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J Biomed 2018; 3:32-39. doi:10.7150/jbm.25035 This volume Cite

Review

Resistance Training in Youth - Benefits and Characteristics

Clemens Drenowatz¹ , Klaus Greier^2,3

1. University of Education, Upper Austria, Division of Physical Education, Linz, Austria
2. Private Educational College - Edith Stein, Division of Physical Education, Stams, Austria
3. Leopold-Franzens-University Innsbruck, Institute for Sports Science, Austria

✉ Corresponding author: Clemens Drenowatz, University of Education Upper Austria, Division of Physical Education, Kaplanhofstraße 40, 4020 Linz, Austria. e-mail: clemens.drenowatzat; Phone: +43 (0)732 / 7470-7426

Abstract

Insufficient physical activity (PA) is one of the major health risks in the 21^st century. Along with secular trends of lower PA in youth there have been significant declines in muscular fitness over the last decades. PA recommendations, nevertheless, focus predominantly on aerobic exercise. Despite research showing no harm or increased injury risk with resistance exercise there remain concerns about the implementation of resistance training in youth. Properly administered resistance training, however, has been associated with lower injury risk compared to various other physical activity youth generally engage in. Resistance training has also been shown to provide important complementary health benefits to aerobic exercise. In addition to beneficial effects on muscular strength and power, resistance training has been associated with increased bone mineral density, reduced risk for chronic disease markers and improved psychological well-being. Resistance training further appears to facilitate a sustainable participation in various physical activities. Even though hypertrophic effects may be limited in children, relative strength gains have been similar between children, adolescents and adults. The utilization of adult resistance training programs, however, is not applicable in youth. Ensuring postural balance along with proper exercise technique are crucial components of resistance training in youth. In addition, individual needs and maturational readiness need to be considered in developing age appropriate resistance training programs that will promote a sustainable participation in PA throughout youth and into adulthood.

Keywords: children, adolescence, strength training, resistance exercise, active lifestyle, chronic disease risk

Introduction

Physical activity (PA) is an important contributor to the physical and psychological development and to the future health status in children and adolescents [1-3]. Nevertheless, a majority of youth reports insufficient PA levels [4, 5], which is accompanied by declining levels of physical fitness worldwide [6-11]. Deficiencies in muscular fitness have been suggested to contribute to low PA levels [12]. Current PA recommendations, however, focus predominantly on aerobic activities (i.e. minimum of 60 min/day of moderate-to-vigorous PA (MVPA) in youth) [13, 14]. The incorporation of muscle strengthening activities, subsequently referred to as resistance training (RT), is only addressed briefly even though poor muscle strength has been associated with increased cardiovascular disease risk in adolescents [15] as well as lower participation in sports and recreational activities [16-18].

RT consists of a variety of resistive loads that are introduced in a progressive manner to improve muscular strength and athletic performance [19]. It has been shown to provide important complementary benefits to MVPA [3, 20] (Table 1). In addition to increased muscle strength, power and motor skill performance [21], participation in RT has been associated with reduced central adiposity and unhealthy weight gain [22], cardiovascular and metabolic diseases [23-25], increased skeletal health [26, 27], as well as reduced risk for fractures and sports-related injuries [20, 28], independent of aerobic fitness [19]. There are also beneficial effects of RT on academic performance [26, 29] and psychological well-being [20, 30-32]. Specifically, RT has been associated with improved physical self-perception [33-35], perceived competence [33, 34], overall self-worth [36] and global self-esteem [37]. As self-perception and self-concept are associated with an individual's motivation towards and engagement in PA, this may have important implications for sustainable participation in various forms of PA [38, 39]. Furthermore, muscular fitness has been shown to track into adulthood [40], and, therefore, can provide a strong foundation for a sustainable active lifestyle. Due to the non-linear relationship between muscular fitness and various health indicators, greatest benefits with RT have been observed in participants with lowest muscular fitness levels [23, 41]. Further, overweight youth experienced the most distinct benefits with RT [23].

Various statements from professional organizations have clarified that participation in appropriate RT improves overall health in youth rather than adversely affect the development of children and adolescents [19, 43-45]. There is also no scientific evidence that properly administered RT adversely affects linear growth during youth or results in reduced height attained in adulthood [19, 46-48]. Nevertheless, there remain concerns regarding the implementation of RT in pediatric populations as it is commonly considered inappropriate or unsafe for children and adolescents [49]. Even though, there is some inherent risk for musculoskeletal injuries with RT, as with any other form of PA, this risk is no greater than that of many other recreational activities or sports youth generally participate in [19]. In fact, properly administered RT programs may actually reduce injury risk during various physical activities in children [20, 50] while providing a variety of health benefits [20, 21, 50-52]. Childhood and adolescence have been suggested as the opportune time to induce beneficial adaptations in bone development due to synergistic effects of mechanical stress induced by RT and growth-related increase in bone mass [27, 43, 46, 47, 53-55]. Furthermore, RT, including plyometric exercises, has been shown to enhance movement biomechanics and functional abilities, which reduces the risk for sports-related injuries in young athletes [56-58]. Accordingly, a prospective study examining 1576 injuries in youth showed lower injury rates with RT compared to football, basketball or soccer [59]. In adolescents, RT has been shown to be markedly safer than many other common sports and physical activities [60]. Most injuries associated with RT in youth are due to lack of or improper instruction and supervision [21] and, therefore, could be avoided with age-appropriate training programs. Nevertheless, almost one third of a representative sample of Dutch parents stated that they would not allow their 12- to 15 year-old offspring to participate in RT due to concerns about the impact on linear growth, while only 4% would prohibit participation in aerobic exercise [49]. Physical education programs also focus predominantly on team sports, and provide only limited exposure to RT [61]. Accordingly, only a small number of young people report regular participation in RT [62] and only a few adolescents appear to be competent in RT skills [63].

Engagement in RT at younger ages may also positively affect behavioral choices in adulthood [64-66] as PA habits are established early in life and muscular strength and RT have been shown to positively affect overall PA in adults [67, 68]. In addition, the intermittent nature of RT has a greater resemblance with youth's habitual PA compared to prolonged continuous exercise. Continuous activities, traditionally used for aerobic conditioning are often considered boring or discomforting [69]. It should further be considered that children with excess body weight can often not compete with their normal weight peers in aerobic exercises [19] and are only able to engage in low intensity continuous exercises due to their low aerobic fitness level [70]. This potentially negatively affects self-efficacy resulting in a vicious cycle of disengagement from PA and increased body weight [71], contributing to further declines in physical fitness. Weight bearing activities such as jogging may also increase the risk of musculoskeletal overuse injuries, particularly in youth with excess body weight [19]. RT, on the other hand, may be better tolerated and appears to be more enjoyable compared to continuous aerobic exercise [72, 73]. As overweight/obese youth are more likely to achieve similar or even better performance during RT compared to their normal weight peers [74] it increases their perceived competence and subsequently the autonomous motivation for PA. A regular participation in RT may further result in beneficial changes in body composition due to increased muscle mass [72], which facilitates participation in various physical activities supporting an overall active lifestyle [21, 75]. Accordingly, pretreatment participation with regular RT has been associated with higher attrition to weight management programs in children [76] while endurance-based exercise interventions are commonly associated with poor compliance due to insufficient motivation for prolonged continuous exercise in children [77]. It should also be mentioned that participation in RT resulted in similar socialization and mental discipline as participation in team sports [78]. Further, it has been argued that PA promotion programs should put a stronger emphasis on what children like to do, rather than what they should do [71]. Accordingly, RT may provide a viable option for a sustainable improvement in PA in youth.

Adaptations to Resistance Training in Youth

When basic principles of design and safety are followed, RT is associated with various beneficial adaptations contributing to increased muscular strength and improved health [50, 79-82]. Increased muscular strength is the result of alterations in architectural (muscle cross-sectional area and size, moment arm length) and neural adaptations [83]. During childhood and adolescence strength gains are also due to growth and maturation [84-86] and these changes potentially mask training effects in case of suboptimal straining stimuli [87, 88]. As indicated by the specific adaptation to imposed demands (SAID) principle, adaptations to RT are specific to the demands of the task, including movement pattern, velocity of movement, contraction type and contraction force [89]. Strength gains in children appear to be predominantly related to neural mechanisms rather than hypertrophic factors due to the lower levels of circulating testosterone that stimulate increases in muscle size [46, 84, 90, 91]. Specifically, a trend toward increased motor unit activation and changes in motor unit coordination, recruitment and firing rate along with increased twitch torque have been suggested to contribute primarily to increased muscular strength. In addition, a transition of type II fibers towards a more glycolytic profile has been suggested [92]. Improvement in inter-muscular coordination also appears to play a significant role as improvement in strength in response to RT is more pronounced than changes in neuromuscular activation [90, 91]. These adaptations along with a higher neural plasticity at younger ages may explain the greater training-induced gains in various strength-related motor skills (e.g. jumping, throwing) of children compared to adolescents [93].

Earlier studies also indicated increased muscle mass with RT even in prepubescent youth [94], which could be attributed to increased testosterone levels and free androgen index values due to alterations in hypothalamic-pituitary-gonadal axis [82]. These alterations may also contribute to beneficial changes in bone mass given the strong association between bone mass and lean body mass [26]. Changes in muscle mass, however, will become more apparent after puberty [94, 95]. Particularly males experience pronounced gains in lean body mass and cross-sectional area in response to RT during late adolescence [93]. Females experience less hypertrophy due to lower testosterone levels [86]. Alterations in growth-hormone and insulin-like growth factors, however, still contribute to muscle growth in females [96]. More pronounced hypertrophic effects of RT result in greater absolute strength gains in adolescents compared to children [97]. Relative strength gains, however, appear to be similar between children, adolescents and adulths [81, 86, 98]. RT lasting between 8 and 20 weeks has been associated with average strength gains between 30% and 40% [19] with maximum strength gains of up to 90% [97]. The variability in response to RT can at least partially be explained by differences in training volume, intensity, frequency, duration, type of training along with quality of supervision [99].

The previously described qualitative and quantitative changes in muscle tissue have also been associated with a risk reduction for various chronic diseases due to beneficial alterations in insulin sensitivity, lipid profile, blood pressure and abdominal fat in adults [100-103]. Even though clinical symptoms of cardiovascular disease may not become apparent until adulthood, some of these risk factors already occur in early childhood [104]. Further, a clustering of chronic disease risk factors observed during childhood has been shown to persist into adulthood [105]. Particularly overweight and obese children have shown favorable changes in body composition and insulin sensitivity with RT, which was attributed to qualitative changes in skeletal muscle [24, 52, 74, 106, 107]. Further, the previously addressed beneficial adaptations in bone development could reduce the risk for osteoporosis and associated fractures later in life [108]. One of the greatest benefits of RT in youth, however, may be the improvement in selected motor skills [93], which is associated with increased perceived competence that increases motivation towards PA [3]. Greater enjoyment with participation in various sports and physical activities would also facilitate a more active lifestyle during adulthood [20].

Characteristics of Resistance Training in Youth

Despite the fact that youth experience comparable benefits in response to RT as adults, it would be a mistake to submit children and adolescents to an adult training program [19]. RT in youth requires careful and evidence-based exercise prescription that considers the specific needs, goals and interests of the participants along with their physical and psychological uniqueness (e.g. training age, technical competency, maturation). Table 2 displays seven fundamental principles, summarized by the acronym PROCESS, that should be considered in order to provide safe and effective RT programs. There are no minimum age requirements for participation in RT and noticeable improvements in muscular fitness following RT have been shown in children as young as 5 to 6 years [109-111]. In order to successfully and safely implement RT, children, however, need to be emotionally mature enough to accept and follow directions and display competency in balance and postural control [19, 112]. Participants need to be familiar with basic exercise etiquette including handling and storage of exercise equipment. Further, individual and realistic goal setting should be part of any RT program [19]. Given these requirements, 7- to 8-year-old children should generally be able to safely participate in RT [113]. Further, a year-round participation in RT should be encouraged. Short training programs followed by longer periods of detraining provide only limited health benefits due rapid decline of the initial gains in neuromuscular activation and motor coordination [114-117].

There appears to be no single optimal combination of exercises, sets and repetitions to induce beneficial adaptations in youth [21]. A variety of RT programs including free weights, weight machines, medicine balls, elastic bands and body weight exercises have been shown to provide beneficial outcomes [19]. Accordingly, a systematic and sensible variation in exercise selection and alterations in intensity, volume and frequency of repetitions should be employed in order to facilitate a sustainable participation in RT and reduce the risk of overuse injuries [118]. Body size, training age and fitness levels need to be considered as well when selecting exercises. Less experienced participants should start with relatively simple movements and gradually progress towards more advanced multi-joint exercises [21]. Given the differences in adaptations, RT in children should predominantly focus on strength gains due to function and motor control rather than increased muscle size, which becomes more pronounced during adolescence. Such an approach requires an emphasis on movement technique at the appropriate movement speed rather than pushing for high exhaustion. Any exercise program should include warm-up and cool-down along with information on selection and order of exercises, training intensity and volume, movement velocity and rest intervals (Table 3).

RT prescriptions are commonly based on the maximum load that can be moved one time (one-repetition maximum, 1RM). With qualified supervision to ensure proper technique along with participation in a habituation period before testing, healthy children and adolescents have been shown to be able to safely engage in 1RM testing [19]. Several common field tests (e.g. long jump, handgrip strength), however, also provide viable information on force capacity in youth and correlate with 1RM [119]. When starting an RT program, light loads (≤ 60% 1RM) and simpler movements to learn the proper exercise technique should be used. Subsequently intensity, complexity of exercises and movement speed can gradually be increased [118]. Each exercise session should address all major muscle groups and exercise selection should promote muscle balance across joints to ensure equal development of opposing muscles. More challenging exercises such as multi-joint exercises should be performed early in the training session when there is less fatigue in the neuromuscular system. While up to 15 repetitions per set can be performed for strength exercises, fewer than 6 to 8 repetitions are generally recommended when performing more intense power exercises (e.g. plyometrics) [19, 21]. Rest intervals between sets can be shorter in children as they have been shown to recover more quickly from RT than adolescents and adults (about 1 minute compared to 2-3 minutes in adults) [120-122]. Due to increased pliability of muscle tissue youth are also less likely to experience muscle damage and delayed onset of muscle soreness [123]. Nevertheless, strength training sessions are not supposed to be performed on consecutive days. In addition to the actual training protocol, the importance of proper nutrition along with sufficient hydration and adequate sleep should be addressed as well [20].

Summary and Conclusion

Insufficient PA in youth is becoming a major threat to public health. It not only affects immediate health and well-being but also has important implications in later life [124]. Given the consistent and measureable decrements in muscular fitness in youth over the last decade [7, 10] RT should be recognized as important component in the promotion of an active lifestyle [89]. While there remain reservations about the implementation of RT in youth, research has not shown any detrimental effects of RT on growth and development in youth; rather RT appears to be a safe, effective and worthwhile form of exercise for children and adolescents. Lack of participation in RT in early life may actually increase the risk for negative health outcomes later in life [20]. In addition to improved muscular fitness and motor skills, RT has been associated with increased bone mineral density, improved body composition, reduced risk for cardiovascular and metabolic diseases, as well as increased perceived competence and general psychological well-being [3, 20, 21, 40]. These benefits, however, only occur with sustainable participation in RT.

Prescription of RT requires an individual approach that considers training age, current strength level, motor skill competency as well as psychological and maturational readiness. Emphasizing proper technique not only ensures safety; it also promotes motor competence in foundational skills that facilitate participation in a variety of sports and physical activities. At this time there is no single best RT program for youth and various exercises, including own body-weight, free weights, weight machines and elastic bands, among others should be implemented. Accordingly, more research is needed to clarify exercise selection in RT (frequency, volume, intensity) regarding specific adaptations in children and adolescents. The utilization of a broad range of exercises in RT programs may actually be a crucial component in itself as it increases the likelihood for sustained motivation towards engagement in RT along with the reduction of injury risk. RT has also been associated with positive attitudes towards PE and lifelong exercise [125] which could facilitate a sustainable increase in PA throughout childhood, adolescence and adulthood [126]. As insufficient PA has been identified as one of the leading threats to future public health [14], RT should be considered a viable intervention strategy in the promotion of an active lifestyle.

Competing Interests

The authors have declared that no competing interest exists.

References

1. Janssen I, Leblanc AG. Systematic review of the health benefits of physical activity and fitness in school-aged children and youth. Int J Behav Nutr Phys Act. 2010;7:40

2. Lubans D, Richards J, Hillman C, Faulkner G, Beauchamp M, Nilsson M, Kelly P, Smith J, Raine L, Biddle S. Physical Activity for Cognitive and Mental Health in Youth: A Systematic Review of Mechanisms. Pediatrics. 2016:138 (3)

3. Smith JJ, Eather N, Morgan PJ, Plotnikoff RC, Faigenbaum AD, Lubans DR. The health benefits of muscular fitness for children and adolescents: a systematic review and meta-analysis. Sports Med. 2014;44(9):1209-1223

4. Institute of Medicine. Educating the student body: Taking physical activity and physical education to school. Washington, D.C.: The National Academic Press. 2013

5. Townsend N, Wickramasinghe K, Williams J, Bhatnagar P, Rayner M. Physical Activity Statistics 2015. London: British Heart Foundation. 2015

6. Tomkinson GR, Léger LA, Olds TS, Cazorla G. Secular trends in the performance of children and adolescents (1980-2000): an analysis of 55 studies of the 20m shuttle run test in 11 countries. Sports Med. 2003;33(4):285-300

7. Cohen DD, Voss C, Taylor MJ, Delextrat A, Ogunleye AA, Sandercock GR. Ten-year secular changes in muscular fitness in English children. Acta Paediatr. 2011;100(10):e175-177

8. Moliner-Urdiales D, Ruiz JR, Ortega FB, Jiménez-Pavón D, Vicente-Rodriguez G, Rey-López JP, Martínez-Gómez D, Casajús JA, Mesana MI, Marcos A. et al. Secular trends in health-related physical fitness in Spanish adolescents: the AVENA and HELENA studies. J Sci Med Sport. 2010;13(6):584-588

9. Tomkinson G, Olds T. Secular changes in pediatric aerobic fitness test performance: the global picture. Basel: Karger Publishers. 2007

10. Runhaar J, Collard DC, Singh AS, Kemper HC, van Mechelen W, Chinapaw M. Motor fitness in Dutch youth: differences over a 26-year period (1980-2006). J Sci Med Sport. 2010;13(3):323-328

11. Matton L, Duvigneaud N, Wijndaele K, Philippaerts R, Duquet W, Beunen G, Claessens AL, Thomis M, Lefevre J. Secular trends in anthropometric characteristics, physical fitness, physical activity, and biological maturation in Flemish adolescents between 1969 and 2005. Am J Hum Biol. 2007;19(3):345-357

12. Faigenbaum A, McFarland J. Resistance training for kids: right from the start. ACSM's Health and Fitness Journal. 2016;20(5):16-22

13. U.S. Department of Health and Human Services. 2008 physical activity guidelines for Americans [http://www.health.gov/paguidelines/guidelines/].

14. World Health Organization W. Global recommendations on physical activity for health. In. Geneva, Switzerland: WHO Press. 2010

15. Steene-Johannessen J, Anderssen SA, Kolle E, Andersen LB. Low muscle fitness is associated with metabolic risk in youth. Med Sci Sports Exerc. 2009;41(7):1361-1367

16. Lopes VP, Rodrigues LP, Maia JA, Malina RM. Motor coordination as predictor of physical activity in childhood. Scand J Med Sci Sports. 2011;21(5):663-669

17. D'Hondt E, Deforche B, Vaeyens R, Vandorpe B, Vandendriessche J, Pion J, Philippaerts R, de Bourdeaudhuij I, Lenoir M. Gross motor coordination in relation to weight status and age in 5- to 12-year-old boys and girls: a cross-sectional study. Int J Pediatr Obes. 2011;6(2-2):e556-564

18. D'Hondt E, Deforche B, Gentier I, De Bourdeaudhuij I, Vaeyens R, Philippaerts R, Lenoir M. A longitudinal analysis of gross motor coordination in overweight and obese children versus normal-weight peers. Int J Obes (Lond). 2013;37(1):61-67

19. Faigenbaum AD, Kraemer WJ, Blimkie CJ, Jeffreys I, Micheli LJ, Nitka M, Rowland TW. Youth resistance training: updated position statement paper from the national strength and conditioning association. J Strength Cond Res. 2009;23(5 Suppl):S60-79

20. Lloyd RS, Faigenbaum AD, Stone MH, Oliver JL, Jeffreys I, Moody JA, Brewer C, Pierce KC, McCambridge TM, Howard R. et al. Position statement on youth resistance training: the 2014 International Consensus. Br J Sports Med. 2014;48(7):498-505

21. Faigenbaum AD, Myer GD. Pediatric resistance training: benefits, concerns, and program design considerations. Curr Sports Med Rep. 2010;9(3):161-168

22. Artero EG, España-Romero V, Jiménez-Pavón D, Martinez-Gómez D, Warnberg J, Gómez-Martínez S, González-Gross M, Vanhelst J, Kafatos A, Molnar D. et al. Muscular fitness, fatness and inflammatory biomarkers in adolescents. Pediatr Obes. 2014;9(5):391-400

23. Artero E, Ruiz J, Ortega F, Espana-Romero V, Vicente-Rodriguez G, Molnar D, Gottrand F, Gonzalez-Gross M, C B, LA M. et al. Muscular and cardiorespiratory fitness are independently associated with metabolic risk in adolescents: the HELENA study. Pediatr Diabetes. 2011;12(8):704-712

24. Shaibi GQ, Cruz ML, Ball GD, Weigensberg MJ, Salem GJ, Crespo NC, Goran MI. Effects of resistance training on insulin sensitivity in overweight Latino adolescent males. Med Sci Sports Exerc. 2006;38(7):1208-1215

25. Benson AC, Torode ME, Singh MA. Muscular strength and cardiorespiratory fitness is associated with higher insulin sensitivity in children and adolescents. Int J Pediatr Obes. 2006;1(4):222-231

26. Vicente-Rodríguez G, Urzanqui A, Mesana MI, Ortega FB, Ruiz JR, Ezquerra J, Casajús JA, Blay G, Blay VA, Gonzalez-Gross M. et al. Physical fitness effect on bone mass is mediated by the independent association between lean mass and bone mass through adolescence: a cross-sectional study. J Bone Miner Metab. 2008;26(3):288-294

27. Bass SL. The prepubertal years: a uniquely opportune stage of growth when the skeleton is most responsive to exercise?. Sports Med. 2000;30(2):73-78

28. Behringer M, Gruetzner S, McCourt M, Mester J. Effects of weight-bearing activities on bone mineral content and density in children and adolescents: a meta-analysis. J Bone Miner Res. 2014;29(2):467-478

29. Coe DP, Pivarnik JM, Womack CJ, Reeves MJ, Malina RM. Health-related fitness and academic achievement in middle school students. J Sports Med Phys Fitness. 2012;52(6):654-660

30. Lubans DR, Smith JJ, Morgan PJ, Beauchamp MR, Miller A, Lonsdale C, Parker P, Dally K. Mediators of Psychological Well-being in Adolescent Boys. J Adolesc Health. 2016;58(2):230-236

31. Faigenbaum AD, Myer GD. Resistance training among young athletes: safety, efficacy and injury prevention effects. Br J Sports Med. 2010;44(1):56-63

32. Padilla-Moledo C, Ruiz JR, Ortega FB, Mora J, Castro-Piñero J. Associations of muscular fitness with psychological positive health, health complaints, and health risk behaviors in Spanish children and adolescents. J Strength Cond Res. 2012;26(1):167-173

33. Morano M, Colella D, Robazza C, Bortoli L, Capranica L. Physical self-perception and motor performance in normal-weight, overweight and obese children. Scand J Med Sci Sports. 2011;21(3):465-473

34. Haugen T, Ommundsen Y, Seiler S. The relationship between physical activity and physical self-esteem in adolescents: the role of physical fitness indices. Pediatr Exerc Sci. 2013;25(1):138-153

35. Lubans D, Aguiar E, Callister R. The effects of free weights and elastic tubing resistance training on physical self-perception in adolescents. Psychol Sport Exerc. 2010;11:497-504

36. Lubans DR, Cliff DP. Muscular fitness, body composition and physical self-perception in adolescents. J Sci Med Sport. 2011;14(3):216-221

37. Smith AJ, O'Sullivan PB, Campbell A, Straker L. The relationship between back muscle endurance and physical, lifestyle, and psychological factors in adolescents. J Orthop Sports Phys Ther. 2010;40(8):517-523

38. Altintaş A, Aşçi FH. Physical self-esteem of adolescents with regard to physical activity and pubertal status. Pediatr Exerc Sci. 2008;20(2):142-156

39. Babic MJ, Morgan PJ, Plotnikoff RC, Lonsdale C, White RL, Lubans DR. Physical activity and physical self-concept in youth: systematic review and meta-analysis. Sports Med. 2014;44(11):1589-1601

40. Ortega FB, Ruiz JR, Castillo MJ, Sjöström M. Physical fitness in childhood and adolescence: a powerful marker of health. Int J Obes (Lond). 2008;32(1):1-11

41. Mota J, Vale S, Martins C, Gaya A, Moreira C, Santos R, Ribeiro JC. Influence of muscle fitness test performance on metabolic risk factors among adolescent girls. Diabetol Metab Syndr. 2010;2:42

42. Mühlbauer T, Roth R, Kibele A, Behm D, Granacher U. Krafttraining mit Kindern und Jugendlichen: Praktische Umsetzung und theoretische Grundlagen [Strength training with children and adoescents: Practical application and theoretical foundations]. Schorndorf: Hofmann-Verlag. 2013

43. Behm DG, Faigenbaum AD, Falk B, Klentrou P. Canadian Society for Exercise Physiology position paper: resistance training in children and adolescents. Appl Physiol Nutr Metab. 2008;33(3):547-561

44. Stratton G, Jones M, Fox KR, Tolfrey K, Harris J, Maffulli N, Lee M, Frostick SP, Group R. BASES position statement on guidelines for resistance exercise in young people. J Sports Sci. 2004;22(4):383-390

45. Roberts S, Ciapponi T, Lytle R. Strength training for children and adolescents. Reston, VA: National Association for Sports and Physical Education. 2008

46. Malina RM. Weight training in youth-growth, maturation, and safety: an evidence-based review. Clin J Sport Med. 2006;16(6):478-487

47. Falk B, Eliakim A. Resistance training, skeletal muscle and growth. Pediatr Endocrinol Rev. 2003;1(2):120-127

48. Sadres E, Eliakim A, Constantini N, Lidor R, Falk B. The effect of long-term resistance training on anthropometric measures, muscle strength, and self-concept in pre-pubertal boys. Pediatr Exerc Sci. 2001;13(4):357-372

49. ten Hoor GA, Sleddens EF, Kremers SP, Schols AM, Kok G, Plasqui G. Aerobic and strength exercises for youngsters aged 12 to 15: what do parents think?. BMC Public Health. 2015;15:994

50. Faigenbaum A. Resistance training for children and adolescents: are there health outcomes?. Am J Lifestyle Med. 2007;1:190-200

51. Barbieri D, Zaccagni L. Strength training for children and adolescents: benefits and risks. Coll Antropol. 2013;37(Suppl 2):219-225

52. Benson AC, Torode ME, Fiatarone Singh MA. The effect of high-intensity progressive resistance training on adiposity in children: a randomized controlled trial. Int J Obes (Lond). 2008;32(6):1016-1027

53. Hind K, Burrows M. Weight-bearing exercise and bone mineral accrual in children and adolescents: a review of controlled trials. Bone. 2007;40(1):14-27

54. Vicente-Rodríguez G. How does exercise affect bone development during growth?. Sports Med. 2006;36(7):561-569

55. Gunter KB, Almstedt HC, Janz KF. Physical activity in childhood may be the key to optimizing lifespan skeletal health. Exerc Sport Sci Rev. 2012;40(1):13-21

56. Lephart SM, Abt JP, Ferris CM, Sell TC, Nagai T, Myers JB, Irrgang JJ. Neuromuscular and biomechanical characteristic changes in high school athletes: a plyometric versus basic resistance program. Br J Sports Med. 2005;39(12):932-938

57. Mandelbaum BR, Silvers HJ, Watanabe DS, Knarr JF, Thomas SD, Griffin LY, Kirkendall DT, Garrett W. Effectiveness of a neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes: 2-year follow-up. Am J Sports Med. 2005;33(7):1003-1010

58. Myer GD, Ford KR, Palumbo JP, Hewett TE. Neuromuscular training improves performance and lower-extremity biomechanics in female athletes. J Strength Cond Res. 2005;19(1):51-60

59. Zaricznyj B, Shattuck LJ, Mast TA, Robertson RV, D'Elia G. Sports-related injuries in school-aged children. Am J Sports Med. 1980;8(5):318-324

60. Hamill B. Relative safety of weight lifting and weight training. J Strength Cond Res. 1994;8:53-57

61. Ennis CD. What Goes Around Comes Around … Or Does It? Disrupting the Cycle of Traditional, Sport-Based Physical Education. Kinesiol Rev (Champaign). 2014;3(1):63-70

62. Hulteen RM, Smith JJ, Morgan PJ, Barnett LM, Hallal PC, Colyvas K, Lubans DR. Global participation in sport and leisure-time physical activities: A systematic review and meta-analysis. Prev Med. 2017;95:14-25

63. Smith JJ, DeMarco M, Kennedy SG, Kelson M, Barnett LM, Faigenbaum AD, Lubans DR. Prevalence and correlates of resistance training skill competence in adolescents. J Sports Sci. 2017:1-9

64. Telama R. Tracking of physical activity from childhood to adulthood: a review. Obes Facts. 2009;2(3):187-195

65. Rowland TW. Promoting physical activity for children's health: rationale and strategies. Sports Med. 2007;37(11):929-936

66. Telama R, Yang X, Leskinen E, Kankaanpää A, Hirvensalo M, Tammelin T, Viikari JS, Raitakari OT. Tracking of physical activity from early childhood through youth into adulthood. Med Sci Sports Exerc. 2014;46(5):955-962

67. Drenowatz C, Grieve GL, DeMello MM. Change in energy expenditure and physical activity in response to aerobic and resistance exercise programs. Springerplus. 2015;4:798

68. Braith RW, Stewart KJ. Resistance exercise training: its role in the prevention of cardiovascular disease. Circulation. 2006;113(22):2642-2650

69. Bailey RC, Olson J, Pepper SL, Porszasz J, Barstow TJ, Cooper DM. The level and tempo of children's physical activities: an observational study. Med Sci Sports Exerc. 1995;27(7):1033-1041

70. Owen CG, Nightingale CM, Rudnicka AR, Sattar N, Cook DG, Ekelund U, Whincup PH. Physical activity, obesity and cardiometabolic risk factors in 9- to 10-year-old UK children of white European, South Asian and black African-Caribbean origin: the Child Heart And health Study in England (CHASE). Diabetologia. 2010;53(8):1620-1630

71. Ten Hoor GA, Plasqui G, Ruiter RA, Kremers SP, Rutten GM, Schols AM, Kok G. A new direction in psychology and health: Resistance exercise training for obese children and adolescents. Psychol Health. 2016;31(1):1-8

72. Schranz N, Tomkinson G, Olds T. What is the effect of resistance training on the strength, body composition and psychosocial status of overweight and obese children and adolescents? A Systematic review and meta-analysis. Sports Med. 2013;43(9):893-907

73. Colella D, Morano M, Robazza C, Bortoli L. Body image, perceived physical ability, and motor performance in nonoverweight and overweight Italian children. Percept Mot Skills. 2009;108(1):209-218

74. Sothern MS, Loftin JM, Udall JN, Suskind RM, Ewing TL, Tang SC, Blecker U. Safety, feasibility, and efficacy of a resistance training program in preadolescent obese children. Am J Med Sci. 2000;319(6):370-375

75. Castelli D, Valley J. Chapter 3: The relationship of physical fitness and motor competence to physical activity. J Teach Phys Educ. 2007;26(4):358-374

76. Ehrmann DE, Sallinen BJ, IglayReger HB, Gordon PM, Woolford SJ. Slow and steady: readiness, pretreatment weekly strengthening activity, and pediatric weight management program completion. Child Obes. 2013;9(3):193-199

77. Sothern MS, Hunter S, Suskind RM, Brown R, Udall JN, Blecker U. Motivating the obese child to move: the role of structured exercise in pediatric weight management. South Med J. 1999;92(6):577-584

78. Rians CB, Weltman A, Cahill BR, Janney CA, Tippett SR, Katch FI. Strength training for prepubescent males: is it safe?. Am J Sports Med. 1987;15(5):483-489

79. Faigenbaum AD, McFarland JE, Johnson L, Kang J, Bloom J, Ratamess NA, Hoffman JR. Preliminary evaluation of an after-school resistance training program for improving physical fitness in middle school-age boys. Percept Mot Skills. 2007;104(2):407-415

80. Faigenbaum A, Milliken L, Moulton L, Westcott W. Early muscular fitness adaptations in children in response to two different resistance training regimens. Pediatr Exerc Sci. 2005;17(3):237-248

81. Lillegard WA, Brown EW, Wilson DJ, Henderson R, Lewis E. Efficacy of strength training in prepubescent to early postpubescent males and females: effects of gender and maturity. Pediatr Rehabil. 1997;1(3):147-157

82. Tsolakis CK, Vagenas GK, Dessypris AG. Strength adaptations and hormonal responses to resistance training and detraining in preadolescent males. J Strength Cond Res. 2004;18(3):625-629

83. Bouchant A, Martin V, Maffiuletti NA, Ratel S. Can muscle size fully account for strength differences between children and adults?. J Appl Physiol (1985). 2011;110(6):1748-1749

84. Malina RM, Bouchard C, Bar-Or O. Growth, maturation, and physical activity, 2nd edn. Champaign, IL: Human Kinectics. 2004

85. Beunen G, Malina R. Growth and biologic maturation: relevance to athletic performance. The child and adolescent athlete. edn. Edited by Hebestreit H, Bar-Or O. Oxford: Blackwell Publishing. 2008:3-17

86. Rowland T. Children's Exercise Physiology, 2nd edn. Champaign, IL: Human Kinetics. 2005

87. Naughton G, Farpour-Lambert NJ, Carlson J, Bradney M, Van Praagh E. Physiological issues surrounding the performance of adolescent athletes. Sports Med. 2000;30(5):309-325

88. Matos N, Winsley RJ. Trainability of young athletes and overtraining. J Sports Sci Med. 2007;6(3):353-367

89. Myer GD, Faigenbaum AD, Edwards NM, Clark JF, Best TM, Sallis RE. Sixty minutes of what? A developing brain perspective for activating children with an integrative exercise approach. Br J Sports Med. 2015;49(23):1510-1516

90. Ramsay JA, Blimkie CJ, Smith K, Garner S, MacDougall JD, Sale DG. Strength training effects in prepubescent boys. Med Sci Sports Exerc. 1990;22(5):605-614

91. Ozmun JC, Mikesky AE, Surburg PR. Neuromuscular adaptations following prepubescent strength training. Med Sci Sports Exerc. 1994;26(4):510-514

92. Sale D. Strength training in children. Perspectives in Exercise Science and Sports Medicine. edn. Edited by Gisolfi C, Lamp D. Carmel, IN: Benchmark Press. 1989:165-216

93. Behringer M, Vom Heede A, Matthews M, Mester J. Effects of strength training on motor performance skills in children and adolescents: a meta-analysis. Pediatr Exerc Sci. 2011;23(2):186-206

94. Mersch F, Stoboy H. Strenght training and muscle hypertrophy in children. Children and Exercise XIII. edn. Edited by Oseid S, Carlsen K. Champaign, IL: Human Kinetics. 1989:165-182

95. Fukunaga T, Funato K, Ikegawa S. The effects of resistance training on muscle area and strength in prepubescent age. Ann Physiol Anthropol. 1992;11(3):357-364

96. Kraemer W, Fry A, Frykman P, Conroy B, Hoffman J. Resistance training and youth. Pediatr Exerc Sci. 1989;1:336-350

97. Behringer M, Vom Heede A, Yue Z, Mester J. Effects of resistance training in children and adolescents: a meta-analysis. Pediatrics. 2010;126(5):e1199-1210

98. Payne VG, Morrow JR, Johnson L, Dalton SN. Resistance training in children and youth: a meta-analysis. Res Q Exerc Sport. 1997;68(1):80-88

99. Gentil P, Bottaro M. Influence of supervision ratio on muscle adaptations to resistance training in nontrained subjects. J Strength Cond Res. 2010;24(3):639-643

100. Tresierras MA, Balady GJ. Resistance training in the treatment of diabetes and obesity: mechanisms and outcomes. J Cardiopulm Rehabil Prev. 2009;29(2):67-75

101. Hurley BF, Hanson ED, Sheaff AK. Strength training as a countermeasure to aging muscle and chronic disease. Sports Med. 2011;41(4):289-306

102. Kelley GA, Kelley KS. Impact of progressive resistance training on lipids and lipoproteins in adults: a meta-analysis of randomized controlled trials. Prev Med. 2009;48(1):9-19

103. Kelley GA, Kelley KS. Progressive resistance exercise and resting blood pressure: A meta-analysis of randomized controlled trials. Hypertension. 2000;35(3):838-843

104. McGill HC, McMahan CA, Zieske AW, Tracy RE, Malcom GT, Herderick EE, Strong JP. Association of Coronary Heart Disease Risk Factors with microscopic qualities of coronary atherosclerosis in youth. Circulation. 2000;102(4):374-379

105. Raitakari OT, Juonala M, Kähönen M, Taittonen L, Laitinen T, Mäki-Torkko N, Järvisalo MJ, Uhari M, Jokinen E, Rönnemaa T. et al. Cardiovascular risk factors in childhood and carotid artery intima-media thickness in adulthood: the Cardiovascular Risk in Young Finns Study. JAMA. 2003;290(17):2277-2283

106. Watts K, Beye P, Siafarikas A, Davis EA, Jones TW, O'Driscoll G, Green DJ. Exercise training normalizes vascular dysfunction and improves central adiposity in obese adolescents. J Am Coll Cardiol. 2004;43(10):1823-1827

107. Yu CC, Sung RY, So RC, Lui KC, Lau W, Lam PK, Lau EM. Effects of strength training on body composition and bone mineral content in children who are obese. J Strength Cond Res. 2005;19(3):667-672

108. Hansen MA, Overgaard K, Riis BJ, Christiansen C. Role of peak bone mass and bone loss in postmenopausal osteoporosis: 12 year study. BMJ. 1991;303(6808):961-964

109. Faigenbaum AD, Westcott WL, Loud RL, Long C. The effects of different resistance training protocols on muscular strength and endurance development in children. Pediatrics. 1999;104(1):e5

110. Kaufman LB, Schilling DL. Implementation of a strength training program for a 5-year-old child with poor body awareness and developmental coordination disorder. Phys Ther. 2007;87(4):455-467

111. Annesi JJ, Westcott WL, Faigenbaum AD, Unruh JL. Effects of a 12-week physical activity protocol delivered by YMCA after-school counselors (Youth Fit for Life) on fitness and self-efficacy changes in 5-12-year-old boys and girls. Res Q Exerc Sport. 2005;76(4):468-476

112. American AoP. Strenght training by children and adolescents. Pediatrics. 2008:121 (835-840)

113. Faigenbaum AD, Lloyd RS, MacDonald J, Myer GD. Citius, Altius, Fortius: beneficial effects of resistance training for young athletes: Narrative review. Br J Sports Med. 2016;50(1):3-7

114. Faigenbaum AD, Farrell AC, Fabiano M, Radler TA, Naclerio F, Ratamess NA, Kang J, Myer GD. Effects of detraining on fitness performance in 7-year-old children. J Strength Cond Res. 2013;27(2):323-330

115. Ingle L, Sleap M, Tolfrey K. The effect of a complex training and detraining programme on selected strength and power variables in early pubertal boys. J Sports Sci. 2006;24(9):987-997

116. Blimkie C, Sale D. Strength development during childhood. Paediatric anaerobic performance. edn. Edited by Praag E. Champaign, IL: Human Kinetics. 1998:193-224

117. Faigenbaum A, Wescott W, Micheli L, Outerbridge A, Long C, LaRosa-Loud R, Zaichkowsky L. The effects of strength training and detraining on children. J Strength Cond Res. 1996;10:109-114

118. Ratamess N, Alvar B, Evetoch T, Housh T, Kibler W, Kraemer W, Triplett N. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sports Exerc. 2009;41(3):687-708

119. Milliken LA, Faigenbaum AD, Loud RL, Westcott WL. Correlates of upper and lower body muscular strength in children. J Strength Cond Res. 2008;22(4):1339-1346

120. Zafeiridis A, Dalamitros A, Dipla K, Manou V, Galanis N, Kellis S. Recovery during high-intensity intermittent anaerobic exercise in boys, teens, and men. Med Sci Sports Exerc. 2005;37(3):505-512

121. Faigenbaum AD, Ratamess NA, McFarland J, Kaczmarek J, Coraggio MJ, Kang J, Hoffman JR. Effect of rest interval length on bench press performance in boys, teens, and men. Pediatr Exerc Sci. 2008;20(4):457-469

122. Falk B, Dotan R. Child-adult differences in the recovery from high-intensity exercise. Exerc Sport Sci Rev. 2006;34(3):107-112

123. Eston R, Byrne C, Twist C. Muscle function after exercise-induced muscle damage: Considerations for athletic performance in children and adults. J Exerc Sci Fitness. 2003;1(2):85-96

124. Faigenbaum AD, Myer GD. Exercise deficit disorder in youth: play now or pay later. Curr Sports Med Rep. 2012;11(4):196-200

125. Westcott W, Tolken J, Wessner B. School-based conditioning programs for physically unfit children. Strength Cond J. 1995;17:5-9

126. Telama R, Yang X, Viikari J, Välimäki I, Wanne O, Raitakari O. Physical activity from childhood to adulthood: a 21-year tracking study. Am J Prev Med. 2005;28(3):267-273

Author contact

Corresponding author: Clemens Drenowatz, University of Education Upper Austria, Division of Physical Education, Kaplanhofstraße 40, 4020 Linz, Austria. e-mail: clemens.drenowatzat; Phone: +43 (0)732 / 7470-7426

Received 2018-1-19
Accepted 2018-2-20
Published 2018-2-22

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