well-designed training program ultimately will determine the adaptations that take place.
When designing resistance training programs for young athletes, it is important to consider the total exercise dose, which includes sports practice and competition as well as free play, physical education, and possibly private training sessions. Some young athletes with relatively immature musculoskeletal systems may not be able to tolerate the same exercise dose as their teammates. Because of the interindividual variability of stress tolerance, each young athlete should be treated as an individual, and coaches must be aware of incipient signs of overtraining, which would require a modification of the training program. A reduction in sports performance and an increased risk of injury can result if resistance exercises are simply added onto a young athlete's training schedule.
The acute program design variables that should be considered when designing pediatric resistance training programs include 1) warm-up and cool-down, 2) selection and order of exercise, 3) training intensity and volume, 4) rest intervals between sets and exercises, and 5) repetition velocity. Table 2 summarizes pediatric resistance training guidelines. Detailed descriptions of pediatric resistance training programs using different types of equipment are beyond the scope of this article but are available elsewhere (15,45,50).
Warm-Up and Cool-Down
Over the past few years, long-held beliefs regarding the routine practice of warm-up static stretching have been questioned. Lately, there has been rising interest in warm-up procedures that involve the performance of dynamic movements (e.g., hops, skips, jumps, and movement-based exercises for the upper and lower body) designed to elevate core body temperature, enhance motor unit excitability, improve kinesthetic awareness, and maximize active ranges of motion. Warm-up protocols that include moderate- to high-intensity dynamic movements have been found to enhance power performance in young athletes (12,17). A reasonable suggestion is to perform 5-10 min of dynamic activities (e.g., jumping, skipping, and lunging) during the warm-up period and less intense calisthenics and static stretching at the end of the workout.
Selection and Order of Exercise
Weight machines (both child-sized and adult-sized) as well as free weights, elastic bands, medicine balls, and body weight exercises have been used by children and adolescents in clinical- and school-based exercise programs (3,15,55). While each mode of training has advantages and disadvantages, it is important to select exercises that are appropriate for a participant's body size, fitness level, exercise technique experience, and training goals. It is desirable to start with relatively simple exercises and gradually progress to more advanced multijoint movements as confidence and competence improve.
From our experience, resistance training with free weights, medicine balls, and one's own body weight may be particularly beneficial for young athletes who need to enhance motor skill performance, balance, core strength, and muscle power as part of an integrated training program. Increased dynamic balance may help to provide young athletes with a stable core (i.e., pelvis, abdomen, trunk, and hip) that will be better prepared to respond to the high forces generated at the distal body parts during athletic competition (50). During peak height velocity in pubertal athletes, the tibia and femur grow at relatively rapid rates in both sexes (31,70). Rapid growth of the two longest levers (tibia and femur) initiate height increases that concurrently increase height of the center of mass, making muscular control of the trunk more difficult (31,35,50).
Although the isolated effects of core training and balance training on measures of performance have not been demonstrated clearly, the potential benefits of this type of training likely are substantial and combinatory to other modes of conditioning (27). For example, core strengthening and balance training can improve dynamic balance, which may help provide an athlete with a dynamically stable core that can be better prepared to respond to the high forces generated at the distal body parts during athletic competition (36,60). While further study is warranted, the global effects of core strength gains may be best attained with the integration of core strengthening and balance training into a multifaceted resistance training program. Overhead training exercises such as the unilateral loaded walking lunge press are designed to simultaneously improve core strength and dynamic stability during a multiplanar movement progression (Fig. 2).
There are many ways to arrange the sequence of exercises in a resistance training session. Most youth will perform total body workouts several times per week, which involve multiple exercises stressing all major muscle groups each session. In this type of workout, large muscle group exercises should be performed before smaller muscle group exercises, and multiple-joint exercises should be performed before single-joint exercises. Of note, it is desirable to perform more challenging exercises earlier in the workout when the neuromuscular system is less fatigued. Thus, if a child is learning how to perform a weightlifting movement or a plyometric exercise, this type of exercise should be performed early in the training session so that the child can practice the exercise without undue fatigue.
Training Intensity and Volume
Training intensity typically refers to the amount of resistance used for a specific exercise, whereas training volume generally refers to the total amount of work performed in a training session. While both of these program variables are significant, training intensity is one of the more important factors in the design of a resistance training program because it is the major stimulus related to changes in muscular fitness. However, to maximize gains in muscular fitness and reduce the risk of injury, youth must first learn how to perform each exercise correctly with a light load (e.g., unloaded barbell) and then gradually progress the training intensity and/or volume without compromising exercise technique.
A simple approach may be to first establish the repetition range, and then by trial and error determine the maximum load that can be handled for the prescribed range. For example, a young lifter may begin resistance training with one or two sets of 10-15 repetitions with a light or moderate load in order to develop proper exercise technique. Depending on individual needs, goals, and abilities, over time the repetition range can be progressed to include additional sets with heavier loads (e.g., 6-10 repetition maximum) on large muscle group exercises to maximize gains in muscle strength. Because of the relative complexity of power exercises (e.g., plyometric or weightlifting movements), note that youth typically perform fewer quality repetitions (≤6) in order to maintain movement speed and efficiency for all repetitions within a set. As training programs become more advanced (and potentially more intense), the importance of reinforcing proper exercise technique and training habits should not be overlooked. Moreover, by periodically varying program variables, long-term performance gains will be optimized, the likelihood of boredom will be reduced, and risk of overuse injuries may decrease.
Rest Intervals Between Sets and Exercises
The length of the rest interval between sets and exercises is an important but often overlooked program variable. While rest intervals of 2-3 min typically are recommended for adult lifters, this guideline may not be consistent with the needs and abilities of younger populations due to growth- and maturation-related differences in response to physical exertion. The available data suggest that children and adolescents can resist fatigue to a greater extent than adults during several repeated sets of resistance exercise (19). Thus, a shorter rest interval (about 1 min) may suffice in children and adolescents when performing a moderate-intensity resistance exercise protocol, although the likelihood that youth with lower levels of strength may recover faster than youth with higher levels of strength should be considered.
The velocity or cadence at which a resistance exercise is performed can affect the adaptations to a training program. While it generally is recommended that youth resistance-train in a controlled manner at a moderate velocity, different training velocities may be used depending on the choice of exercise. For example, plyometric exercises and weightlifting movements are explosive but highly controlled movements that are performed at a high velocity. As part of an integrated resistance training program, we believe that the performance of different training velocities within a training program may provide the most effective training stimulus for young athletes. However, as youth increase movement velocity during training, it is critical that technical performance of each exercise is mastered before progressing to more advanced movements. Instructors should monitor every training session and provide constructive feedback to ensure that athletes maintain proper technical performance of all exercise movements.
Scientific evidence and clinical impressions indicate that resistance training has the potential to offer observable health and fitness value to children and adolescents, provided that appropriate training guidelines are followed and qualified instruction is available. Comprehensive resistance training programs that integrate different elements of physical fitness are most likely to enhance sports performance and reduce the risk of injury. These benefits can be obtained safely by most youth who train under the supervision of a qualified coach and follow age-appropriate resistance training guidelines. Important future research goals should aim to elucidate the mechanisms responsible for the performance enhancement and injury reduction benefits associated with pediatric resistance exercise in order to establish the combination of program variables that may optimize long-term training adaptations and exercise adherence in children and adolescents.
This study was supported in part by the National Institutes of Health Grants R01-AR049735 and R01-AR055563.
1. Alentorn-Geli E, Myer GD, Silvers HJ, et al. Prevention of non-contact anterior cruciate ligament injuries in soccer players. Part 1: Mechanisms of injury and underlying risk factors. Knee Surg. Sports Traumatol. Arthrosc
. 2009; 17:705-29.
2. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription
. 8th ed. Baltimore, MD: Lippincott, Williams and Wilkins; 2010.
3. Behm DG, Faigenbaum AD, Falk B, Klentrou P. Canadian Society for Exercise Physiology position paper: resistance training in children and adolescents. Appl. Physiol. Nutr. Metab
. 2008; 33:547-61.
4. Bueno A, Czepielewski M. The importance for growth of dietary intake of calcium and vitamin D. J. Pediatrics
. 2008; 84:386-94.
5. Cahill B, Griffith E. Effect of preseason conditioning on the incidence and severity of high school football knee injuries. Am. J. Sports Med
. 1978; 6:180-4.
6. Caine D, DiFiori J, Maffulli N. Physeal injuries in children's and youth sports: reasons for concern? Br. J. Sports Med
. 2006; 40:749-60.
7. Channell BT, Barfield JP. Effect of Olympic and traditional resistance training on vertical jump improvement in high school boys. J. Strength Cond. Res
. 2008; 22:1522-7.
8. Conroy BP, Kraemer WJ, Maresh CM, et al. Bone mineral density in elite junior Olympic weightlifters. Med. Sci. Sports Exerc
. 1993; 25:1103-9.
9. Coutts A, Murphy A, Dascombe B. Effect of direct supervision of a strength coach on measures of muscular strength and power in young rugby league players. J. Strength Cond. Res
. 2004; 18:316-23.
10. Dencker M, Thorsson O, Karlsson MK, et al. Daily physical activity related to body fat in children aged 8-11 years. J. Pediatr
. 2006; 149:38-42.
11. Faigenbaum A. Resistance training for children and adolescents: are there health outcomes? Am. J. Lifestyle Med
. 2007; 1:190-200.
12. Faigenbaum A, Kang, J, McFarland J. Acute effects of different warm-up protocols on anaerobic performance in teenage athletes. Pediatr. Exer. Sci
. 2006; 17:64-75.
13. Faigenbaum A, Kraemer W, Blimkie C, et al. Youth resistance training: updated position statement paper from the National Strength and Conditioning Association. J. Strength Cond. Res
. 2009; 23(Suppl. 5):S60-79.
14. Faigenbaum A, Westcott W. Resistance training for obese children and adolescents. President's Council Phys. Fit. Sports
. 2007; 8:1-8.
15. Faigenbaum A, Westcott W. Youth Strength Training
. Champaign, IL: Human Kinetics; 2009.
16. Faigenbaum AD, McFarland JE, Johnson L, et al. Preliminary evaluation of an after-school resistance training program for improving physical fitness in middle school-age boys. Percept. Mot. Skills
. 2007; 104:407-15.
17. Faigenbaum AD, McFarland JE, Schwerdtman JA, et al. Dynamic warm-up protocols, with and without a weighted vest, and fitness performance in high school female athletes. J. Athl. Train
. 2006; 41:357-63.
18. Faigenbaum AD, Myer GD. Resistance training among young athletes: safety, efficacy and injury prevention effects. Br. J. Sports Med
. 2010; 44:56-63.
19. Faigenbaum AD, Ratamess NA, McFarland J, et al. Effect of rest interval length on bench press performance in boys, teens, and men. Pediatr. Exerc. Sci
. 2008; 20:457-69.
20. Ford KR, Myer GD, Smith RL, et al. Use of an overhead goal alters vertical jump performance and biomechanics. J. Strength Cond. Res
. 2005; 19:394-9.
21. Gonzales-Badillo J, Gorostiaga E, Arellano R, Izquierdo M. Moderate resistance training produces more favorable strength gains than high or low volume during a short term training cycle. J. Strength Cond. Res
. 2005; 19:689-97.
22. Guadalupe-Grau A, Fuentes T, Guerra B, Calbet J. Exercise and bone mass in adults. Sports Med
. 2009; 39:439-68.
23. Gustavsson A, Olsson T, Nordstrom P. Rapid loss of bone mineral density of the femoral neck after cessation of ice hockey training: a 6-year longitudinal study in males. J. Bone Min. Res
. 2003; 18:1964-9.
24. Hamill B. Relative safety of weight lifting and weight training. J. Strength Cond. Res
. 1994; 8:53-7.
25. Hansen M, Overgaard K, Riis B, Christiansen C. Role of peak bone mass and bone loss in postmenopausal women. Br. Med. J
. 1991; 303:961-4.
26. Heidt R, Swetterman L, Carlonas R, Traub J, Tekulve F. Avoidance of soccer injuries with preseason conditioning. Am. J. Sports Med
. 2000; 28:659-62.
27. Heitkamp HC, Horstmann T, Mayer F, Weller J, Dickhuth HH. Gain in strength and muscular balance after balance training. Int. J. Sports Med
. 2001; 22:285-90.
28. Hejna WF, Rosenberg A, Buturusis DJ, Krieger A. The prevention of sports injuries in high school students through strength training. National Strength Coaches Assoc. J
. 1982; 4:28-31.
29. Hewett TE, Ford KR, Myer GD. Anterior cruciate ligament injuries in female athletes: part 2, a meta-analysis of neuromuscular interventions aimed at injury prevention. Am. J. Sports Med
. 2006; 34:490-8.
30. Hewett TE, Lindenfeld TN, Riccobene JV, Noyes FR. The effect of neuromuscular training on the incidence of knee injury in female athletes. A prospective study. Am. J. Sports Med
. 1999; 27:699-706.
31. Hewett TE, Myer GD, Ford KR. Decrease in neuromuscular control about the knee with maturation in female athletes. J. Bone Joint Surg. Am
. 2004; 86-A:1601-8.
32. Hewett TE, Myer GD, Ford KR. Reducing knee and anterior cruciate ligament injuries among female athletes: a systematic review of neuromuscular training interventions. J. Knee Surg
. 2005; 18:82-8.
33. Hewett TE, Myer GD, Ford KR. Anterior cruciate ligament injuries in female athletes: part 1, mechanisms and risk factors. Am. J. Sports Med
. 2006; 34:299-311.
34. Hewett TE, Myer GD, Ford KR, et al. Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: a prospective study. Am. J. Sports Med
. 2005; 33:492-501.
35. Hewett TE, Myer GD, Ford KR, JL S. Preparticipation physical exam using a box drop vertical jump test in young athletes: the effects of puberty and sex. Clin. J. Sport Med
. 2006; 16:298-304.
36. Holm I, Fosdahl MA, Friis A, et al. Effect of neuromuscular training on proprioception, balance, muscle strength, and lower limb function in female team handball players. Clin. J. Sport Med
. 2004; 14:88-94.
37. Jeffries L, Milanese S, Grimmer-Somers K. Epidemiology of adolescent spine pain. Spine
. 2007; 23:2630-7.
38. Jenkins N, Mintowt-Czyz W. Bilateral fracture separations of the distal radial epiphyses during weight-lifting. Br. J. Sports Med
. 1986; 20:72-3.
39. Jones C, Christensen C, Young M. Weight training injury trends. Phys. Sports Med
. 2000; 28:61-72.
40. Kraemer WJ, Keuning M, Ratamess NA, et al. Resistance training combined with bench-step aerobics enhances women's health profile. Med. Sci. Sports Exerc
. 2001; 33:259-69.
41. Lillegard WA, Brown EW, Wilson DJ, Henderson R, Lewis E. Efficacy of strength training in prepubescent to early postpubescent males and females: effects of gender and maturity. Pediatr. Rehabil
. 1997; 1:147-57.
42. Malina R. Weight training in youth - growth, maturation and safety: an evidence based review. Clin. J. Sports Med
. 2006; 16:478-87.
43. Malina RM, Bouchard C. Timing and sequence of changes in growth, maturation, and performance during adolescence. Growth, Maturation, and Physical Activity
. Champaign, IL: Human Kinetics; 1991, p. 267-72.
44. McGuigan MR, Tatasciore M, Newton RU, Pettigrew S. Eight weeks of resistance training can significantly alter body composition in children who are overweight or obese. J. Strength. Cond. Res
. 2009; 23:80-5.
45. Mediate P, Faigenbaum A. Medicine Ball for All Kids
. Monterey, CA: Healthy Learning; 2007.
46. Micheli L. Preventing injuries in team sports: what the team physician needs to know. In: Chan K, Micheli L, Smith A, et al. (editors), F.I.M.S. Team Physician Manual
, 2nd ed., Hong Kong: CD Concepts; 2006, p. 555-72.
47. Myer G, Quatman C, Khoury J, Wall E, Hewett T. Youth vs. adult "weightlifting" injuries presented to United States emergency rooms: accidental vs. non-accidental injury mechanisms. J. Strength Cond. Res
. 2009; 23:2054-60.
48. Myer G, Wall E. Resistance training in the young athlete. Oper. Tech. Sports Med
. 2006; 14:218-30.
49. Myer GD, Brent JL, Ford KR, Hewett TE. A pilot study to determine the effect of trunk and hip focused neuromuscular training on hip and knee isokinetic strength. Br. J. Sports Med
. 2008; 42:614-9.
50. Myer GD, Chu DA, Brent JL, Hewett TE. Trunk and hip control neuromuscular training for the prevention of knee joint injury. Clin. Sports Med
. 2008; 27:425-48, ix.
51. 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
. 2006; 20:345-53.
52. Myer GD, Ford KR, Brent JL, Hewett TE. Differential neuromuscular training effects on ACL injury risk factors in "high-risk" versus "low-risk" athletes. BMC Musculoskelet. Disord
. 2007; 8:1-7.
53. 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
. 2006; 34:490-8.
54. Myer GD, Ford KR, Palumbo JP, Hewett TE. Neuromuscular training improves performance and lower-extremity biomechanics in female athletes. J. Strength Cond. Res
. 2005; 19:51-60.
55. Myer GD, Wall EJ. Resistance training in the young athlete. Oper. Tech. Sports Med
. 2006; 14:218-30.
56. Myklebust G, Engebretsen L, Braekken IH, et al. Prevention of anterior cruciate ligament injuries in female team handball players: a prospective intervention study over three seasons. Clin. J. Sport Med
. 2003; 13:71-8.
57. Nader P, Bradley R, Houts R, McRitchie S, O'Brien M. Moderate to vigorous physical activity from ages 9 to 15 years. JAMA
. 2008; 300:295-305.
58. National Association for Sport and Physical Education. Physical Education for Lifetime Fitness
, 2nd ed., Champaign, IL: Human Kinetics; 2005.
59. Nyberg G, Nordenfelt A, Ekelund U, Marcus C. Physical activity patterns measured by accelerometry in 6- to 10-yr-old children. Med. Sci. Sports Exerc
. 2009; 41:1842-8.
60. Paterno MV, Myer GD, Ford KR, Hewett TE. Neuromuscular training improves postural stability in young female athletes. J. Orthop. Sports Phys. Ther
. 2004; 34:305-16.
61. Quatman C, Myer G, Khoury J, Wall E, Hewett T. Sex differences in "weightlifting" injuries presenting to United States emergency rooms. J. Strength Cond. Res
. 2009; 23:2061-7.
62. Quatman CE, Ford KR, Myer GD, Hewett TE. Maturation leads to gender differences in landing force and vertical jump performance: a longitudinal study. Am. J. Sports Med
. 2006; 34:806-13.
63. Rians CB, Weltman A, Cahill BR, et al. Strength training for prepubescent males: is it safe? Am. J. Sports Med
. 1987; 15:483-9.
64. Sadres E, Eliakim A, Constantini N, Lidor R, Falk B. The effect of long term resistance training on anthropometric measures, muscle strength and self-concept in pre-pubertal boys. Ped. Exerc. Sci
. 2001; 13:357-72.
65. Shaibi GQ, Cruz ML, Ball GD, et al. Effects of resistance training on insulin sensitivity in overweight Latino adolescent males. Med. Sci. Sports Exerc
. 2006; 38:1208-15.
66. Smith A, Loud K. Special populations. In: Chan K, Micheli L, Smith A, et al. (editors). F.I.M.S. Team Physicial Manual
, 2nd ed., Hong Kong: CD Concept; 2006, p. 206-34.
67. Sothern M, Loftin J, Udall J, et al. Safety, feasibility and efficacy of a resistance training program in preadolescent youth. Am. J. Med. Sci
. 2000; 319:370-5.
68. Steene-Johannessen J, Anderssen SA, Kolle E, Andersen LB. Low muscle fitness is associated with metabolic risk in youth. Med. Sci. Sports Exerc
. 2009; 41:1361-7.
69. Stodden D, Goodway J, Langendorfer S, et al. A developmental perspective on the role of motor skill competence in physical activity: An emergent relationship. Quest
. 2008; 60:290-306.
70. Tanner JM, Davies PS. Clinical longitudinal standards for height and height velocity for North American children. J. Pediatr
. 1985; 107:317-29.
71. Telama R, Yang X, Viikari J, et al. Physical activity from childhood to adulthood: a 21 year tracking study. Am. J. Prev. Med
. 2005; 28:267-73.
72. Thompson W. Worldwide survey reveals fitness trends for 2010. ACSM Health Fit. J
. 2009; 13:9-16.
73. Vicente-Rodriguez G. How does exercise affect bone development during growth? Sports Med
. 2006; 36:561-9.
74. Virvidakis K, Georgiu E, Korkotsidis A, Ntalles A, Proukakis C. Bone mineral content of junior competitive weightlifters. Int. J. Sports Med
. 1990; 11:244-6.