Table of Contents  

Pierce and Stone: Children and sport – how hard should children be trained?

Introduction

Resistance training is a general term dealing with regular exercise used for improving strength and strength-related characteristics such as muscle hypertrophy, maximum rate of force development (RFD), power, strength–endurance or speed. Resistance training can be viewed from the aspect of the type of equipment used or the goal being sought. The training can include body weight exercises or use of resistance-producing devices such as stretch bands, various machines, free weights (weight training) or, more commonly, combinations of this equipment. Resistance training can be part of an overall programme for health or for sport, or it may stand alone. From a sport perspective, resistance training also includes the competitive facets of bodybuilding, powerlifting and weightlifting.

Because the number of participants engaging in strength training, a form of resistance training, has been increasing among all levels and ages of the population,1 it becomes increasingly imperative to understand the potential consequences of the training process, particularly when those consequences concern more vulnerable or fragile sectors of the population. It should be realized that strength is more than simply ‘how much can you lift’; rather it is a vehicle for impulse, RFD, power, some aspects of endurance and sport performance as it has been shown numerous times in both cross-sectional25 and longitudinal studies5,6 that these factors are related to maximum strength and can be positively altered with strength training. Therefore, our purpose is to briefly review the potential outcomes of the resistance training process as it affects children and adolescents, particularly as it relates to training for sports.

Controversy 1 – efficacy

It is apparent that considerable controversy and lack of understanding have and still currently surround children and resistance training, especially as it concerns training for sport. This controversy has also been previously noted.711 Often the controversy originates from opinion, or a sort of consensus practice (sometimes called a ‘rich tradition’),12,13 rather than in demonstrable data. This controversy can be looked at in two parts. First, does resistance training have benefits for children, does it produce substantial and worthwhile alterations in structure, strength and power among children (aged up to approximately 10 years – Tanner stages I and II), early adolescents (aged approximately 10–13 years – Tanner stages II and IV) and adolescents (aged approximately 14–18 years – Tanner stage V)? Second, what are the safety and injury considerations for children, adolescents and resistance training?

To understand the issue of efficacy, a discussion of the ‘trigger hypothesis’ is required. The triggering effect for improved performance (including strength development) ‘results from the modulate effects of hormones that initiate puberty and influence functional development and ensuing organic adaptations’ prior to this ‘critical period’ few or no effects from physical conditioning will transpire.14 The idea of a mechanistic ‘trigger’ indicates that little or no alteration in performance, physical composition or strength-based physiology is likely to take place until puberty or beyond. This misconception has often been represented in popularized models as representing ‘windows of opportunity’ around puberty. Although there is some support for this hypothesis dealing with the development of aerobic capabilities among pre-pubescent children and adolescents,15,16 there are a number reasons for substantial modification of this hypothesis in terms of resistance training.17

The first basis for modification deals with careful and systematic observation. For example, children beginning gymnastics programmes typically cannot perform simple tumbling or body weight-supported exercises. Within a few weeks or months they can attain reasonable proficiency. This can occur only with some improvement in strength; thus, gymnastic training serves as a form of resistance training.18,19 Young female gymnasts have shown substantial enhancements in fitness coupled with continued increases in performance levels in probably the oldest and consistent talent identification programme in the USA. The Talent Opportunity Program has been operating since 1993 and has annually demonstrated increases in strength fitness among the participants as they age and as more importance is placed on strength–power development.2023

Evidence also indicates that alterations in hormones or increases lean body mass (LBM) occurring with puberty occur later than maturation aspects of the nervous system. Because the nervous system is directly associated with training-induced alterations in force production capabilities (e.g. maximum strength etc.) there is reason to suspect that nervous system adaptations to resistance training could also affect positive performance adaptations among children, including pre-pubescents.

Furthermore, some degree of hypertrophy can occur without marked hormonal (e.g. testosterone) influence. Alterations in muscle cross-sectional area (CSA) can often be observed among women taking up resistance training. Thus, theoretically there is a logical expectation for some degree of hypertrophy in children. This is reinforced, at least indirectly, by age/training-related differences noted in body composition measurements of highly trained female gymnasts.2426

Additionally, substantial research has shown that early and late adolescents and children can increase strength, power and endurance, often markedly, and make substantial physical alterations as a result of resistance training. Among this evidence are several studies and reviews of the literature2736 including meta-analyses3739 involving children of various ages and the effects of resistance training. These reviews indicate that:

  • In boys (aged < 13 years) and girls (aged < 12 years) there can be a clearly increased level of strength and strength-endurance as a result of resistance training, and there appears to be only a minor sex (male to female) effect on absolute or relative strength gains. In adolescents (aged up to 18 years) there can be increased strength, power and strength–endurance, and the absolute gains do reflect substantial sex differences.

  • Although resistance training can result in a degree of hypertrophy in children, a larger degree of hypertrophy can be expected among early and late adolescents. This outcome is probably mediated by hormonal and other maturation effects that accompany growth. In this context, alterations in body composition, such as increased LBM and decreased fat/fat content, can also occur as a result of resistance training, with early and late adolescents generally responding to a greater degree.

  • Isometric and isokinetic programmes do not appear to produce the same degree of hypertrophy or strength gain as other forms of resistance training such as use of variable resistance machines and free weights.

  • The alterations in body composition, strength, power and hypertrophy are a function of sex (in older children), the training mode (isometric, free weights, etc.) and method (e.g. exercise selection, training intensity, training volume), and the experimental design. The evidence strongly indicates that the most effective programmes last more than 8 weeks and involve multiple sets per exercises.

  • Resistance training of sufficient intensity can beneficially alter metabolic function.

As noted, the primary mechanism underlying gains in children for beneficial alterations in maximum strength and related characteristics, such as RFD and power, appears to be primarily neural, as there is less demonstrable hypertrophy. However, among adolescents, particularly late adolescents, the effects of strength training appear to result from increased CSA and neural mechanisms.4042

Controversy 2 – injury potential

There is little doubt that both long-term observation and recent research indicate that children and adolescents can benefit from resistance training; however, injury potential has been at the centre of controversy for some time, especially as it concerns sport. In the authors’ experience, and that of others,10,11 the controversy is largely founded on opinion and misinterpretation of information rather than solid evidence. Indeed, it is not uncommon to find websites that include incorrect statements, for example:

The goal of strength training is not to bulk up. It should not be confused with weight lifting, bodybuilding, and powerlifting, which are not recommended for kids and teens. In these sports, people train with very heavy weights and participate in modeling and lifting competitions. Kids and teens who do those sports can risk injuring their growing bones, muscles, and joints.

KidsHealth43

Too often, well-intentioned individuals who work with children in medical or sports and fitness settings erroneously believe that resistance training, and in particular weightlifting and powerlifting, are dangerous activities, particularly for children.44 Within the last 20 years the authors have had numerous discussions/presentations with parents, coaches, teachers, physicians etc., concerning the efficacy and safety of resistance training, and in particular the sport of weightlifting. These discussions have been in both formal settings21,4550 as well as informal settings. We have been consistently astounded at the misinformation that has persisted over this time period despite the evidence that is accumulating as to the many benefits of resistance training for children and adolescents.

Historically, resistance training, particularly strength training for competitive sport, has been generally regarded as ‘unsafe’ for children.5153 This misconception has stemmed from poorly designed and misinterpreted data from the 1960s and 1970s.54 These misconceptions and misinterpretations have had a serious negative impact for over 40 years. These papers concluded that resistance training should be used with extreme caution and that weightlifting and powerlifting are associated with a high injury rate and should be avoided by pre-adolescents. Unfortunately, these papers were largely based on the rare occurrence of epiphyseal growth plate injuries at any age and the erroneous idea that strength training might ‘stunt growth’.29,55,56

For a better understanding of how this controversy came about, a brief history of the medical/scientific efforts to address resistance training including resistance training for competitive sport is in order. In 1983, the American Academy of Pediatrics (AAP) produced a position statement that has had a substantial and serious negative impact for more than 30 years.51 Much of the logic and reasoning behind this position was based on injuries to the epiphysis55,57 and musculoskeletal system maturation rates and levels. The position paper concluded that resistance training should be used with extreme caution and that weightlifting has a high injury rate and should be avoided by preadolescents. Sewall and Micheli58 agreed with these statements, recommending that any resistive training for preadolescents should be controlled and with slow movement speed, and that weightlifting competition should not take place until after skeletal maturation is attained. In contrast, Micheli59 later stated that there was little scientific evidence regarding injury potential of preadolescents involved in resistance training and that the potential for growth plate injury may actually be less in the pre-pubescent than in the pubescent because the growth plate is actually much stronger and more resistant to shear stress in younger children than in adolescents. Furthermore, a substantial number of studies and reviews of the literature have reported positive performance, beneficial physical and physiological adaptations in children and early and late adolescents, with no associated increased injury potential.7,28,33,34,60 A second position paper by the AAP recommended that ‘Unless good data becomes available that demonstrates safety, children and adolescents should avoid the practice of weight lifting, power lifting, and body building …’.52 This conclusion was again stated in a third position by the AAP in 2001 (recommendation 2).53

First, we must assume that the authors are actually referring to organized competitive sports, as the terms weightlifting, powerlifting and bodybuilding are misspelled, if referring to these competitive sports.61 The correct spelling is imperative as these sports and competitive activities are often confused with recreational or non-competitive activities. Again these statements are made with little or no supporting evidence and, apparently, an inaccurate understanding of the activities involved. Surprisingly, no specific literature dealing with any aspect of physiological biomechanics or medical concerns was cited that actually examined these competitive sports. However, several studies and reviews8,9,55,6265 and opinion papers8,9 were available in 2001. Notably, there is little or no evidence provided in the AAP statements5153 of contact with the international or national governing bodies of these sports, or their scientific committees, in order to gain further insights into the effects of resistance training and particularly the effects of these sports on children and adolescents.

Assuredly, substantial research and experiential data concerning youth weightlifting, in English or published or translated into English, have been available since at least the 1970s and 1980s.9,62,6570 Most studies and reviews do not support the AAP proscription of these sports.8,9,11,55,6270

Similar positions largely based on the same data as the AAP seem to have been adopted by other organizations. A position paper by the American College of Sports Medicine was supportive of weight training, but not with maximal weights,32 although the term ‘maximal weights’ was not well defined. This statement, by implication, would propose a position against resistance training as part of sports training or competitive weightlifting or powerlifting for children and adolescents up to the age of approximately 16 years (Tanner stage V). However, exhaustive literature reviews and position papers by the National Strength and Conditioning Association (NSCA)33 and the British Journal of Sports Medicine10 were developed and published in support of children’s resistance training programmes. One aspect addressed by these reviews is the appropriate supervision by trained professionals.

More recent literature reviews28 and updates71 have taken a somewhat less conservative nature. Although these updated papers generally support strength training among children and adolescents, it is less clear what methods and loading schemes would be deemed to be acceptable. Indeed, ‘maximal weights’ in training was generally proscribed. However, the term ‘maximal weights’ was not well defined, and by implication would seem to constitute a position against strength training as part of sport or competitive weightlifting training for children and adolescents until reaching 16 years old (Tanner stage V).

The 2008 AAP Policy Statement acknowledged that research on children participating in the sport of weightlifting resulted in few injuries as a result learning correct technique and having strict supervision.71 Interestingly enough, weightlifting was removed from the previous recommendation52,53 regarding activities preadolescents should avoid: ‘preadolescents and adolescents should avoid power lifting, body building, and maximal lifts until they reach physical and skeletal maturity’ (recommendation 2).71 However, they were hesitant to support competitive weightlifting for ‘children who are skeletally immature’ because of ‘limited research’ on prepubertal injury rates.71

The British Association of Sport and Exercise Sciences (BASES)28 has produced a document in which resistance training recommendations for various age/developmental levels (children, early and late adolescence) are made. Although BASES28 does make some very sound recommendations, it its recommendation on resistance training for competitive sports is not clear and it seems to warn against training for sport, including weightlifting and powerlifting for children and early adolescents.

By contrast, a number of reviews and studies of injury type and injury rates associated with strength training among both youth and adults indicate that injury rates and incidence are not excessive. Furthermore, injuries occur at smaller frequencies and are usually less serious than those associated with sports such as American football, basketball, gymnastics, football or rugby.55,72 Injuries are generally the result of poor technique, excessive loading, overly fatigued training, poorly designed equipment, unrestricted access to the equipment or, typically, lack of qualified supervision.72,73

Revision of the 2009 NSCA position stance,74 and a position stance by the Canadian Society for Exercise Physiology,75 indicated that weightlifting was considered to be a safe activity, and with appropriate planning and good coaching there is no reason why children cannot participate. In part, paucity of data has been an issue; however, alarmist responses by well-meaning physicians, educators and coaches has resulted in a disservice to weightlifting, the use of strength training as part of the training process for other sports and, most importantly, the potential development of children and adolescents. In particular, weightlifting is often condemned by the uninformed as being especially injurious. However, objective evidence indicates that resistance training, including the sport of weightlifting, is actually considerably safer than has been generally believed. This is especially true if training and competition are tailor made to be appropriate for the age group and appropriately supervised.7,9 Considering that evidence indicates that children and adolescents can physically, physiologically and psychologically benefit from strength training, and that strength training is a safe activity for these groups, then it follows to that we must continue to develop appropriate training guidelines that are appropriate for children and adolescents.10,11,74,75

Guidelines for training/coaching

When training adolescents, and particularly children, there are various concerns that must be addressed before beginning the training process.

An initial concern is whether or not the child is physically and psychologically prepared. From a psychological/emotional perspective it is important that children and adolescents be encouraged to participate in physical activity that challenges and provides enjoyment and satisfaction; especially for children, the tasks must be rewarding and ‘fun’. Promotion of self-improvement and satisfaction, along with good performances, can be provided through encouragement by the coaches/instructor. At the same time care should be taken in helping the children (and adolescents) deal with poor performances or not always reaching goals. This means that the development of realistic expectations and the realization that it often takes a considerable amount of time to learn new skills or change physiology/psychology (e.g. get fit) should be carefully explained to the participants by the coaches/instructors. The degree of encouragement by coaches and instructors to exceed previous goals must be weighed against potential negative effects on some young people, who may interpret encouragement as pressure. Often there is a fine line between ‘pressure’ and ‘encouragement’. Level of emotional and intellectual maturity is important to recognize in children (and anyone else) when initiating a training process. A child who is unable to comprehend what he or she are being asked to do cannot stand up to the rigors and discipline of the training programme emotionally, then the coach/instructor must rapidly recognize this aspect and take appropriate action. Correction of this type of problem can include redirecting the young person towards other types of activities that are less physically demanding.

Not all children are ready to undertake resistance training tasks from a physical or physiological aspect. For children, Tanner staging by medical personnel could be performed; however, realistically this process is time-consuming, personally invasive and expensive. So, again, it becomes a problem/question the coach/instructor has to consider, making a decision concerning the appropriateness of resistance training and the type of programme that would be most useful. A primary conceptual consideration is that the coach/instructor must be able to appropriately distinguish differences between chronological age and physiological age (Tanner stage) as well as recognize differences in emotional and psychological maturity.

Interestingly, it is quite common to find strength training and weightlifting facilities restricted up to the age of 16–18 years. Consider Naim Süleymanoğlu, arguably the best weightlifter of modern times (Turkish three-time Olympic winner, seven-time world champion and established 46 world records); it is known that he began training at 10 years old and set his first world record at the age of 15 years 9 months. Although Süleymanoğlu was exceptional, had he been in most Western countries it is likely that he would have been waiting to get into a gym until he reached at least the age of 16 years, and certainly not lifting at international level. This observation raises an important consideration of chronological versus physiological age. Not uncommonly, a child can be physically and physiologically more advanced than his or her chronological age; therefore, hard and fast rules of creating training programmes based solely on chronological age should be viewed with considerable caution.76

Both the trainee and the supervisor need to understand safety standards, correct spotting techniques and how and when such techniques should be used. Although uncommon compared with most sports, resistance training can result in injuries, on occasion severe injuries. However, the incidence of injury is relatively low compared with most physical activities and sports.55 Arguably, most injuries occur as a result of poor fatigue management, particularly among advanced athletes. However, the acute injuries experienced in training often result from poor technique or lack of adherence to simple safety procedures, including reasonable supervision.10,11,28,33,60,73,76

Injury potential can be markedly reduced by implementing some ‘common sense’ safety guidelines. These guidelines include:10,11,76,77

  • educating all participants on sound safety procedures;

  • ensuring that appropriate emergency assistance procedures are in place in case assistance is necessary;

  • making sure that the training area is kept neat and clean and that no obstacles are present, particularly on and around the lifting area;

  • making sure that all participants warm up appropriately before each training session;

  • permitting participants to have ready access to fluids during and after training;

  • making sure that lifters understand proper breathing techniques and how these techniques may reduce injury;

  • making sure that appropriate spotting techniques are used, especially for squats and bench-press exercises;

  • teaching athletes performing weightlifting movements (snatch, clean and jerk) how to miss correctly in order to avoid injury;

  • making sure that each session is appropriately supervised by a qualified individual.

The child must fit the training equipment. Although the quality of instruction offered by the coach/instructor is probably the primary factor determining whether or not children and adolescents can achieve resistance training ‘success’, the equipment used can also have substantial impact. The training equipment should be in working order and regularly inspected for potential breakdown. Most machines are made for adults and are not necessarily adaptable for smaller bodies. Although some companies make equipment specifically for children, the use of free weights should be considered the major mode of training for a number of reasons that include evidence that indicates that the use of free weights such as barbells, dumbbells and associated racks and benches produces superior results, especially in terms of transfer of training effect.78,79 Free weights can allow the use of multijoint exercises (such as squats and pulling movements) that are quite similar to multijoint activities of many sports and even daily living; thus, it may be argued that mechanical specificity is greater using these exercises than using machines. Large muscle mass and multijoint exercises are metabolically more taxing and can potentially alter body composition to a greater extent than smaller muscle mass exercises. Free weights can fit accommodate different body sizes, and smaller barbells (length and diameter) are available for women and children. As a result of the equipment fitting the child, the performance of a number of exercises not typically available on machines is possible. The adaptability of free weights allows a large variety of exercises to be performed, which can help reduce training monotony, promote training interest and potentially keep the child/adolescent looking forward to future training sessions.

The child and the supervisor must understand proper lifting techniques for all exercises in the programme. Technique refers to a mechanical idealized pattern of movement that, based on evidence, would provide optimum performance for a specific exercise. Skill level deals with the degree to which an ideal technique can be achieved. Understanding appropriate technique and achieving high skill levels are important for several reasons including:10,80

  • Poor skill results in poor adaptation, limits gains in performance and results in stagnating progress.

  • From a sports perspective, high skill levels can substantially enhance the ‘transferability’ of the exercise to sport performance. Therefore, with low skill levels the potential for enhanced gains in sport performance activities is reduced.

  • Good technique reduces the injury potential and should be taught and learned initially in a child’s or any beginner’s development.

For these reasons, development of high skill levels as rapidly as possible at the initiation of developmental training is paramount. This necessitates a clear and detailed understanding of technique, recognition of skill level achievement and the ability to teach it effectively. Early emphasis on technique and skill level achievement is especially important for large muscle mass and multijoint exercises. Skill level, poor or otherwise, initially developed and used for long periods (i.e. several years) may be difficult, if not impossible, to alter. The establishment of high skill levels from the start of a training programme is crucial to enhance safety, optimize progress and success and provide greater satisfaction. In this context, lack of sufficient strength will limit skill acquisition.10,80,81 Therefore, maximum strength should be enhanced (perhaps proceeding) simultaneously with skill acquisition.

The child should follow an evidence-based resistance training programme. A variety of strength training programmes for use by children and adolescents have been suggested to be efficacious.28,33 The majority of these programmes suggest that higher repetitions (10–15 repetitions/set) should be used. However, and importantly, this type of training for any age should be initiated only after adequate skill levels have been established. In our opinion, and that of others,81 reasonable skill is best established with one-on-one supervision and by performing repetitions one at a time with feedback from the coach after each repetition. If adequate skill level is not achieved then corrections should be made before going on to the next repetition. This one repetition at a time approach is especially important in learning the required technique of complex multijoint movements such as jumping, squatting, snatches or cleans, or their derivative movements.

Only after high skill levels are achieved for each exercise should multiple repetitions per set be allowed. Otherwise, the multiple repetition approach simply promotes poor technique development. After learning proper technique the type of programme used depends on the age and goals of the child, but generally higher repetitions per set would be in order for beginners.

Early training with young children (aged 8–10 years) should use multiple repetitions per set (8–12 repetitions/set), with a training session frequency of 2 to 3 days per week, and with substantial variation of exercises.10,81 Although not always appropriate in a competitive sport context, allowing children and young adolescents to take part in planning the programme (e.g. pick out some exercises) may improve motivation and adherence.

Initially training might use one set per exercise; however, training should rapidly progress toward a periodized training programme and the use of multiple sets.11,33,76,82 The programming for the periodization process includes heavy and light days, ‘unload’ weeks and active rest periods. Using repetition maximum (RM) zones and training to failure are potentially counter- productive programming characteristics and should be avoided.8385 Using periodization concepts and appropriate programming can promote fatigue management, enhance recovery and enhance training adaptation. Strength training should not be considered as outside the normal training paradigm; rather, this aspect of training must be appropriately and fully integrated into the overall training process, otherwise optimum gains and performance improvements may stagnate and the potential for injury and overtraining will increase.72,83,84,86

The coach/supervisor must understand the potential results. Obviously, considering the many studies and reviews of various types of training programmes, not all of these produce the same adaptations.78,87 Basically, the conceptual blueprint (e.g. periodization model) and programming directs the psychological, physical, physiological and performance adaptations (or lack of adaptations). Considering this concept of ‘direction’, perhaps the most important element in the entire training process is the coach/instructor’s knowledge of potential outcome. The coach/instructor is responsible for creating and implementing the training programme. If the coach/instructor does not have sufficient knowledge of the training process and the potential result, then training can become a relatively random process with an infinite number of possible qualitative and quantitative outcomes.

A background in sports and exercise science is necessary to properly construct a training programme. Sport science is the study of sport. It is concerned with the application of scientific methods and principles to enhance sports performance. Sport science generally incorporates the areas of physiology, biomechanics and psychology, but also includes other fields such as motor control and development, and nutrition.86

Sport science is closely associated, but not synonymous, with exercise science. Exercise science can be considered to be the study of biological responses and their adaptations to exercise and training. Currently, exercise science focuses primarily on health, health-related performance and their underlying mechanisms. Exercise science can be applied to sports only indirectly.88,89

Coaching is a combination of science and art. Considering this point, becoming a good coach is similar to becoming a good medical doctor. A good physician will endeavour to obtain a good science background in order to better practise the art of medicine. Similarly, a good coach should make every effort to obtain a good scientific background to better practise the art of coaching.90

A scientific background aids in providing an evidenced basis and sound rationale in selecting appropriate methods and directing adaptations towards more specific goals. A sound scientific background enables the coach to make choices about training and competition that might not otherwise be possible.11 Part of this scientific underpinning should also entail understanding the differences between training children, adolescent and adults.86

Value for youth sports

Substantial evidence indicates that stronger athletes have distinct performance advantages in a wide variety of sports and sport-related parameters.2,91100 However, gaining maximum strength and resultant improved performance depends on many factors within the training process, such as the appropriate manipulation of volume and intensity, exercise selection and appropriate timing of the degree of specificity, the length of training, expectations concerning a potential lag time (time it takes to ‘transfer’ strength gains to sport performance, which can be several months), current and potential future fatigue levels, and the level of athlete.78,101 Considering the relationship between strength and other performance activities, it is reasonable to believe that resistance training among youth would have a large potential impact on their performance abilities.

Considering the positive and substantial alterations in adults as a result of strength training; of particular interest for this discussion is to what degree can resistance training effect similar alterations in physiology and sport performance among children, and early and late adolescents? When addressing this question, initially one must start with a simple observation. It is readily apparent that, compared with their weaker counterparts, in most sports stronger children and adolescents reach high skill levels more rapidly, progress at a faster rate and are able to transfer strength into their sport performance more readily. This observation is especially apparent in strength–power sports such as gymnastics, throwing, rugby or sprinting. This conclusion is not based on casual observation, but rather years of careful, detailed observation and monitoring of athletes, as well as discussions with developmental coaches and sport scientists interested in this area.

Studies examining relationships among these variables also support these observations. For example, Carlock et al.92 found strong correlations among vertical jump performance characteristics, power output, weightlifting movements (snatch, and clean and jerk) and the 1 RM squat among junior weightlifters. Young et al.,102 investigating junior track and field athletes, found that ‘strength qualities’ were strongly related to sprint performance.

An 8-month longitudinal study leading up to the Sydney Olympic games found that the Bosco Test (60-second explosive strength–endurance jump test) could predict 92% of members of the 2000 USA gymnastics Olympic team and later predicted who would actually be on the floor competing and which athletes would be alternatives.103 Moreover, the average Olympic gymnastics team athlete outperformed non-Olympic team aspirants on every physical ability test, most of which required high levels of strength, explosive strength or strength endurance.104

Although careful observation and correlational studies are a first step in the development of understanding ‘cause and effect’, these observations and studies are not definitive. In order to more firmly establish cause and effects, longitudinal studies are necessary. Most longitudinal studies have supported these observations and the correlational studies.

Although not all studies agree, several studies indicate that resistance training, including non-specific programmes, can enhance performance in children and adolescents. For example, motor performance has been shown to be markedly increased among children.30,42,105 These studies included alterations in strength, flexibility, jumping and sprinting abilities. Using high school-aged (14–18 years) American football players, Cahill and Griffith106 found that resistance exercise increased maximum strength and was related to better sport performance and fewer knee injuries. Swimming times (100 m) were not affected by short-term (6 weeks) non-specific isometric strength training107 among children and adolescents, but longer periods of dynamic strength training were shown to result in improvement.108 Improvement of maximum strength of the knee flexors/extensors through a resistance training programme improved time to peak force, as well as landing mechanics, among high-school female athletes. Results such as these indicate that resistance training can potentially enhance jumping performance and reduce injury potential.109 A periodized resistance training programme lasting 12 weeks among high school baseball players resulted in increased linear bat velocity, bat centre of percussion velocity and hand velocity.6

Weightlifting training has been used to examine the effects of a number of performance and physiological variables among children and adolescents.7,13,22,66 For example, among boys aged 11 and 12 years, weightlifting training produced distinct increases in strength and speed–strength parameters, as well as measures of cardiorespiratory fitness.70 Dvorkin66 has discussed in detail the results of a series of studies carried out in the Soviet Union beginning in the 1950s and continuing through the 1980s, examining the effects of weightlifting training on the physical development, physiology and performance of children and adolescents. The data derived from these studies indicate that from 12 to 22 years of age weightlifting training can produce positive alterations in body composition, cardiorespiratory variables (e.g. resting heart rate, blood pressure, physical working capacity) and a variety of motor fitness parameters (e.g. jumping and sprinting), as well as in weightlifting performance.

Considering the observational, correlation and longitudinal data as a whole, there can be little doubt that resistance training, including weightlifting training, results in improved strength and strength-related variables (e.g. RFD, power, strength endurance, etc.) among children and adolescents. These studies also provide evidence for the efficacy of strength gain alone in creating beneficial alterations in skill-related variables among children and adolescents. Furthermore, the data indicate that sport performance can be positively enhanced with well-planned and -executed resistance training.

Psychosocial aspects

There is evidence that appropriate physical training can promote psychological well-being and character development.30,110 Coaches/instructors can consider linking aspects of training to other facets of life, and that these difficult parts of life can be overcome with similar diligence. Therefore, it can be argued that training, including training for sport, can be a positive force in the young person’s life. Sports training has long been recognized as a primary tool for instilling important societal values and ‘life in microcosm’, such that participants are offered opportunities to practise many of our most highly prized character traits.

Training, particularly resistance training, can have a considerable impact on several emotional and psychological aspects of people at all ages.28,33 Among adults, resistance training has been shown to improve measures of self-image, self-esteem, body cathexis and general outlook on life.111113 These data for adults agree with observations in children and adolescents.31,60 As with performance and physiological alterations, it is likely that methods for manipulating programme variables (i.e. volume and intensity factors, exercise selection, etc.), when used appropriately, can have a substantial and profound influence on the psychological alterations that can be derived from the training programme.

As with good health, the best practice is to create an environment for the child (or adolescent) that prevents any negative behaviour arising in the first place. Children may arrive at the gym with pre-existing psychological problems; however, it is possible that negative psychological issues could develop in training and in competition as a result of the use of poor coaching methods. Just as children can be taught poor lifting technique and thereby develop bad habits, so can they develop negative psychological behaviour from poor coaching methods and an emotional/psychologically negative environment. Whether physiological or psychological, both are difficult to correct. It is important to develop correct lifting technique and initiate the development of a sound physiological basis and positive psychological habits from the first day of training. Additionally, psychological strategies employed in competition must be put into practice in training on a daily basis.

Record-keeping is necessary for monitoring the training process and should be started at the beginning of any training programme. The record keeping creates a history for the child or adolescent, so that progress can be charted. These records can provide strong evidence of positive progress and reinforce positive emotional and psychological factors for the trainee.

Record-keeping is an excellent tool for promoting self-confidence, particularly when promoting individual achievement. Personal records on a variety of lifts should be recorded both single repetition maximums and for multiple repetitions.

Weightlifting for children and adolescents

Weightlifting is a competitive sport that consists of the snatch and clean and jerk. Training for weightlifting primarily incorporates using a variety of large muscle mass exercises, such as squats and variations, snatch, and clean and jerk and variations.

Weightlifting, based on entries by country in the Olympics, is one of the most popular sports around the world. Considerable study has been devoted to the sport of weightlifting and its effects on competition performance, transfer to other sports’ performance and injury potential.72,114,115 Although the potential benefits of strength training are now recognized by most medical/scientific groups concerned with children and adolescents, the controversial aspects tend to reappear when dealing with training for sport, including weightlifting.9,10 Over the past 20 years weightlifting has come under increased scrutiny and has been more controversial than any other aspect of resistance training for young people. For example, the use of ballistic and semi-ballistic movements, such as weightlifting movements and derivations and plyometric exercises, and particularly the sport of weightlifting, have been criticized in opinion articles as producing excessive injury rates.116 A recent review on children and young adults participating in resistance training states that ‘powerlifting and heavy weight training should be avoided, as lifting maximal weights through various ranges of motion as fast as possible can lead to serious limb injuries’.117 This review might possibly be suggesting that the sport of weightlifting should also be avoided by children and young people, as lifting maximal weights fast describes weightlifting and not powerlifting. Although injuries can occur during weightlifting and related activities, the incidence and rate of injury appear, to be relatively low and severe injury is uncommon.55,118

With appropriate supervision and coaching, most injuries among children and adolescents associated with strength training activities appear to be preventable. These injuries are largely avoidable accidents.119 However, controversy concerning weightlifting and youth still exists, even though information is available indicating that, under proper supervision, these activities are no more (and usually less) injurious than other sports.10,28,55 Assuredly, arguments can be made that weightlifting training and related strength-training activities can substantially enhance health-related characteristics and, in fact, reduce the injury potential of some activities and sports.55,72

In the Soviet Union weightlifting was a very popular and competitive sport. Indeed, considerable study was devoted to the effects of weightlifting training, particularly among children and adolescents. The previously mentioned studies reported by Dvorkin64 are particularly convincing as, in many cases, large groups were tracked continuously from the age of 13 to 19 years and compared with control groups of non-exercising peers or similar age groups involved in track and field sports. These observations and studies indicated that weightlifting training produced positive improvements in body composition, cardiorespiratory variables and general well-being. Furthermore, there was no indication that weightlifting training ‘stunted’ growth. Additionally, it was noted that injury rates associated with weightlifting are typically lower than those linked to other forms of resistance training.55

Interestingly, over a 1-year period no days of training were lost from injuries as a result of weightlifting training and competition performed by 70 male and female children ranging in age from 7 to 16 years {mean age of 15 girls 12.3 [standard deviation (SD) ± 2.6] years; mean age of 55 boys 11.6 (SD ± 2.0) years}.9 Maximum and near-maximum lifts in competition were allowed provided appropriate skill level (reasonable technique) was maintained. As measured by training records and weightlifting performance, both boys and girls showed increased strength and explosive strength.9

Similar results were found in a more detailed follow-up study of three girls [mean age 13.7 (SD ± 1.2) years] and eight boys [mean age 12.5 (SD ± 1.6) years] across 1 year’s competition (534 competition lifts), and both the boys and girls showed marked increases in weightlifting performance. Furthermore, no injuries requiring medical attention or loss of training time occurred.7

The conclusion from these two observations was that, if training and competition are age group appropriate and are properly supervised, weightlifting training and competition can be substantially safer and more efficacious than has been generally believed.10 The authors emphasized that these results must be viewed in the context of a scientific and reasonable approach to training and competition.7,9 Only under these conditions, the authors suggest, does resistive training or weightlifting is appropriate for any age including children and adolescents – a factor that should be true for all sports. Indeed, understanding developmental factors, including the necessity of appropriate supervision and coaching, is absolutely essential when training children and adolescents.120

According to Balyi and Hamilton,121 8–12 years of training is necessary for a gifted athlete to reach elite levels, and there may be ‘windows of opportunity’ or critical ages at which specific types of training can yield the greatest benefits.10 Although this long-term development model has been accepted by many coaches, the scientific evidence for ‘windows of opportunity’ or ‘critical windows of development’ has been questioned.122 Despite ambiguity and controversy surrounding this model, there does appear to be a physiological basis for improvements in motor performance throughout childhood and adolescence.10,63,123,124

Consequently, the possibility for the existence of these windows presents a potential for unique training opportunities to maximize strength, power and speed gains for young athletes. To some extent this type progression can be noted in American football and basketball with 3 years’ participation in middle school, 4 years in high school, and generally 4–5 years in college before potentially participating in professional sports. However, it may be argued that specialization often occurs too early and, too often, well-meaning but overzealous coaches and parents often try to hurry the developmental process in many sports, including weightlifting.10 Evidence indicates that attaining physical literacy involves the development of proficiency in fundamental movement skills (e.g. walking, running and jumping) and fundamental athletic skills (e.g. catching, hopping and galloping), which, when summated and refined, can result in more skilful movements in a variety of athletic and sporting activities.125

Prior research indicates that peak brain maturation occurs approximately between the ages of 6 and 8 years, and again at 10 and 12 years,126 and that there can be a simultaneous accelerated development of the neuromuscular system.127 Certainly, by 12 years of age most of the neural pathways for fundamental movement skills will be defined. The degree and rapidity of this definitive process depends largely on genetics, but is also influence by metabolic and environmental factors.10 This evidence suggests that the prepubertal and peripubertal years are likely a critical time frame for introduction and development of superior skill levels, including those associated with weightlifting.81 In the evaluation of reasonable starting ages for children and the development of appropriate training plans, it is logical that the opinions of coaches dealing directly with children be carefully considered.

In the authors’ opinion, the appropriate age for the initiation of weightlifting training can be as young as 10–11 years, provided that the biological age of the child and the emotional maturity of the child are reasonable. We further suggest that, in the early stages of training, the ratio of technique work to more general strength and conditioning should be approximately 50% light technique, 25% basic strength training and 25% basic conditioning training.

Our opinion is largely supported by the observations of other scientists and coaches; for example, Aján and Baroga62 indicate that the ‘initial stage of training’ for weightlifting should take place between the ages of 11 and 16 years. Starting at the ages of around 11 or 12 years, they strongly indicate that the aim of training should focus on general physical preparation (development of fitness characteristics such as strength, specific flexibility, etc.) and that specialized training should not constitute > 40% of the total training process during the first year. Accordingly, we recommend that during the first year, as a minimum, a variety of dynamic exercises, including exercises that can assist in the development of movement characteristics necessary for weightlifting development (and sport in general), are vital. Additionally, various activities such as basic gymnastics movements, and track and field activities, along with court games such as basketball and volleyball, can be used as part of the training at this age.

Free-weight exercises aimed at general strengthening should be used. Aján and Baroga62 also suggest that the aims and objectives in the second year of training (aged 12–13 years) should largely centre on general physical development (50%) and stress ‘correct habits of execution’ when learning the technique of the competition exercises. Specialized training should be added gradually in subsequent years and, to optimize long-term results, each phase of training should be built on the previous phase. According to Ajan and Baraoga,62 specialized training should increase relatively gradually. They suggest that more specialized weightlifting training should increase to 55–60% of the total weightlifting process in the third year and to as much as 70% in the fourth year.62

Interestingly, in Bulgaria, from 1983 to 1993, the starting age for weightlifting training decreased by an average of 2 years, leading to 10- to 11-year-olds being ‘selected’ for inclusion in weightlifting programmes. In this small country that had been highly successful in weightlifting, the recommended age to begin training was 10 years, and similar programmes were set up in other Eastern European countries.63 Furthermore, it should be noted that many (and probably most) of the athletes participating in many Eastern European weightlifting programmes were initially selected based primarily on a comprehensive talent identification search.63 Children at these recommended ages should begin with general physical development that is compatible with sport-specific fitness, and this emphasis should continue for at least 2–3 years.62 Compatibility with sport-specific fitness is important as some evidence indicates that non-compatible exercise (e.g. endurance activities plus strength–power activities) may compromise the desired goals. For example, weightlifting developmental fitness for children would include considerable training dealing with basic body strengthening (e.g. weight training, gymnastics, tumbling), strength–endurance factors and enhancing cardiorespiratory capacity through interval and metabolically stimulating resistance exercise, and exercise aimed at increasing mobility and range of motion.

It should be noted that evidence among adults and adolescents indicates that emphasis on cardiovascular endurance that includes typical aerobic exercise (e.g. long-distance running, swimming, cycling, etc.) should be limited or avoided as this may compromise the ability to gain strength and particularly RFD (explosiveness) and speed of movement.128

A typical timeline for a child’s development and a typical training programme that could be used with a weightlifting beginner should be encompassed in basic strength training that includes body weight movements in the youngest age group (e.g. gymnastics), progressing, fairly rapidly, to the use of free weights (e.g. squats, pulls) with minimal loads and emphasizing the attainment of superior technical skill levels. Indeed, at the initiation of technique training, age- and size-appropriate bars should be used, progressing to standard bars and additional loading as skill level and physical development become appropriate. The aim of this type of training should be to develop technical proficiency in weightlifting movements and exercises that are associated with development, such as weightlifting derivatives, squats and presses, and will overlap with strength training. Basic conditioning should include components including flexibility, sprints, bounding, hopping, games such as soccer and basketball, and gymnastic exercises.

Differences in training male and female children and adolescents

Currently, the popularity of all forms of resistance training among women and girls is at an all-time high. Although resistance training, particularly for sport, was once considered to be ‘for men only’, this is clearly no longer the case. Women and girls have broken with tradition and cultural mores, and now wholeheartedly engage in various strength training activities, including CrossFit, bodybuilding and the strength/power sports of powerlifting and weightlifting.

Among adolescents, gains in maximum strength and related characteristics can be greater than in children, and the absolute gains do reflect some substantial sex differences. Qualitative adaptations to strength training in adolescents and the young are largely similar to those seen in younger boys and in men.7,9,11 However, genetic, structural and hormonal differences appear to create enough variance to warrant alterations in the training of adolescent females in order to concentrate on specific mechano-physiological differences. A striking difference between the sexes deals with anabolic and catabolic hormones.

Androgens, especially testosterone, influence a variety of sex characteristic-linked physiological differences, such as LBM maximum strength, peak RFD and power output.129,130 Many of these differences are accentuated on reaching adolescence.131

With considerable certainty, higher testosterone concentrations not only appear to be related to strength and explosive strength performance differences between men and women, but also may explain many intra-sex differences.132 Furthermore, the rate of training-induced adaptation can also be influenced by differences in resting testosterone concentrations. Thus, women or girls with higher concentrations may adapt and show progression at a faster rate.130 Some ex differences, such as physical and structural differences, that become more apparent in adolescents133 can result in training outcome differences or necessitate programming differences.

For example, women have relatively less upper body LBM and muscle than men. This difference appears to be reflected in lower absolute and relative strength measures in women than in men.134 As a result of these upper body muscle size and strength differences, additional training of the upper body during specific phases of training, or for specific activities in which the upper body is more active (e.g. throwing and aspects of weightlifting), may be necessary. This difference is of particular importance as lower body activity performance outcomes can be linked to the upper body, for example squats in which the load is placed on the shoulders (i.e. upper body). A relatively weak upper body could limit squatting ability as the necessary support for holding the bar along the shoulder girdle is reduced. It is possible that early recognition and appropriate intervention could largely prevent this potential problem.

Strength is an ability to produce force and ranges from 0 to 100%.5,79,99 It should be noted that the display of maximum strength is, to an extent, task specific and can be defined as the greatest force that can be generated under a given set of circumstances. Strength should be thought of as a vehicle that is accompanied by several important strength-related characteristics such as explosiveness (RFD), power (P) = force (F) × velocity (V), and the ability to accelerate and achieve a velocity of movement [F = (mass × acceleration (MA)]. Explosive strength or RFD is one of the most important attributes that athletes should develop and is especially important for weightlifters as it is a key characteristic in defining impulse [F × time (T)] and power output.

Many sports depend on maximum strength, explosiveness and high-power outputs. For success in producing reasonable performance gains in these ‘explosive strength sports’, it would be desirable to enhance maximum RFD development and peak power outputs. Several sex differences must be considered. Electromechanical delay, contraction times, RFD and power output are typically lower in women than in men.135,136 These differences may partly be accounted for by androgen differences132 and, as the child reaches puberty, by menstrual cycle factors. These sex-linked characteristics can be related to differences in performance and injury rate between men and women. For example, in terms of performance, maximum strength is a major factor in weightlifting. Explosiveness and power output are also key elements for weightlifting success and accompany gains in maximum strength.5,97 Women’s peak power output during weightlifting movements is approximately 65% that of men. Initially, young women who become involved in explosive activities such as weightlifting, should concentrate their training on gaining maximum strength, as increases in maximum strength have been shown to result in, gains in explosiveness and power that are equal or even higher than gains in primarily training power.5 It should be noted, however, that at no time during training should power be neglected; rather, it should be more or less emphasized depending on the current goals of training. As maximum strength levels are increased, emphasis should switch towards power and explosiveness training.5

Even though men and women weightlifters often train in a similar manner, coaches should recognize sex-linked characteristics that can result in performance problems, including differences in upper body strength, electromechanical delay and skeletal muscle contraction time and menstrual cycle characteristics. As a result, training can be manipulated and altered, often subtly, at specific points developmentally or during specific phases of a periodized programme. These alterations can include additional upper body work during preparation, specific strength, reactive strength and explosive exercises to address differences in electromechanical delay, force absorption, active joint stabilization and biomechanics that have been associated with a relatively greater potential for injury, particularly for the anterior cruciate ligament.

Strength training, as well as specific neuromotor training (e.g. exercise to alter landing patterns after jumping), has been shown to reduce these sex-related differences in injury potential among young women.137,138 Therefore, it is likely that specific training programmes may promote enhanced performance gains, perhaps decreasing the gap between men and women as well as reducing injury potential. These arguments concerning strength training can be made for a variety of sports requiring high levels of maximum strength, explosive strength and power. It must be remembered that optimum adaptation to training also depends on a number of psycho-physiological factors, such as chronological versus physiological age, physical and mental maturity and environmental/cultural conditions such as prior or current involvement with sport, and prior participation in activities that develop physical literacy, co-ordination, agility, balance and flexibility.

In general, training programmes for females should be basically the same as those for males at all stages of development. However, in some circumstances especially when training for sport, specific training differences can be incorporated; these can include a greater emphasis on upper body strength, particularly during early season and preparation phase, on explosiveness and on neurological factors associated with jumping and landing. These differences in training should be implemented to address sex-linked traits that become more obvious developmentally (e.g. child to adolescent). Arguably, the earlier they are addressed, potentially the less of a problem they become as the child develops into an adult.

Recommendations

As with any physical activity or sport, resistance training should be carried out with reasonable injury prevention and safety measures in place. In normal, well-supervised training environments the potential for injury is remarkably low. It is clear that the potential for injury is an issue that requires ongoing scientific study. The need to confirm anecdotal reports and conjecture regarding injury is essential. Training and competition should be carried out by well-qualified coaches and supervisors who have an understanding of sport science and the growth and maturational intricacies specifically related to paediatrics. Furthermore, the coach/instructor should have good coaching skills for this age group, with the ability and motivation to apply this knowledge.

Finally, in support of resistance training for children and adolescents involved in sport, motivation for training would be difficult to sustain without some form of competition in which the role of the resistance training is clearly defined. To some extent, the lack of data dealing with children and competition is the issue; the alarmist negative response by well-meaning physicians, educators and coaches has done an immeasurable disservice to resistance training and the use of resistance training in sport. Indeed, the sport of weightlifting (along with powerlifting) is often condemned by the uninformed as being particularly injurious. However, objective data strongly indicate that resistance training, including the integration of resistance training into sports training and including the sport of weightlifting is actually considerably safer than is generally believed. This is especially true if training and competition are appropriate for the age group and properly supervised.7,9 Weightlifting competitions could and probably should include a focus on technique at early ages (11–12 years), in which the judges rate the skill level of the child, much like gymnastics.139

Based on substantial evidence including the observation of knowledgeable coaches and sport scientists, numerous cross-sectional and longitudinal studies and review of literature, the following should be expected for youth resistance training:711,81

  • Resistance training can increase the maximum strength of children, early and late adolescents. Increases in strength and related characteristics (e.g. RFD, power) during childhood are primarily related to adaptations of the nervous system, with hormonal and hypertrophy adaptations becoming increasing important with growth and maturation. Training can also produce positive psychosocial alterations such as improved self-efficacy, body cathexis and feelings of well-being.

  • Resistance exercise and particularly weight training exercises that have a large technical skill-based component would appear to facilitate enhanced development across a wide spectrum of performances. Owing to the complex motor control/force characteristics required of complex movements,78,135 large muscle mass, multijoint exercises probably facilitate both muscle development and superior neural activation patterns.

  • Although injuries can occur, resistance training, including the sports of weightlifting (and powerlifting), does not result in disproportionate or excessive injury rates, nor are catastrophic injuries common, particularly if the activities are well supervised by knowledgeable trainers and coaches.

  • It should be noted that several questionable practices that can accompany sports training may hinder adaptation to resistance training protocols and may reduce gains in strength and related performance variables. These can include a poorly planned training process, excessive volumes or intensities of training, increasing the intensity and particularly the volume of training too rapidly, and training to failure. Of special note is that unsafe weight loss techniques, particularly through means of intentional dehydration, should not be permitted. This would include but is not limited to use of saunas and body wraps and reducing the intake of fluids.

  • Educators, coaches and supervisors of youth training should be required to demonstrate, through testing, certification, licensure and regular updates, knowledge of safety and proficiency in the sport sciences including the disciplines of physiology, biomechanics, psychology, human development and motor learning, particularly as they relate to resistance training.

  • Coaches, instructors and supervisors who fail in following these recommendations and guidelines should be censured, suspended or banned. The author has confidence that international and national sports governing bodies will institute long-term programmes that focus not only on the elite athlete, but also on the long-term development of potential advanced and elite athletes. A strong and long overdue first step would be the recognition of the considerable importance and significance of appropriate strength and conditioning in the overall developmental process.

There is a need for national and international sport governance bodies to develop an evidence-based framework for a long-term athlete development process that addresses the need for strength and conditioning programmes for youth that can be executed through an integrated training pathway. This type of process should reflect best practice by providing a comprehensive education for athletes, coaches, supervisors and parents in developing and enhancing the physical capabilities of young people. This process should also aim to develop a high level of movement literacy in younger ages, develop sports-specific skill levels, including the development of gymnastic and weight-training exercise techniques, between the ages of 8 and 11 years, and train and deploy high-quality, well-educated strength coaches and weightlifting coaches to further develop technique skills and strength in children across a range of sports after 11 years of age.

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