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ARTICLE OF REVISION Initiation of force training at early ages: review Introduction to strength training at early age: A review Introdução ao treinamento de força em uma idade precoce: revisão G. Peñaa, J.R. Herediaa, C. Lloretb, M. Martínb and hop over to these guys M.E. Da Silva-Grigolettoa,c,d to the International Institute of Physical Exercise and Health Sciences (IICEFS), Spain b Instituto Profesional de Exercise Físico y Cancer (IPEFC), Spain c Scientific Sport, Spain d Universidade Federal de Sergipe, Centro de CiênciasCB and da Saúde, Aracaju, SE, Brazil Correspondence Management RESUMEN The training of strength in prepuber and pubic ages is widely recommended. In this context, this article aims to develop a review of force training at early ages. For this purpose, published works in English were reviewed from 1995 to 2014 in indexed journals, considering those chronologically more recent in the first place. Among the main evidences it can be emphasized that the derivative benefits significantly exceed the risks that this type of training might entail, provided that it is carefully supervised by qualified technicians and the design of the program set adapted to individual characteristics, needs and objectives. In addition, the training program should contemplate the proper dose of neuromuscular exercise of each of its components and the way to progress with them sensitively over time. Palabras clave: Training against resistance. Pre-puberes. Teenagers. Young. Children. ABSTRACT Strength training in prepubertal and pubertal age is widely recommended by scientific organizations responsible for overseeing the healthy training of these populations. In this context, onepatient.wiki this paper aims to develop a critical review of the strength training at early age. To this end, papers published in English were reviewed from 1995 to 2014 in ISI-indexed journals, considering those chronologically most recent first. Among the main evidence we can point out that the benefits far outweigh the risks that could lead to this type of training, provided it is carefully supervised by qualified technician and the design of the entire program adapted to features of the subjects, individual needs and goals. Also, the training program shall provide for the particular dose of neuromuscular exercise of each of its components and how steroids work to progress substantially the same over time. Keywords: Resistance training. Pre-pubertal. Teenagers. Youth. Children. RESUMO O treinamento de força em idade pré-adolescente e teen é amplamente recommended by organções ciencias responsáveis by supervisionar a formação saudável dessas populações. Neste context, or present trabalho tem as objective desenvolver uma avaliação do treinamento de força em uma idade precoce. For or ephey, articles published em inglês foram revisions between em newspapers indexed no ISI, considering that is chronologically mais recentes primeiro. Between the beginnings of the evidências it may be emphasized that you beneficios superam em muito os riscos que poderiam levar a este tipo de treinamento, desde que seja carefully superviseado por pessoal qualificado e todo o design do programa adapted às características, necessidades y objetivo individuais. Or program of treinamento will see to include two adequates of neuromuscular exercio of each um two seus components and as progredir substantially or mesmo ao longo do tempo. Palavras-chave: Treinamento de força. Pré-puberes. Teenagers. Youth. Crianças. Introduction During the 1970s and 1980s there was a clear reluctance and caution in recommending the training of force for the various age groups of children and adolescents. Part of this could be due to the fact that some preliminary studies did not find any improvements in the force of prepuber children who participated in force training programmes1,2, which led to the generalized view that this type of training was ineffective for this population, including by the American Academy of Pediatrics in its first published recommendations in this regard,3.4. At present, and JBH News from the first position published by the National Strength and Conditioning Association in 1985 regarding the training of force in the pre-pubescence5, and its subsequent updates,6.7, it can be said that there is a great international consensus between health-related and training-related associations, in supporting the supervised participation of young people in force training for being recognized their safety and effectiveness for improving health and performance. In the same vein, the last published international position8 reinforces and strengthens the recommendation and promotion of neuromuscular conditioning programs during childhood and adolescence, provided that they are properly supervised and designed by qualified adults to train this type of population. Therefore, the aim of this review work is to summarize and update scientific knowledge on different topics and guidelines related to the prescription of force training in young prepuber and adolescent populations. Method The search for articles for this review was carried out in the databases PubMed, Scopus, SportDiscus, ScienceDirect and Google Academic, using the terms children, adolescents, youth, youth athletes, pediatric, as well as their combination with the terms strength training, resistance training, weight training, motor performance skill. Work published in English from January 1995 to January 2014 was fundamentally reviewed in journals indexed in the Journal Citation Reports of the ISI Web of Knowledge (Thomson Reuters Corporation), selecting those of greater relevance according to the criteria of 2 independent researchers, on a total of 363 references. The inclusion criteria used by researchers for the selection of the most relevant articles were, English as a publication language, the impact level of the indexed journal and the year of its publication, considering those chronologically more recent in the first place. The exclusion criteria were, not being published in English indexed journals, and/or being articles translated into Spanish from an original article. According to the keywords and their combinations, as well as the criteria for the inclusion and exclusion of the articles, a total of 67 scientific articles were obtained (Fig. 1). Figure 1. Studies obtained in databases evaluated for inclusion. Demitification of force training at early ages Insecure practice due to high incidence or risk of acute muscle-skeletal lesions and overload. There is no scientific evidence based on intervention, descriptive and observational studies that have been statistically able to show higher rates of injury in children ' s and pubic populations that practice force training than those that practice other forms of physical-sport exercise. In fact, data show that early-age strength training is highly safe if it is properly supervised by qualified adults who properly instruct. It is estimated that the risk of harm in these cases is as low as 0.0012-0.0035 injuries for every 100 hours of training.89, which constitutes a risk similar to or less than that assumed for other sports and recreational activities usually practiced at the same ages.10 All experts agree that most of the injuries in young people, which may occur during the training of force, navigate to this web-site are due to accidents caused by the inappropriate use of the equipment (77.2% in young people 8-13 years)11, to an excessive training load, to a defective execution technique and/or to the absence of qualified supervision. This can lead to the deduction that by identifying and caring for all aspects related to the safety of the environment and training equipment, progression and individualization of the training dose, the correct technical teaching of each exercise and strict supervision, the potential risk of harm during practice can be prevented and minimized at these ages. Harmful effects on bone development and full body growth. There are no documented evidence showing or linking adverse effects that may interfere with linear growth and the final stature reached in prepubers and pubes with the training of the 12-15 belly. There is also no scientific evidence of potential injuries to growth cartilage (growth plates) or premature closure of epiphysis in prospective studies with young people in programmes under qualified supervision and appropriate force training prescription7-9,16,17. On the contrary, it is possible that there is potentially greater risk to the growth plates of young people who perform competitive sports activities involving jumps and landings, where the reaction forces against the ground can become 5-7 times of the body weight.9 On the contrary, the exposure of developing growth plates to sufficient mechanical stress through appropriate strength training can be a beneficial stimulus for bone formation and growth.7 Inoperative conception of force training at early ages. This conception led to the thought that the training of force at early ages, especially before puberty, was unproductive and ineffective as no benefit was obtained. It was thought that the development of force was closely conditioned by sexual maturing, and that therefore at prepuber ages the child did not have enough potential to improve the different strength and muscle development benefits beyond the development and maturity of his or her age. The argument was that this could be limited in part by the insufficient availability of circulating androgenic sexual hormones in prepuber ages1,3. However, it is highly likely that some of the preliminary studies that failed, in demonstrating improvements in this regard, would not be of sufficient duration or training intensity. However, collecting the results studies, revisions, and metaanalysis of the last 25 years is easy to generally see the opposite effect7,8,13,17-20. For example, in a study by Faigenbaum et al.21 where 1-2 times a week were trained, for 8 weeks, to boys and girls between 7-12 years (1 x machine repetitions), it showed significant force improvements in the exercise of the press of banking and the press of legs compared to the control group of the same age. Other meta-analysis have also been able to check, comparing it to control groups of the same age not subjected to force exercise interventions, greater improvements with the training that would report to it the own development and natural maturation at any age9,19,22. Strength improvements in relative expected terms can be as evident as 30-40% or more, after 8 weeks of training in young dissenters7,8, which demonstrates a similar effectiveness for both sexes with appropriate training. It also seems that such gains of strength and power, induced by training, are temporary and tend to return to the values of those of dissenting control groups, when training is interrupted15,16. It has traditionally been considered that, during the period of time, during which there is a greater concentration and availability of sexual hormones, a better training or response favorable to the training stimulus could be expected. However, in the meta-analysis of Behringer et al.19 on the effects of force training on different age groups and mature levels, such internability, represented by the size of the effect, on the gain of strength, seems to increase linearly throughout all years of childhood and adolescence, without seeing a particularly greater increase during the specific years of puberty, so according to the opinion of these authors, the increase of hormonal importance is improbability. Given these evidences, it can be said that preteen and adolescent children have good training, showing relative improvements similar to or greater than in adults, when training is properly designed and adapted to their abilities. Potential benefits of force training at early ages Prevention/reduction of the incidence of injuries induced by physical-sport practice. The implementation of properly prescribed and supervised force trainings in global physical fitness programs during the pre-season and the sports season has shown that it can reduce the incidence of sports injuries in children and adolescents.823. On the contrary, young athletes who do not have adequate levels of strength and physical conditioning will have more risk of sports injuries.15 Lesions as common as breakages of the anterior cross ligament of the knee in young athletes (v.g.: football, rugby), can be prevented in frequency and severity by incorporating a proper muscle conditioning program during the pre-season24-26. In short, force training can help physically prepare young athletes, to deal with the high muscle-skeletal demands of sports training and competition with greater guarantees. However, physical inactivity is itself a risk factor that predisposes injury during physical practice, to the extent that overweight or obesity adolescents have more than twice the chances of injury than their counterparts with normopeso27. Those force training programs, which focus on injury risk factors associated with sports injuries (v. g.: muscle imbalances, low level of initial neuromuscular fitness), have the potential to reduce the incidence of overload injuries to 50% in children and adolescents.28 In this way, the inclusion of specific neuromuscular conditioning programs, in young athletes of years, has shown, in addition to reducing the rate of injuries, to require less time for recovery after injury than in teammates who did not do it23. Enhancements of muscle strength and performance in motor skills. Scientific literature on this aspect is also firm, properly prescribed and supervised strength training has the ability to generate performance improvements in motor skills (jumping, forum.veriagi.com running, throwing) in children's and youth ages, which can have a transfer to improve other sports-type capacities20. We have a growing body of scientific knowledge that attests that the training of force at these ages can lead to increases in motor performance through increases in strength, speed, power and other related features29. The most effective training programs seem to be those with a minimum duration of 8 weeks and multiple series7,8, which, if possible, should continue in the long term to strengthen and maintain the adaptations achieved. On this point, the meta-analysis of Behringer et al.20 is particularly noteworthy, which analyzes the effect of force training on children and adolescents on the motor performance of certain motor skills (traditional and/or pliometric strength trainings). This meta-analysis shows that properly structured force training is effective in improving the performance of the race, jumping and launches. And since the driving performance of such abilities is an essential component in different sports, it is reasonable to assume that there is a specific positive transfer to the performance of many terrestrial sports patterns. The greatest improvements in this regard seem to be made in the younger and desensitized subjects, probably due to the greater neural plasticity and motor learning of children, while there is a positive correlation between motor performance gains and the average intensity used according to the percentage of the best first time steroid cycle maximum repetition (%1RM) with traditional force training programs20. During childhood and prepubescence physiological mechanisms responsible and attributable to these strength improvements are mainly neuronal,30,31 while as the puberty advances the explanatory mechanisms associated with such increases point to being both neural and structural (increments of the lean tissue and muscular cross section)15,29, especially in males. This seems to be so because young men experience a greater increase in circulating androgenic hormones (v. g.: testosterone, growth hormone) which can lead to greater increases in the muscle component. This also explains, in part, that from puberty the differences of strength in absolute values between sexes, in favor please click the next web page of males, begin to be more evident.32,33 However, there is a certain debate that questions the "impossibility" that in prepuberal early stages there can be increases in muscle mass with appropriate training, even though there is no theoretically favorable hormonal environment for it, since some studies cited in revisions and metaanalysis have confirmed significant increases in muscle mass after strength training even in prepuber children.16,19. Perhaps, one of the reasons that can explain it, whether those studies that have used more sensitive techniques to evaluate the increases in muscle tissue (ultrasonides and nuclear magnetic resonance) have suggested that muscle hypertrophy can happen in children after strength training.16 In any case, the contribution of morphological adaptations that can explain the obvious gains of strength that occur in children and preteens after force training is relatively low and often difficult to measure. Therefore, it can be inferred that in children the strength gains induced by training are fundamentally explained by the neurological adaptations that happen (major and more efficient agonist, synergist and stabilizer muscle activation). Among the different neuromuscular adaptations, motor learning can have a higher relative contribution in those more complex exercises from a motor point of view (multi-articular exercises)16. Improvement of bone health. The key evolutionary stages that provide an opportunity to increase bone mineral density and content, and thus achieve a good reserve capital for the future, are precisely childhood, preteen and adolescence.34 During these sensitive periods of bone formation you can acquire 50% of the bone mass peak16. Regular practice in physical-sport activities with body weight support in general, and with a high content of force actions in particular, are powerful osteogenic stimuli that can help, together with other nutritional measures, achieve this goal in these age-old phases35. On this, some studies have found that the density and bone mineral content of teens halterophils is greater than that of controls of the same age that did not perform force training36,37. Although it is true that the peak of bone mass reached at those ages depends on numerous factors (genetics, sex, nutrition, etc.), regular participation in sports and fitness programs that include multi-articular exercises against moderate-to-high-intensity resistances, and pmetric exercises with leaps, can help maximize bone mineral capital during childhood and adolescence.7.8 On the contrary, the failure to perform exercises with sufficient mechanical stress for the muscle-skeletal structures, in those periods so critical for the complete bone development, may predispose the subjects to suffer negative consequences for their long-term bone health.8 Improvements in body composition and insulin sensitivity. Current children and anabolic steroids book adolescents are not as active as they should, and the rate of reduction of their usual physical activity begins in early preteen15. In the face of an increasingly sedentary childhood and youth society, with increasing obesity rates, any exercise intervention that shows improvement or prevention of the development of obesity and associated pathologies should be incorporated. That is why there is currently a growing body of knowledge that shows significant improvements in obese children and adolescents, or at risk of being, about the improvement of their body composition38-43 (decrease in body fat; increase in muscle mass) and/or insulin sensitivity44-47 after progressive participation in force training programs. While young people with obesity or overweight have always been encouraged to participate in aerobic-type activities, excess body weight hinders performance in physical weight support activities, such as running, and increases the risk of muscle-skeletal lesions by overuse48. Therefore, some expert opinions consider that those efforts and campaigns to promote physical activity among the most obese and less impetuously competent children and youth should not begin by prolonged aerobic-type training or participations in sport competitions, but by training focused on force exercises, characterized by intermittent dynamics, by their improvement in motor performance and the benefits of injury reduction.15 In addition, this type of programs are pleasant for this population cohort as they are not so demanding aerobically and provide an opportunity to improve their physical performance and gain self-confidence for it48. In another order of issues, and even in the absence of further well-designed studies, there are some incipient evidence that sustains benefits other than the previous ones and which can undoubtedly serve to open new lines of research in the future, such as improving the heart function in obese children49, improving the lipidic profile of prepubers and teenagers50,51, and the positive effects derived on psychological well-being, mood-52-54 and teen. Together, all these arguments support the need to promote the practice of force training among children and adolescents by the effectiveness shown for improving their health and motor performance. Moment for the start of force training In the past the training of the force was usually introduced at the end of the somatic maturity of the subject (age to which the peak speed of growth in height happens), that is, when it reached the age of 1855. However, it is currently not possible to establish or recommend a chronological age as optimal or minimal, as we can find differences in status or biological maturity between children and young people of the same sex and Full Post chronological age up to 4-5 years.56 This great inter-individual variety in the biological age of children and adolescents of the same chronological age, with important implications, justifies the need to group children and adolescents based on their biological maturity and driving competence to be trained. In fact, it must be a principle of most long-term training programs to ensure that young people are trained according to their biological status, in contrast to classifying them by age groups.8 With regard to the biological maturity of the adolescent, the specialized literature considers basically 4 indicators for its assessment (dental, sexual, somatic and skeletal or bone)56. Traditionally, the assessment based on sexual maturation, by visual observation of the secondary sexual characteristics of adolescents, also known as the Tanner57 scale, has been classically referred to in literature4. This technique allows to classify the adolescent on a scale that varies from stage 1-5. In the past, the American Academy of Pediatrics4 and the American Orthopaedic Society for Sports Medicine14 recommended avoiding the sports practice of halterophilia, power-lifting and body building without steroids-building until the young people had reached the mature stadium of Tanner 5 (full maturity), arguing that these activities entailed increased risk of muscle-skeletal injury and were potentially dangerous for the younger. The latter has also been demented in some publications, provided that these sports are carried out under qualified supervision and instruction and progression is based on the technical quality of each uprising, showing in fact some indices of minor injuries than other sports in general.29 In the year and the same American Academy of Pediatrics pointed out in their statements that pre-teens and adolescents should only avoid power-lifting, body-building and uplifts with maximum weights until they attain sufficient physical and skeletal maturity, which showed a less rigid position on it. In addition to considering the chronological and biological age, those responsible for designing and executing force training programs for young people should take into account the age or training experience8, as in the face of the same biological status, those athletes with more accumulated training experience will be able to assimilate the same training stimuli and progress more quickly. Therefore, it is not currently considered a minimum chronological age required to begin with the participation of children and adolescents in properly supervised force training programmes7,16,23. However, at any age, children and young people should show sufficient emotional and psychological maturity to attend to the instructions of adults in charge of their supervision and be able how to cycle steroids undergo the stress of a training program, in addition to having competent levels of balance and posture control7,8,19,23. In general, at the time a child is trained to start in sports activities (usually at 7 or 8 years old) he will also be able to start with force training3,23. Although a previous medical examination to be able to perform a force training program is recommended in seemingly healthy children, it should be mandatory for those with symptoms or signs of disease and for those with recognized diseases7. However, the importance of the medical pre-participation of sports should not be underestimated by its relevance in order to provide security for the early training of force in any age and condition group. In the same way, in order to begin a training of strength at an early age, it will be essential, as has already been commented, that adults responsible for the supervision of children and adolescents have the qualification and competence sufficient to give the most precise instructions on the correct technique of exercises, the appropriate behavior in training, and the prescription of the whole training as often, young people without experience often overestimate their physical capacities thus increasing the risk of injury.23 In addition, it is recommended that the ratio between trainer/professor and athletes/alumnos be relatively low (1:10), thus ensuring sufficient feedback in quality and frequency59. Guidelines for the Limitation of Force Training Specialized literature points out that, although a combination or optimal dosage of the components or variables of the load is not known, they can maximize or favor adaptations in response to the training of force at early ages23, general guidelines can be given regarding the components or variables that help to progressively manipulate these throughout the process of physical-sport preparation. Similarly, it should be understood that young people with more force training experience will need to follow periodized training programs with a systematic variation of intensity, volume and speed of execution, to facilitate continuous adaptation and reduce boredom and the risk of overload injuries.15,29. As muscle strength and motor skills dominance improve, the load and complexity of the prescribed training program should reflect the training experience, age and technical abilities of children.15 For all this, the variables of the exercise dose used to program the strength trainings should be carefully controlled with the purpose of safeguarding safety, adherence and ensuring the attainment of the objectives proposed in each phase60. Training Frequency Most well-designed studies, which have shown strength improvements, have used an average frequency of 2.7 ± 0.8 sessions a week in alternate days19. Therefore, the general recommendation for children and adolescents who are starting in force training is 2-3 sessions per week in non-consecutive days, which will allow a proper recovery between sessions while it will be an effective frequency to improve force5-9.48. However, the frequency of training can be increased as children go through adolescence and approach adulthood, especially in those who compete in sports with high strength demands.29 In any case, such frequency should always allow the proper recovery between sessions to avoid overtraining and allow the optimal natural physical development, without forgetting also the rest of weekly training sessions of another kind that the young person may be combining. Training volume The general recommendation, for young subjects without previous force training experience, is to initially perform 1-2 series per exercise7,8,16. As training experience is acquired we can progress to complete 3-4 series per exercise7,8,16. The condition that should always be met will be able to maintain proper technical competence, during each and every series and repetitions performed, before increasing this component of the training dose. For this reason, it is key that the supervisory technician provides frequent feed-back during the execution of the most complex exercises. Regarding the number of exercises per training session, and considering that there should be a balanced distribution for the entire body, it is recommended to make 3-8 exercises per session according to the characteristics of the exercises, training objective and level of accumulated training experience7. In any case, it is necessary that the increases in the training volume be performed carefully, with respect to the individual tolerance of the stress of each child, to avoid overload symptoms and/or acute injuries20. On the other hand, most young people perform whole body workouts several times a week, involving multiple exercises that stress all major muscle groups in each session7. Therefore, on the relationship between the number of exercises depending on the body regions on which the exercises are to be distributed, we recommend that generally global sessions be held (i.e., to allow the training of all the major muscle groups in the same session by means of motric actions of push and traction involving the upper and/or lower hemisphere). Training Intensity When scientific literature refers to the force training intensity component it can do so in relation to different indicators. Traditionally, when it is made according to 1% MRM, the recommendation for children and adolescents is that those young people who are more disenfranchised use resistances less than or close to 60% of the 1RM, while as they accumulate experience and technical competence, they can slowly increase the intensity by using resistances of 70-85% 1MR7.8. Behringer et al.20 comment, as a result of their meta-analysis on the effect of force training on motor performance of motor skills, that the "minimum threshold" to achieve such effects on children and adolescents is about 50% of the 1RM, although these authors and others point out that such a threshold or minimum dose will be different between trained and dissenting subjects15. Only once the exercise in question, with sufficient technical competence, with low-to-moderate loads, can resistance be gradually increased according to the training objectives and individual needs.15 However, using the % 1RM parameter (real or estimated) to determine the training intensity can be unnecessary7,8, as it can be programmed according to appropriate repetition strips and establish the maximum weight to handle for the belt correctly and safely. Once the number of repetitions established with sufficient security and technical quality is made, the weight can be increased by approximately 5 to 1007.14, so that the weight increase is always a consequence of the technical improvements and the application of force in the exercise in question. It is also important to note that not all exercises need to be performed with the same number of repetitions and series7,8,16, so that, for traditional multi-articular and mono-articular exercises, it would be recommended to make between 6-15 repetitions (v. g.: squat, press bench, biceps curl), while for exercises with high output of power and speed (olympic elevations and variants, 6 In all cases, goals and levels of young subjects, it would never be recommended to make the maximum possible number of repetitions per series, so the nature of the effort will always be low61. Exposing children and adolescents to excessive intensities at the expense of the correct technique can lead to acute injuries, while prescribing an excessive volume of training along a training block can induce a state of overtraining8. It will always be better to underestimate the physical abilities of the child than to overestimate them and risk negative consequences such as injury.16 Another type of markers to control the intensity of force training, of great utility and good indices of validity and reliability, are the scales of perceived effort or perception of effort (RPE). There are 2 studies that have developed and validated specific scales with populations of children and adolescents. The first of these studies is the one developed by Faigenbaum et al.62, which, using a sample of 26 children in total of 7-12 years, used an external resistance in the press banking and leg press exercises in machines corresponding to 35, 55, and 75% of the 1RM with which a series of 10 repetitions were made for each resistance. A positive and linear correlation was found between 1 % MR and the perceived effort on a scale of 11 points (r = 0.70-0.77), so it was considered that this scale provided partial validation evidence for child force training. The following year of this publication, Robertson et al.63 validated another scale of effort perceived for force training with a sample of 25 children and 25 girls of years. In this study the authors used an external resistance corresponding to 50% 1RM, with which 3 series of 6, 10 and 14 repetitions were performed respectively for the biceps curl exercises and extension of knees on machine. They found some coefficients of validity through high linear regression (r = 0.72-0.88), which made them conclude that such a perceived scale of effort was a valid tool for performing force exercises for the upper and lower hemisphere with children and youth of both sexes (fig. 2). Figure 2. Scale of perceived OMNI-RES strength for children. Source: Robertson et al.63 Although these and other studies do not recommend any specific range of intensity for force training in children and youth populations using such scales, the authors of this review suggest that a range of 3-7, at the end of each series, would be a safe and effective recommendation. For example, those subjects without previous experience, whose fundamental objective was to set technical patterns in new exercises, a 3-4 (easy and somewhat easy) belt would be the recommended, while young subjects, with experience and good exercise control, could train with a sense of effort at the end of each series between 5-7 values. Applying this concept, the weight of the exercise, and as such, the total number of repetitions per series would be selected by the child based on a predetermined target RPE training area63. Execution speed The use of the same % of 1RM or a certain number of repetitions per series can result in different intensity depending on whether the speed of execution and power produced in each repetition is or not the maximum possible61. Therefore, the speed of execution and the mechanical power produced is another determining indicator for the control and valuation of the intensity of the strength training. The speed is in relation to the acceleration that the neuromuscular system applies to the given resistance, so at higher speed achieved, in the face of the same resistance, greater power produced and therefore will result in a greater intensity or applied strength effort61. On this, the general typical recommendation is that, during the technical learning phases of new exercises, especially in young subjects without experience, control is facilitated and the correct technical execution is ensured through moderate speeds and low loads6-8,29. However, once the subject shows good control and execution of the exercise by the accumulated experience, it must be promoted that intentionality is to perform every repetition as fast as possible, to increase neuromuscular adaptations (increase of recruitment, synchronization and discharge frequencies of motor units)8.29. The development of high-speed movements can be especially important during the years of growth, when neural plasticity and motor coordination are more sensitive to be modified8. Similarly, not all exercises require to be performed at the same speed, as those with higher power production, such as sequential and pliometric exercises, should be performed at high/explosive speeds, while other exercises may be performed at a lower speed7,8,29. Training Density and Inter-Series Recovery Inter-Series Density of training expresses the relationship between the length of effort and the length of the recovery or rest pause60. The length of the recovery interval is an important variable to maintain applied strength levels, speed and power in each movement60. There is evidence that children and adolescents recover more quickly between high-intensity intermittent efforts than adults64-66, so it is suggested that, with moderate-intensity exercises in inexperienced subjects, an approximate minute of recovery between series could be sufficient, for most children and adolescents7,8,29,48. However, the recovery period should probably be increased beyond 2-3 minutes, as the training intensity increases in young experts, such as for example when performing exercises with high strength, power, and technical demand (e.g., Olympic or sequential exercises, and pliometric)7,8,29. Means of training, type and order of exercises Different means or equipment used for exercises have shown to be effective to improve the performance of force in populations of children and adolescents (body weight, elastic bands, adapted variable resistance machines, free weights, manual resistance and medicinal balls)7,8,29,48. It seems reasonable to gradually progress from the simplest exercises, more about jbhnews.com in situations of greater external stability - such as the exercises performed with plate machines-, towards relatively unstable and more complex exercises - such as those performed with free weights or medicinal balls - to improve performance and reduce boredom, as technical competition and confidence improve16,67. It should not be forgotten that the variety of exercises, in the session and over time, is an important element in motivating and preventing boredom at these ages. In the end, the selection of the type of exercise will depend on the technical competence, training objective, anthropometric measures of the child or adolescent and on the resources available. In all cases the priority will be to set correct technical patterns, in variety of exercises with low resistances, both mono and multi-articulars and Olympic upheavals68. Remember again that childhood is considered a crucial period to develop sufficient driving competition, as during these years neuromuscular coordination is more susceptible to change8,29. Likewise, the exercises selected for the session should allow a shared involvement of the main muscle groups of the whole body, in a balanced way (agonist-antagonist muscle balance)7,8. Special attention will deserve those specific exercises for stabilizing musculature of the trunk or chore7,8,29,67. With regard to the order of execution of the exercises in the training session, as well as for adult populations, it is recommended to begin first with those exercises of greater demand or technical complexity and power production (v. g.: Olympic uprisings or sequential and pliometric exercises). Similarly, those exercises for large and central muscle groups should be performed first, before the exercises for small and peripheral muscle groups, or what the same means, to perform the exercises that demand a greater number of muscle groups, to be polyarticular, rather than mono-articulars7. However, the order of exercises must be organized according to the objectives pursued, while those exercises that are being learned must always be done without fatigue and therefore will be at the beginning of the 60th session. Training Methodology The realization of the specific training method, for each training unit or session, should be considered as an independent component of the exercise dose. Scientific literature does not make any specific reference or recommendation on this point, for the training of force at early ages. However, some intervention studies have used vertical progressions, with circular organizations, to check the effect of force exercise (55-70% 1RM) with positive results on body fat, muscle strength and vascular function in obese adolescents.42 This means that vertical methodological progressions, such as the classic "general circles", may be appropriate for children and youth populations with little experience, and there is no need to use horizontal-type progressions in the early stages of formation (Table 1). Table 1. Proposal of force training doses for children and adolescents according to level of experience * Relationship between the number of repetitions performed by series (out of the parenthesis) with respect to the maximum realizable/capable of being performed (between parentheses) in that same exercise, with the same weight and at the same time. Exercise.: exercises. Monkey/Multiart.: Monkey/Multiarticular. Final Recommendations for Practice  • Starting each session with appropriate dynamic warming of 5-10 minutes, including a general part of low-intensity aerobic activities, followed by a specific part with dynamic movements. • Prioritize global or multi-articular exercises with the purpose of improving coordination and balance aspects. In addition, this type of exercise presents mechanical similarities with many sporting gestures that could favor the required performance. • Consider, the training of strength at these ages, as a prophylactic medium of overload injuries, by being able to help compensate for muscle imbalances of the joint of the shoulder and the trunk (core). • Avoid or minimize exercises that involve excessive burden or compressive stress and cizalla for the spine. • Teach the appropriate technique of each exercise with good execution models and proper instruction for learning (low coach-student ratio). • To ensure that the environment and equipment used for exercises are safe and adapted to the anthropometric measures of the child or adolescent, at their level of physical fitness and at their level of technical competence. • Progress with the volume and intensity of training gradually, but enough to allow an effective stimulus. Always use the minimum dose of profitable exercise (effective). • Some articular nuclei have a decrease in the threshold of stress tolerance at structural level, in certain joint actions or critical angles69. This could pose a serious risk to the integrity of such joints, shoulder case and lumbar column, if the exercises were performed throughout the possible joint range69. • Regularly vary the characteristics of weekly training (exercise, media, etc.), to encourage motivation and avoid boredom. Conclusions There is no scientific evidence to show that the training of force, properly supervised and prescribed, may be contraindicated in early ages. On the contrary, it can be a safe, healthy and effective form of training, provided certain safety guidelines and More inspiring ideas criteria are respected. The previous medical-sportal examination, with special attention to the assessment of osteo-articular maturity, is another precautionary measure, related to the state of health, which should be considered. However, the risk of injury, due to the practice of force training, is not greater - even less - than in other sports activities usually practiced. Strength training, at these ages, should contemplate and cover the following objectives: 1) to promote optimal and balanced muscle-skeletal and posture development of the whole body, 2) to consolidate correct technical patterns in variety of exercises with sub-maximum resistances, and 3) to promote and inculcate healthy (active) and lasting lifestyles in adulthood. Also, the training of force at early ages should be progressively incorporated and part of a broader global physical fitness program. 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