Version May 2024
INTRODUCTION — The benefits of physical activity and the potential benefits and risks of strength training in children and adolescents are reviewed here. This information can be used by clinicians to counsel children and families regarding the development of an overall physical fitness program that includes strength training. Strength training for adults is discussed separately. (See "Strength training for health in adults: Terminology, principles, benefits, and risks" and "Practical guidelines for implementing a strength training program for adults".)
DEFINITIONS — In the discussion below, the terms "child" and "children" refer to boys and girls who have not yet developed secondary sex characteristics (Tanner stages 1 and 2, ie, preadolescence). Adolescence refers to the period of time between childhood and adulthood (Tanner stages 3 and 4). The term "youth" broadly refers to both children and adolescents. (See "Normal puberty".)
Basic definitions pertaining to exercise and strength training are provided below [1-4]. More detailed discussions of the training principles and physiology of strength training are found separately. (See "Strength training for health in adults: Terminology, principles, benefits, and risks", section on 'Strength training: Definition and key principles' and "Practical guidelines for implementing a strength training program for adults", section on 'Basic physiology of strength training: How we get stronger'.)
●Physical fitness – A set of physical attributes that enable one to perform daily physical activities. Health-related physical fitness encompasses cardiorespiratory endurance, muscular strength and endurance, flexibility, and body composition. Sports-related physical fitness includes the additional components of balance, agility, power, reaction time, speed, and coordination.
●Physical activity – Any bodily movement that results in an increase in energy expenditure.
●Exercise – A subset of physical activity that is carried out for the specific purpose of improving or maintaining one or more of the components of physical fitness. Exercise is planned, structured, and repetitive.
●Strength training (also called resistance training) – The systematic use of various methods of applying resistance to movement to increase one's ability to exert or resist force. Methods of applying resistance may include free weights, bodyweight exercises, weight machines, elastic cords, tubing, or other devices.
●Weight training – The use of free weights (dumbbells (picture 1) and barbells (picture 2)) or weight machines (picture 3) for resistance training.
●Olympic weightlifting – A form of strength training or a competitive sport that contests maximal lifts using two exercises: the snatch (picture 4) and the clean-and-jerk (picture 5).
●Power lifting – A competitive sport that contests maximal lifts using the squat (picture 6), bench press (picture 7), and deadlift (picture 8).
●Bodybuilding – A competitive sport in which strength-training methods are used to increase muscle mass, symmetry, and definition. It does not involve competitive lifts [5].
PHYSICAL ACTIVITY
General guidelines — Reports and recommendations from professional organizations and government agencies have increased public awareness of the health benefits associated with regular physical activity [6-8]. A panel convened by the United States Centers for Disease Control and Prevention (CDC) recommends that school-age children participate in at least 60 minutes per day of moderate to vigorous physical activity (MVPA) (most of which should be aerobic activity) that is age and developmentally appropriate and enjoyable [1,8-12]. As part of the 60 minutes or more of daily physical activity, children and adolescents should include muscle- and bone-strengthening activities on at least three days per week [10,12]. However, a surveillance study published by the CDC in 2017 found that only 26 percent of adolescents met suggested guidelines for aerobic activity, 51 percent for muscle-strengthening exercise, and 20 percent for both [13]. (See 'Duration' below.) Screening children for appropriate types and duration of physical activity is discussed separately. (See "Screening tests in children and adolescents", section on 'Physical activity assessment'.)
Increased levels of physical activity and fitness during childhood and adolescence are associated with reduced risk of disease in adulthood (eg, cardiovascular disease, diabetes, selected cancers, and musculoskeletal conditions) [14]. However, these benefits usually are not the motivating factors for physical activity among children and adolescents. Children and adolescents participate in exercise or strength-training programs to improve physical fitness, performance, body composition, and body image, or to alleviate boredom and to socialize [15]. (See "The benefits and risks of aerobic exercise", section on 'Benefits of exercise'.)
The CDC recommends multifaceted approaches to promote physical activity among young people [1]. Their guidelines suggest that health care providers, schools, the community, and the fitness industry cooperate to provide safe environments and facilities for developmentally appropriate physical activity, as well as appropriate instruction, supervision, and role models for youth. Although physical activity guidelines for adults have been updated several times over the past two decades, recommendations specific to children and adolescents have remained consistent [10,16,17]. The CDC has developed a Youth Physical Activity Guidelines Toolkit that can be used to promote youth physical activity.
Duration — Children should be encouraged to participate in regular physical activity to establish healthy lifestyle habits at an early age. Portions of a child's free time should be devoted to participation in play, recreation, sports, and other physical activities that improve each of the components of physical fitness.
A panel convened by the CDC recommends that school-age children participate in at least 60 minutes per day of MVPA that is developmentally appropriate and enjoyable [8,11]. The activity may occur in the context of play, games, sports, work, transportation, recreation, physical education, or planned exercise [1,8]. Examples of moderate physical activity include hiking, skateboarding, and brisk walking; examples of vigorous physical activity include jumping rope, running, and sports such as soccer, basketball, and ice or field hockey [16]. As part of the 60 minutes per day of MVPA, muscle-strengthening (eg, climbing ropes or jungle gym, bodyweight exercises [push-ups, pull-ups], weightlifting) and bone-strengthening activities (eg, jumping rope, running, skipping) are recommended three days per week [10].
Longitudinal data collected from accelerometers in the Study of Early Child Care and Youth Development (2000 to 2006) indicate that virtually all nine-year-old children met the CDC guideline for MVPA, engaging in an average of approximately three hours of MVPA per day (as measured by an accelerometer) [18,19]. However, by 15 years of age, MVPA declined to an average of 50 minutes per day on weekdays and 37 minutes per day on weekends, with only 32 and 18 percent of 15-year-olds meeting the CDC guidelines for MVPA on weekdays and weekends, respectively. According to the 2010 National Youth Physical Activity and Nutrition Survey, only 15 percent of high school students participate in ≥60 minutes of aerobic physical activity per day [20].
Reduced physical activity during adolescence predicts reduced physical activity in adulthood, which has potential long-term health implications [21]. In a large prospective observational study of physical activity in United States adolescents and young adults (10th grade through post-high school), less than 9 percent of study participants met the recommended minimum of 60 minutes of daily moderate-intensity physical activity [22]. This study found that males tend to be more physically active than females and youth are more physically active on weekdays than on weekends. Subsequent data from the National Health and Nutrition Examination Survey (NHANES; 2007 to 2016) show that 88 percent of boys and 78 percent of girls 12 to 17 years of age self-report some moderate or vigorous physical activity [23]. Among the subjects in this study reporting any activity, females generally reported less than the recommended daily amount.
Overall, the data collected on physical activity suggest that the percentage of youth who meet physical activity recommendations remains relatively low, females participate in less physical activity than males, physical activity levels among youth appear to be related to race and income, and physical activity levels decline as youth move into young adulthood. This decline in physical activity as youth transition into adulthood is associated with an increase in body mass index (BMI) and related medical problems. Exercise in adults is reviewed separately. (See "The benefits and risks of aerobic exercise" and "Exercise for adults: Terminology, patient assessment, and medical clearance" and "Exercise prescription and guidance for adults".)
Benefits of regular physical activity — Several systematic reviews have identified a wide range of benefits derived from regular physical activity in school-age children, although the strength of the evidence supporting these findings is variable [8,14,24,25]:
●Reduced adiposity in overweight youth [26-28]
●Reduction of blood pressure in youth with mild essential hypertension [26,29,30]
●Reduction in cholesterol and/or triglyceride levels in youth with high cholesterol or obesity [31]
●Improved bone health [32-34]
●Improved aerobic fitness [35,36] and cardiometabolic health [37]
●Improved muscular strength and endurance [35]
●Improved psychosocial well-being [38-42]
●Reduced risk of depression [11,37]
●Improved cognitive performance [43-46]
●Improved academic performance [37]
Development and maintenance of muscle strength and endurance is important in the performance of activities of daily living but also may improve performance in recreational or competitive activities [47]. Strength training is a safe and effective method of developing muscular strength and endurance in youth, provided that the program is well designed and supervised and participants are trained in proper techniques [2,3,48,49]. The program should be tailored to the individual with respect to maturation, duration of training, motor skill competency, technical proficiency, and existing strength [2,38,50,51]. (See 'Strength training: Safety and benefits' below and 'Principles of training' below.)
In addition to their immediate benefits, improvements in aerobic fitness achieved during childhood are associated with better health during adulthood [52]. The health benefits of regular physical activity for adults are well established and discussed in detail separately [1]. (See "The benefits and risks of aerobic exercise", section on 'Benefits of exercise'.)
Organized programs — An increasing number of children are participating in organized sports. The younger the participant, the greater are the concerns about safety and benefits.
Young participants are often enticed by the success of professional athletes. The reality is that very few high school senior athletes will be drafted to play professional sports [53]. In addition, college scholarships can motivate young athletes (and parents) to commit to specialized training at an early age. Nonetheless, youth, particularly children, should be encouraged to participate in regular physical activity and exercise for the sake of enjoyment and not merely competition. Emphasis should be given to increasing habitual physical activity.
Chronological age; physical, cognitive, and social maturity; and developmental physiology must be taken into consideration when developing and implementing physical activity and exercise programs for youth. Children have different physiologic responses to exercise than do adults and require different programs to acquire health benefits, develop fitness, and/or improve performance [54-56].
Participation need not begin with competitive sports. Participation may evolve from preparatory physical activity, recreation, or conditioning programs [50]. It is thought that participation in strength-building activities before sports participation may prevent, reduce the risks of, or lessen the severity of sports-related injuries, but there is no conclusive evidence to support this [49,57,58]. (See 'Injury prevention' below.)
Goals — Safe and effective organized activities and sports for children have age- and developmentally appropriate objectives, which include [58]:
●Acquisition of basic motor skills
●Increasing physical activity levels
●Learning social skills (eg, working as a team, good sportsmanship)
●Having fun
Participation in organized activities and sports provides an opportunity for children to learn to follow age- or skill-appropriate rules and to develop self-discipline, self-esteem, and leadership [57].
Organized programs also should teach youth about their bodies, promote injury prevention, and provide education about health-related topics (eg, proper nutrition, hydration, and substance abuse, such as ergogenic aids or anabolic steroids). These programs should contribute to the overall development of the child and the adoption of lifelong exercise behaviors.
Components — General physical conditioning should be part of every organized sports program. Physical fitness should be improved to safely and enjoyably participate in a sport. A well-designed exercise program may increase the likelihood that a child will participate in other activities and develop positive physical activity behaviors [51]. Broadly based participation in a variety of skills and activities is related to increased participation and success in sports later in life [59,60].
A general strength-training program is beneficial as one component of an overall conditioning program, adds variety to the exercise program, and increases adherence. (See 'Strength training: Safety and benefits' below.)
Role of the primary care provider — Most youth visit their primary care clinician at least once per year. Thus, the health care system provides a promising opportunity to promote physical activity in youth. Because of the focus on prevention services during annual visits, primary care providers are in a unique position to promote physical activity. Primary care providers can reassure their young patients and their parents that, with proper supervision and equipment and realistic expectations, strength-training programs designed for children and adolescents are safe and effective.
Overall, the primary care clinician has several roles in promoting physical fitness for their young patients:
●Encouraging daily physical activity in all children and youth and, for those who are interested, promoting a well-rounded general conditioning program to improve or maintain all of the components of physical fitness
●Helping parents determine the readiness of their child to participate in organized sports or a strength-training program (see 'Readiness to participate' below)
●Performing the pre-participation examination (see "Sports participation in children and adolescents: The preparticipation physical evaluation")
●Identifying contraindications and limitations to participation and defining modifications to participation and training
●Providing education and anticipatory guidance regarding nutrition, hydration, ergogenic aids, or performance-enhancing drugs such as anabolic steroids (see "Dietary recommendations for toddlers and preschool and school-age children" and "Nutritional and non-medication supplements permitted for performance enhancement" and "Prohibited non-hormonal performance-enhancing drugs in sport" and "Use of androgens and other hormones by athletes")
●Educating families on how to select experienced and qualified fitness or strength and conditioning specialists (see 'Choosing a coach' below)
●The National Prevention Strategy recommends that clinicians conduct physical activity assessments, provide counseling, and refer patients to allied health care or health and fitness professionals [61]
In addition, primary care providers can work with sports administrators and coaches in the community to share relevant information on injury prevention, injury assessment, rehabilitation, first aid, safety, and guidelines for returning to full activity following an injury. (See "Anterior cruciate ligament (ACL) injury prevention" and "Throwing injuries of the upper extremity: Treatment, follow-up care, and prevention" and "Concussion in children and adolescents: Management".)
STRENGTH TRAINING: SAFETY AND BENEFITS — Federal physical activity guidelines recommend muscle-strengthening activities on three or more days per week [10,12,62]. According to the National Youth Physical Activity and Nutrition Surveys, 51 percent of United States adolescents meet this objective [13,20].
Well-designed and supervised youth strength-training programs that follow recommended guidelines and safety precautions are accepted as safe and effective by the American Academy of Pediatrics (AAP) [2], American College of Sports Medicine (ACSM) [63], American Orthopaedic Society for Sports Medicine (AOSSM) [48], National Strength and Conditioning Association (NSCA) [49], United Kingdom Strength and Conditioning Association, and a 2014 International Consensus panel [51].
Misconceptions — Parents may have questions about the timing, safety, volume, risks, and benefits of strength training for their child. Despite the acceptance of strength training among health care and fitness professionals, there are several persistent misconceptions about its safety and benefits. These misconceptions are addressed below; they include [64-66]:
●Strength training is unsafe and stunts growth (see 'Safety' below)
●Strength training does not improve performance or reduce the risk of injury in children and adolescents (see 'Performance' below and 'Injury prevention' below)
●Strength training does not increase strength in children because they do not have enough testosterone (see 'Strength' below)
●Strength training is only for youth who compete in sports (see 'Other effects' below)
Safety — Reports of weight training from the 1970s and 1980s highlighted the potential for injury to growth plates and led to the misperception that strength training was not safe for youth [67]. However, improper training loads and lifting techniques, and poor supervision, contributed to most of the injuries reported in the literature at that time. Two reports using data from injury surveillance systems for weight training-related injuries from 1990 to 2007 [68] and from 2003 to 2005 [69,70] found that child injuries during weightlifting most often involved the hands and feet and were due to accidents, such as dropping weights. Thus, the majority of injuries are preventable with proper supervision and compliance with safety guidelines.
Mature, responsible coaching and supervision is the key to preventing strength training-related injuries in youth. Most physical activities entail some degree of risk for musculoskeletal injury. However, most injuries are not related exclusively to strength training and may occur in any activity or sport [71]. A well-supervised strength-training program poses no greater risk (and often less risk) to youth than does participation in many other recreational activities or sports [2,49,67]. A review of strength training programs in schools found no evidence of a higher prevalence of injury due to strength training when following a well-designed strength program [71].
Strength training poses a small risk of injury to the skeleton and soft tissues. The traditional concern in children is the potential for damage to the epiphyseal (growth) plate. However, an appropriate frequency of strength training using recommended loads, sets, and repetitions typically does not impose excessive stress on the physes and does not impair growth. Prolonged periods of repetitive impact activities, as seen in gymnastics or tumbling in cheerleading or with high volumes of endurance training, pose a greater risk of epiphyseal injury [48].
The risk of growth plate injury is minimal if children are taught correct principles of strength training and a gradual and appropriate progression of load is applied under the supervision of competent adults [48,49,72,73]. The case reports of epiphyseal plate fractures occurring during strength training have been attributed to misuse of equipment, improper lifting technique, lifting inappropriately heavy weight, or training in unsupervised settings [48,49]. (See 'Principles of training' below.)
Repetitive soft tissue injuries and injuries to the lower back are additional concerns for children participating in strength training. Overuse injuries result from repetitive microtrauma to structures that do not have the strength to withstand continual or repetitive forces of activity. The prevalence of overuse injuries is difficult to determine since they may not result in emergency department or clinician visits. The likelihood of such injuries may be increased by emphasizing sport-specific skills rather than overall fitness [50]. Injuries to the lower back are often a result of using unsafe training devices, improper lifting technique, or lifting inappropriately heavy weight.
With appropriate supervision, strength training may have a favorable influence on bone growth and development during childhood and adolescence [49,51,74]. Evidence that strength training in a controlled environment affects the growth of young participants is lacking [75-77].
Strength — For a strength-training program to be effective, the gain in strength must surpass that which is expected based on normal growth and maturation [66]. Such gains have been noted in children following relatively short periods (8 to 12 weeks) of a well-designed strength-training program. Strength gains of 30 to 50 percent have been reported in comparative trials [78-83].
Children and adolescents participating in a well-designed strength-training program make similar relative gains in strength, although adolescents make greater absolute gains [72]. The difference between the response to strength training in children and adolescents may be related to differences in circulating androgen levels, but other factors appear to contribute [80,84,85].
●In adolescents – The ability of strength training to increase strength in adolescents is well established [86]. Increases in strength in adolescents are due to the combined effects of neural adaptations and increases in muscle mass (hypertrophy) [66,87]. A 2018 meta-analysis of studies of resistance training in females between 8 and 18 years found a dearth of evidence, particularly when compared with studies of male youth, but reported that such training is effective, more so among older females [88].
●In children – Multiple meta-analyses provide evidence that strength gains are possible in children [85,88-90]. The benefits of strength training are not sex-specific: girls and boys both benefit from strength training. The training-induced strength gains observed in children are due to neural adaptations rather than hypertrophy [50,80,81,84]. The focus of strength training during pre-pubescence should be on neuromuscular development (ie, quality of movement) [71].
Strength training in children likely improves the coordinated recruitment of motor units, increases the number of motor units recruited, and improves the firing rate or firing pattern of activated motor neurons [84]. Improvements in strength also have been attributed to improved coordination [91]. Increased neural response and improved coordination may facilitate injury prevention in other sports and activities of daily living [92]. (See 'Injury prevention' below.)
As muscular strength is an essential component of motor skill performance, incorporating strength training into an activity or training program for a boy or girl can build competence and confidence when participating in various physical activities. This may have important long-term implications for health and for developing and maintaining physical fitness [51].
Although hypertrophy is not a typical response to strength training in children, there is some evidence that it may occur [93]. Further research using longer training periods, higher training intensities, and more precise measurement techniques may be necessary to demonstrate the potential for hypertrophy in children [49].
Performance — The overall performance benefits from a strength-training program vary depending on the quantity and quality of training, level of competition, type of sport (eg, contact or noncontact), and the skill level of the participant. Performance in a specific sport is affected by many variables. When assessing the impact of strength training on performance, it is important to distinguish among sport performance, performance on motor skill tests, and athletic ability. Improved strength does not necessarily improve sport-specific performance, although it often does, particularly as athletes reach adolescence [90]. Following participation in a strength-training program, improvements in motor skills (eg, agility, height of vertical jump, sprint speed) may be more noticeable than improvement in performance [73,94-98]. Certain resistance exercises that more closely approximate the movements involved in specific sports may serve as useful adjuncts to traditional strength training and enhance the transfer of strength gains to sports performance.
Regardless of the potential benefits of strength training, children and adolescents should participate in an overall conditioning program that develops all the components of health- and sports-related physical fitness and sport-specific skills as part of an individual or team training program. Improvements in physical fitness (including strength) increase a youth's ability to participate in a variety of activities, including work, play, recreation, and sport. (See 'Physical activity' above.)
One strategy used by some coaches to optimize performance and fitness is concurrent training of muscular strength and cardiorespiratory fitness [99]. Concurrent training is efficient and may enhance both strength and endurance; however, concurrent training may produce inferior improvements in each attribute compared with training strength and endurance independently [100]. Interference between the two modes of training is likely due to differences in metabolic signaling and the resulting muscle adaptations: increased hypertrophy versus increased capillarization and oxidative capacity. Such interference effects may be minimized or eliminated if strength and endurance training are performed on alternate days [101].
Of note, our understanding of the effects of physical training comes predominately from research in adults, the results of which may not apply to children, and concurrent training may be an example. In a meta-analysis of 15 studies of limited quality, concurrent training was found to be slightly better than endurance or strength training alone for improving selected measures of athletic performance and fitness in children and adolescents [99]. Among youth, concurrent training lends itself to participation in a more well-rounded physical training program than does isolated training. In addition, by reducing the total time spent engaged in endurance and strength training, concurrent training may increase the time available for recovery and the development of sport-specific skills. Reduced training volume and increased recovery time may also reduce the risk of injury.
Injury prevention — The risk of injury increases with participation in sport. However, children and adolescents who follow age-appropriate strength-training recommendations have a relatively low risk of injury while performing resistance exercises [73,77]. In addition, adolescents who take part regularly in a well-designed strength-training program appear to be at lower risk of acute and overuse injuries when participating in other sports [102]. Participation in a general overall conditioning program may also reduce the risk or lessen the severity of sports-related injuries and likely reduces the risk of injury during non-sport and non-leisure physical activities [49,57,58,72,103-106].
Children and adolescents can be encouraged to participate in a conditioning program prior to or in the early stages of a sports program. An overall conditioning program that includes strength training may help to prepare unconditioned youth for the demands of sports practice and competition [51,107,108]. Such training increases the strength of the muscles, tendons, and ligaments and increases joint stability. Resistance exercises that develop strength through a full functional range of motion also maintain mobility [5,48,49,72]. Each of these effects potentially contributes to a reduced risk of injury [109].
A small number of well-performed randomized trials support the contention that participation in a well-designed and properly implemented neuromuscular training program that includes appropriate resistance exercises can reduce the risk of injury among adolescents. The effectiveness of the former intervention is seen in a cluster-randomized trial, involving 230 Swedish football (soccer) clubs and 4564 female players ranging in age from 12 to 17, where players whose teams participated in a neuromuscular training program (intervention group) sustained seven anterior cruciate ligament (ACL) tears compared with 14 among players whose teams did not (control group) [110]. ACL injury prevention is discussed in detail separately. (See "Anterior cruciate ligament (ACL) injury prevention".)
The effectiveness of a robust strength-training program is seen in a study of 52 elite Tunisian male soccer players, ages 13 and 14, who were randomly assigned to soccer training plus regular progressive strength training (two to three 90-minute sessions weekly, including barbell squats and bench press) or to standard training only [111]. All other aspects of training and match play were identical. Players in the strength-training group sustained four significant injuries (effects lasted longer than three days) over seven months (including one ankle sprain and no acute non-contact muscle injuries) compared with 13 significant injuries among non-participating athletes (including three ankle sprains and six acute non-contact muscle strains).
Weight management — Including strength training as part of an exercise program can help with weight management or improved body composition [27,28]. Increases in muscular strength and endurance can improve physical function and the ability to participate in other forms of physical activity, recreation, exercise, and sports. Long-term effects include increased energy expenditure, reduced body fat, and increased lean muscle mass. Research in adults supporting the effectiveness of resistance training as a tool for combating obesity and improving body composition is discussed separately. (See "Strength training for health in adults: Terminology, principles, benefits, and risks", section on 'Endocrine-metabolic'.)
Other effects — Participation in a well-supervised and structured strength-training program may have benefits beyond increased strength and performance for the athlete and non-athlete alike (table 1) [3].
Participation in a conditioning program that includes strength training can help children to learn about their bodies [65]. It may change their attitudes toward physical conditioning, physical fitness, physical education, and lifelong exercise [15]. Strength training may be particularly beneficial for overweight/obese children who may not be able to tolerate prolonged periods of aerobic exercise [112].
STRENGTH-TRAINING PROGRAMS — Training guidelines and recommendations for developing and implementing strength-training programs for youth have been published in the fitness literature [3,49-51,65,113,114]. Recommendations for warm-up and cool-down, overload, and progression of exercises are summarized in the table (table 2) and discussed in greater detail below. (See 'Principles of training' below.)
General guidelines — The goal of a youth strength-training program is to increase muscular strength and endurance while being exposed to a variety of fun, safe, effective, and age- and developmentally appropriate training methods, sports, and activities as part of a well-rounded fitness program. The development of strength should complement, and not neglect, other components of physical fitness and well-being.
Team sports tend to result in less specialization, while individual sports tend to have higher levels of specialization as well as higher training volumes. Athletes also tend to specialize at a younger age when involved in individual sports as opposed to team sports [115]. However, there is greater development and transfer of motor skills when youth participate in a variety of activities and sports. Despite the common belief that early focus on a single sport is advantageous to achieving a high level of performance, a single-sport emphasis may be detrimental to the overall physical development of the child and increase the risk of injuries [115]. In addition, youth who participate in a single individual sport have higher training volumes and greater rates of overuse injuries compared with youth involved in a single team sport. Youth (and their parents) should be encouraged to pursue a reasonable variety of participation in activities, sports, recreation, and training.
Serious injury may occur if proper guidelines are not followed. Close attention should be given to any related pain or injury. Normal muscle soreness must be distinguished from pain. Pain during an exercise precludes continuation of that exercise. Pain following an exercise, including the following day, precludes performing the exercise during the next exercise session [5]. Symptoms that persist longer than two days merit medical evaluation.
Additional general guidelines for a safe and successful program include [3,50,51,65,114,116]:
●Qualified adults should provide supervision and instruction at all times. Adult spotters should actively assist the participant when necessary.
●Participants should wear appropriate clothing and footwear.
●Strength-training equipment should fit the participant.
●The focus should be on safe training, proper technique (eg, controlled movements and proper breathing), and individual improvement rather than on competition and the amount of resistance.
●Progress should be monitored and reviewed regularly.
●The program should be varied over time to prevent boredom and burnout.
●To avoid injury during periods of accelerated growth (eg, adolescent growth spurt), the intensity and total volume of the training program, the athlete's response to training, and reports of discomfort and pain should be closely monitored.
Readiness to participate — Readiness to participate in strength training is defined relative to the demands of the sport and the physical, cognitive, and social maturity of the child. Children and adolescents should begin strength training only if they perceive it to be worthwhile and should continue strength training only if it continues to be enjoyable, satisfying, meaningful, and challenging [5]. Children and parents must clearly understand that the objectives of strength training are increased muscular strength and endurance rather than increased muscle size.
There is no minimal age requirement for participation in strength training, but each participant should have the maturity to accept and follow directions (usually around seven or eight years). If a child is capable of participating in an organized youth sport, he or she is capable of participating in some form of program designed to condition the body to meet the physical demands imposed by the sport [114].
The pediatric or sports medicine clinician can help parents determine the readiness of their child to participate in organized sports or a strength-training program. The physical, cognitive, and social demands of the activity or sport must be considered. In addition, family values regarding sport, including risk tolerance, physical demands, and psychosocial development, should be considered. In addition to conversations with clinicians and coaches, the Aspen Institute's Healthy Sport Index may help youth and their families select a sport that conforms with their goals [117]. Physical maturity is a major factor in determining a child's ability to withstand the stresses of sports participation or athletic training and conditioning [118].
Preparticipation examination — Some organizations suggest an examination by a clinician knowledgeable in sports medicine before participation in strength training [2,5,48]. Others suggest that for apparently healthy youth, a medical examination is desirable but not absolutely necessary before participation in a strength-training program [49]. We prefer that a specific preparticipation examination be performed. Such an examination offers an opportunity not only to assess the health of the child but also to provide guidance, set reasonable expectations, dispel myths, and answer general questions about the benefits, risks, and proper approach to strength training in children. There is general agreement that preparticipation examination is mandatory for children with known or suspected conditions that may exclude or limit participation or require treatment (eg, hypertension). (See "Sports participation in children and adolescents: The preparticipation physical evaluation".)
A preparticipation examination can be an important component of injury prevention, especially when undiagnosed or incompletely rehabilitated injuries are identified and treated [114]. It also provides an opportunity for the clinician to ask about the participant's health behaviors and to educate the participant and parents (table 3). The American Academy of Pediatrics (AAP) suggests that youth with uncontrolled hypertension, seizure disorders, or a history of anthracycline-based chemotherapy for childhood cancer should undergo additional evaluation and/or treatment before participation [2].
Contraindications and precautions — The AAP suggests that youth with cardiomyopathy (particularly hypertrophic cardiomyopathy) should be counseled against weight training since they are at risk for worsening ventricular hypertrophy and restrictive cardiomyopathy or hemodynamic decompensation secondary to an acute increase in pulmonary hypertension [2]. The AAP also suggests that youth with moderate to severe pulmonary hypertension refrain from strenuous weight training because they are at risk for acute decompensation with a sudden change in hemodynamics [119]. (See "Pulmonary hypertension in children: Management and prognosis", section on 'Long-term health maintenance' and "Hypertrophic cardiomyopathy in children: Management and prognosis", section on 'Recreational exercise and competitive sports participation'.)
Choosing a coach — Choosing a coach is an important parental responsibility [5]. Coaches and parents must have a common goal of the overall development of the child and the adoption of lifelong exercise behaviors.
Coaches, supervisors, or trainers should have adequate education and experience to apply scientific knowledge and principles to the development and progression of a training program for a given participant [51,67]. They should provide the participant instruction regarding exercise technique, use of equipment, weight-room etiquette, training guidelines, and safety. The primary focus of the program should be learning and mastering new motor skills and movements used in strength training.
Parents in the United States can be referred to the websites of the American College of Sports Medicine (ACSM) or National Strength and Conditioning Association (NSCA; www.nsca.com/Home) for help in finding a qualified professional to lead a strength-training program. In addition, some public schools include strength training as part of their physical education curriculum or as an after-school program. Some local fitness centers or community recreation centers include strength-training programs for youth.
Before the child begins a strength-training program, the parent and child should discuss why he or she wants to train. Parents and their child should agree on the purpose of having a coach, the training objectives, and the criteria for continuing.
Equipment — Strength-training equipment should fit the participant. Young or small children who use equipment designed for use by adults will not have proper body alignment and support, making the exercise less effective and potentially unsafe. Barbells as light as 4.5 kg (10 pounds) and bumper plates as light as 2.25 kg (5 pounds) are available and are useful for learning technique.
The size, seating, and weight increments on many strength-training machines are designed for adult use and are too large for most children and many adolescents. Alternative methods of applying resistance are discussed below. (See 'Overload' below.)
Principles of training — There are eight principles of training that are applied to conditioning programs (table 2):
●Individualization
●Warm-up and cool-down
●Specificity
●Overload
●Adaptation
●Progression
●Maintenance
●Reversal
Individualization — Each participant has unique goals, objectives, needs, abilities, limitations, resources, and experiences that affect his or her participation, performance, and improvement in an activity or sport. Clinicians, parents, coaches, teachers, and program directors can help each participant to meet his or her unique needs effectively and safely. To increase adherence and compliance, the child should be actively involved in the selection and development of an exercise program that meets his or her personal, physical, and social needs.
Warm-up/cool-down — Every bout of exercise should begin with a 5- to 10-minute active warm-up that includes dynamic mobility exercises, aerobic exercise, and repetitions of light resistance to prepare the body for the specific activity that will be forthcoming. Warm-up activities stimulate metabolism and increase body temperature and blood flow to active musculature.
Each exercise session should be followed by a 10- to 15-minute active cool-down period that includes light aerobic exercise and stretching. Cool-down activities maintain blood flow to active muscles during recovery and enhance the quality and effectiveness of the recovery period.
Specificity — The training stimulus (overload) must be effectively applied to a specific physiological system for the expected neuromuscular adaptations to take place. Training adaptations are specific to the type and mode of training and the total overload.
A well-rounded general strength-training program can meet the needs of most youth. Such a program can increase muscular strength and endurance, speed, and power. Athletic performance, on the other hand, is optimized by matching the demands of the sport with the training program: training the appropriate metabolic systems and duplicating sport-specific joint velocities and angular movements.
Overload — For neuromuscular adaptation (training effect) to occur, the training stimulus must be greater than that to which the participant is normally accustomed. A strength-training overload is applied through the choice and order of exercises, load, sets, repetitions, rest periods, and frequency of training. The load can be applied through various forms of resistance (eg, free weights, machines, body weight, elastic bands). The type of load may influence the benefit of strength training. In a meta-analysis, anisometric (also called isotonic) training programs had a greater effect than isometric training programs, but the effect sizes did not reach statistical significance [85].
●Choice and order of exercises – When choosing exercises, it is important that the child fits the equipment and that the skills and technique to perform the exercise are properly taught. Six to eight exercises total that involve all the major muscle groups (chest, shoulders, back, arms, legs, abdomen, lower back) should be selected with appropriate balance across joints (ie, flexors and extensors) as well as between upper- and lower-body muscle groups.
Participants should be encouraged to train all the major muscle groups rather than a limited number (eg, chest and arms). Because of the potential for lower back injuries during strength training, exercises that strengthen the core (ie, abdomen and lower back) should be included in all training programs [3,5,50]. (See 'Injury prevention' above.)
Most exercises should be performed through the full, functional range of motion to properly develop strength and prevent loss of mobility [5,48,49,72]. Exceptions include exercises that place undue stress on joint capsules or have extreme ranges of motion, such as bar dips and supine dumbbell flies. These exercises should be performed only to the point of the upper arm being parallel to the ground (picture 9 and picture 10).
Common practice is to perform multijoint exercises before single-joint exercises, complex movements before simple movements, and large muscle groups before small muscle groups. Performing exercise in this order helps to prevent training plateaus, increase training efficiency, and decrease injury potential. In some cases, it may be beneficial to perform exercises that focus on movement patterns and involvement of the entire kinetic chain as opposed to isolating single muscle groups.
●Load – Load is the measurable amount of resistance. Load should be selected so that the predetermined number of sets and repetitions can be completed with some fatigue (not failure). Fatigue is the participant's perception that the repetitions are too hard or that form and technique cannot be maintained. Failure is the inability to complete the repetition.
Strength training should begin with lighter loads that allow more repetitions and progress to the use of heavier loads as strength and technique are developed. When starting a strength-training program, the participant can select loads that allow the completion of at least 10 repetitions without excessive fatigue or failure. If the beginning participant fails to complete at least 10 repetitions per set with a given weight, the weight is too heavy and should be reduced [3,5].
When learning new movements, no-load repetitions can be used to develop balance and control. Load can be increased gradually as the movement is learned, but increments in load should not exceed the participant's ability to maintain balance, control, and proper technique.
Opinions vary on whether youth should lift maximal weights. Some organizations recommend that strength-training programs for children and adolescents exclude lifting maximal amounts until they attain physical and skeletal maturity [2,114]. It is reasonable to use maximal lifts to evaluate the effectiveness of a strength-training program when the maximal lifts are supervised and performed correctly following an adequate, gradual progression of loading [120]. However, there is no support for the continuous use of maximum-resistance training in youth. Instead of continually lifting maximum loads, participants should be encouraged to use submaximal loads to develop form and technique in a variety of exercises.
Strength-training programs for children should not rely on one form of resistance exercise (eg, free weights) [49,114]. Programs should be designed to include a variety of physical activities and training methods that develop muscular strength, rather than "specializing" in one strength-training method. Different methods of applying a resistance, such as use of body weight, free weights, weight machines, rubber tubing, and medicine balls can be used in strength-training programs for youth.
•Body weight (eg, pull-ups, bar dips, or push-ups (picture 11)) should not be used as a form of resistance when working with sedentary or obese children who lack the strength to safely and successfully perform the exercise.
•Free weights (picture 2) are a viable alternative to weight machines when child-size equipment is not available or when working with large children who have difficulty getting in and out of machines. Light-weight or unloaded bars should be used initially to develop proper technique and movement patterns.
•Rubber tubing or other forms of resistance bands can be used by many children who are not ready to use free weights or machines. Since the resistance increases further into the range of motion, children should be encouraged to move through a full range of motion while maintaining proper body alignment.
•Medicine balls of various sizes can be used to develop upper-body and abdominal strength.
●Sets – A set is the completion of a given number of repetitions. Single-set protocols are often completed in the first several weeks of training when skill development and conditioning is low. Most youth are encouraged to begin a strength-training program using one to two sets.
●Repetitions – Repetition is the number of times the load is lifted in a given set. Once movement patterns are established, it is recommended that youth perform sets using loads that permit 5 to 15 repetitions without failure and with good form [49].
●Rest periods – A rest period is the amount of rest between sets or between exercise sessions. The length of rest periods between sets contributes to the overall overload since shorter rest periods decrease the recovery of energy-producing metabolic pathways and affect performance on subsequent sets.
One to three minutes of rest between sets is generally adequate; shorter rest periods are used to emphasize hypertrophy, and longer rest periods to maximize strength. Most youth have difficulty resting more than one to two minutes between sets.
●Frequency of training – Muscle groups should be given at least 24 hours of rest between exercise sessions. Thus, strength training in youth should be limited to two to three nonconsecutive days per week. Older adolescents who are highly motivated can strength-train four days per week, provided that major muscle groups are not trained on consecutive days. In a meta-analysis of resistance training in children and adolescents, increased frequency of training was associated with increased strength gains [85].
Adaptation — Adaptation is the primary reason for engaging in any activity, exercise, or conditioning program. The neuromuscular adaptations to strength training in youth include increased numbers and coordination of recruited motor units and improved firing rate or firing pattern of activated motor neurons [84]. Initial improvements in strength from resistance training in pre-adolescent boys and girls result from neural adaptation. However, depending on the trainee’s stage of development, adolescents may experience an increase in muscle mass. (See 'Strength' above.)
In addition, regular physical activity, including a well-designed strength-training program, helps to increase bone mass. (See "Bone health and calcium requirements in adolescents", section on 'Physical activity'.)
Progression — The progression of an exercise program is critical to safely and effectively meet the individual's goals and objectives. As strength increases, the original absolute resistance represents a lower workload relative to capacity. The overload must be increased to provide an effective stimulus for adaptation to continue.
The overload can be changed by increasing the resistance, the number of sets or repetitions, the frequency of training, or the number of exercises performed for each muscle group.
●Before increasing the number of sets or resistance, participants should be able to demonstrate proper technique.
●Resistance can be increased when the desired number of repetitions can be performed, when 20 repetitions become "easy," or when the participant can complete three sets of 20 repetitions [5,50]. Resistance can be increased in increments of 5 to 10 percent.
●The addition of exercises for each muscle group adds variety to a program, emphasizes the overall objective of conditioning, and introduces new movement patterns and motor skills. Addition of new exercises should include the use of single-joint and multijoint exercises. Multijoint exercises are beneficial for the development of neuromuscular coordination and skill technique and require more balance and stabilization [49,50]. Participants should not be allowed to perform more complex exercises until less complex exercises are mastered [5,49].
Progression to performing two to three exercises per muscle group for one to three sets of 10 to 15 repetitions, performed three days per week, or three to four sets of six to eight repetitions, has been recommended [5,50,72].
Maintenance — The maintenance phase is the longest portion of any conditioning program. Eventually, the participant is satisfied with the adaptations, training effect, and new level of physical fitness, health, or performance, and increases in overload (progression) are no longer needed. Less total overload is necessary to maintain adaptations than to achieve the desired outcome. Duration of training can influence the benefit of strength training, since training interventions of longer duration are more beneficial than similar training programs of shorter duration [85].
Reversal — Youth participation in sports and conditioning programs is often spontaneous and sporadic. It is likely, therefore, that many youth will undergo periods of reduced training and activity. Following a significant reduction or cessation of strength training, strength and other related adaptations regress to pretraining levels [81,121]. This phenomenon is often referred to as "detraining" and occurs in children as well as adults.
In children, the effects of detraining are confounded by the concomitant growth-related increases in strength. The precise nature of the detraining response in children and adolescents remains uncertain. However, changes in neuromuscular function probably play a significant role in the observed changes in strength or motor performance.
Olympic-style lifting — The snatch (picture 4) and the clean-and-jerk (picture 5) are the two lifts included in the sport of weightlifting (often referred to as Olympic weightlifting). In the snatch, a barbell is lifted from the ground to an arm's-length position overhead in one continuous movement. In the clean-and-jerk, the barbell is lifted from the ground to the shoulder and then to an arm's-length position overhead in a two-part movement. Both lifts are performed rapidly and require power and expert technique.
Olympic-style weightlifting movements can be used as an effective training modality to improve strength, power, and coordination [50,122-125]. The AAP suggests that children and adolescents avoid competitive weightlifting and power lifting until they reach physical and skeletal maturity [2]. Others suggest that such lifts are appropriate for youth who demonstrate the maturity and desire to learn proper technique before using significant amounts of weight [50,122,124,126]. The time and effort required to learn and practice these techniques can vary among participants.
With proper training and technique, weightlifting is safer than many other sports in which teenagers regularly participate [122,124]. The forces to which children are exposed in other sports and activities are often greater in duration and magnitude and typically occur in uncontrolled settings. The snatch and the clean-and-jerk are complex movements and require knowledgeable coaching and supervision. When technical mastery is emphasized, the risk of injury is decreased.
Olympic-style lifts should not be attempted without proper training and supervision; this point cannot be overemphasized. The training program should include other lifts and forms of conditioning to provide overall training. The techniques for the snatch and clean-and-jerk should be learned using a wooden pole, polyvinylchloride (PVC) pipe, or light weight-training bar. Resistance should not be increased until the child has developed the necessary neuromuscular coordination and skill to perform the lift correctly. Light to moderate intensities (less than 75 percent of the one-repetition maximum) are recommended for youth.
SUMMARY AND RECOMMENDATIONS
●Goals of participation – Children should be encouraged to participate in regular physical activity in order to establish good health habits at an early age. A panel convened by the United States Centers for Disease Control and Prevention (CDC) recommends that school-age children participate in at least 60 minutes per day of moderate to vigorous physical activity (MVPA). (See 'Physical activity' above.)
Organized physical activity and sports programs should contribute to the overall development of the child and the adoption of lifelong exercise behaviors. (See 'Goals' above.)
●Strength training is safe and effective – Well-designed and properly supervised strength-training programs that follow recommended guidelines and precautions are safe and effective in producing strength gains (and other benefits (table 1)) for children and adolescents (both boys and girls). Strength-training programs for children and adolescents should be a part of an overall well-rounded fitness program that complements other components of physical fitness and well-being. (See 'Strength training: Safety and benefits' above and 'Strength-training programs' above.)
●Readiness for strength training – Readiness to participate in strength training is defined relative to the demands of the sport and the physical, cognitive, and social maturity of the child. (See 'Readiness to participate' above.)
●Training principles – Children and adolescents who participate in strength-training programs should follow the guiding principles outlined in the text and following table (table 2). (See 'Principles of training' above.)
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