Many preconceptions exist about the efficacy and safety of resistance training in preadolescent children. Exercise has been shown to benefit the human body, especially in adolescents and adults, and research in the field of resistance training has indicated a positive correlation with training and increases in muscular strength, bone mineral density, motor coordination, and body composition (3-10,13,15). Preadolescence is a crucial time for the growth and development of the skeleton as well as the muscles and connective tissues that surround it (8). The arguments against resistance training are primarily concerned with the impact that these weight bearing loads have on the growing bones and the safety issues that surround children performing complicated weight lifting techniques (7-9). Stunted growth, decreased strength levels, and epiphyseal plate damage are all concerns that are associated with resistance training in this population (7,8). However, much of the literature that has studied the effect of resistance training in children show a positive impact on bone health and strength development when properly prescribed and supervised (1-10,12-15).

Impact on Bone Mineral Density

Numerous studies have shown a positive correlation between resistance training and increases in areal bone mineral density in children (3,4,7-9). This acquisition of greater bone density early in life appears to carry over into adolescence, suggesting moderate resistance training before puberty may be effective in reducing age-related bone loss and damage (3,4, 7-9). Faigenbaum et al. suggest that participation in sports and resistance training at this age is critical to the remodeling and strengthening of bones that may lead to performance and health benefits in the future (8). Much of the literature concerning the possible negative impact of strength training on growth and development references the reduction in height of young gymnasts; whether or not this is primarily due to the vigorous intensity of gymnastics or selection for specific body types for this sport has not been fully determined, but it’s also hypothesized that this reduction in growth could be due to insufficient nutritional intake that does not match the high energy expenditure experienced in this sport (3).

To study the effects of exercise on bone mineral density, Bass et al. compared prepubertal and retired female gymnasts to control groups matched for skeletal age in the prepubertal group, and age, height, and weight for the retired gymnast group. Areal bone mineral density was found to be 30-85% greater in the prepubertal gymnastics group compared to the control (3). The retired gymnasts also exhibited a higher areal bone mineral density than their matched control group even after 20 years of being removed from the sport (3). Bass et al. findings suggest that this increase in bone mass during there prepubertal years was retained by the gymnasts into adulthood (3). These findings are consistent with previous literature that have noticed a retention of high bone mineral density in retired athletes and weight lifters (3,4,8,9). Bradney et al. found similar results in pre-pubertal boys that had participated in an 8-week, 30 minute, moderately intense weight bearing training session performed 3 days a week. At the conclusion of this study the exercised group exhibited an increase in areal bone mineral density that was double the amount found increased in the control group (4). These increases in bone mineral density appear to be specific to the bones that are involved in the weight bearing aspect of the exercise (3,4). Exercise seems to increase periosteal and endocortical apposition of bone at the weight-bearing site, however what is not yet known is the impact that various exercise intensities and durations have on bone acquisition and growth during the different stages of puberty (3,11).

Impact on Strength & Power

Resistance training in children do result in increases in muscular strength (5-10). Similar to adolescents, much of the gain in muscular strength is due to neurological adaptations to resistance training (3,7-9,13). Increases in muscle size also aid in the development of muscular strength, but to a much lesser degree (7-9). Following a 12-week strength training program prepubescent and postpubescent children were able to improve there 10 rep max strength, motor capabilities, and flexibility compared to a non-exercised control group (13). Different kinds of training have been studied in children in order to determine which strength gains would carry over most into athletic performance. A power training regimen would consist of high velocity, explosive movements such as plyometrics, box jumps, and hurdle hops (6,8,9). Strength training focuses on slower velocity repetitions and greater external loading than power training (6,8,9). Behm et al. reviewed 107 studies to compare the effectiveness of both training modalities on sprint, strength, and jumping measures. Power training was found to impact measures of power, broad and vertical jump, better than strength training (6). However, in trained youth, Behm et al. found that strength training improved sprint measures more than power training and also generated greater lower limb strength (6). The previously untrained individuals differed from their trained counterparts in these findings, as power training impacted sprint measures more than strength training (6). The general consensus in this fields of research is not to choose between the two training modalities, but to instead incorporate both techniques to create a balanced training regimen (8,9). Overall, the literature regarding resistance training in children has been immensely positive (1-10,12-16). The potential benefits of resistance training closely coincide with the benefits exhibited in the adult population. Increases in muscular strength, power, endurance, and bone mineral density have all been noted (3-10,13,15).

What The Researchers Suggest

Guidelines for children engaging in resistance training should begin with proper supervision and need to be introduced to basic movement patterns (Push, Pull, Squat, Hinge, Jump, Sprint, Crawl). When developing a training program for a youth athlete it is important to focus on the training frequency, intensity, and volume of the workout as well as the order and selection of exercises. Faigenbaulm et al. suggest resistance training 2-3 days per week on non-consecutive days. These workouts should be performed at a low-moderate intensity (7,8). Prior to the strength training session, it is suggested that a 5-10 minute dynamic warm-up be performed at a moderate-high intensity(7,8). This will begin to excite the motor units of the muscles, increase core body temperature, and improve flexibility and range of motion (7,8). Training sessions should focus on balancing both upper and lower limb extremity exercises as well as incorporate movements that challenge the child’s core, balance, and proprioceptive skills (7,8). Whether the specific exercise is focused more on power or strength, 1-3 sets are recommended for both types (7,8). Repetition ranges for strength training should ideally be between 6-16, whereas power exercises are generally performed for no more than 6 repetitions in one set (7,8). Research suggests children are able to recover from exercise more quickly than adults are, therefore 1-2 minutes rest will most likely be sufficient for the child to adequately recover in between sets (7,8). At the end of the workout, a cool-down consisting of light calisthenics work as well as static stretching is recommended (8).

References:

1. Alves, AR. Concurrent training in prepubescent children: the effects of 8 weeks of strength and aerobic training on explosive strength and VO2MAX. Journal of Strength and Conditioning Research, vol. 30, no. 7, pp. 2019–2032, 2016

2. Alves, AR. Effects of order and sequence of resistance and endurance training on body fat in elementary school-aged girls. Biology of Sport, vol. 34, no. 4, pp. 379–384, 2017

3. Bass, S. Exercise before puberty may confer residual benefits in bone density in adulthood: studies in active prepubertal and retired female gymnasts. Journal of Bone and Mineral Research. Vol. 13, no. 3, 1998

4. Bradney, M. Moderate exercise during growth in prepubertal boys: changes in bone mass, size, volumetric density, and bone strength a controlled prospective study. Journal of Bone and Mineral Research. Vol. 13, no. 12, 1998

5. Behm, DG. Canadian society for exercise physiology position paper: resistance training in children and adolescents. Applied Physiology, Nutrition, and Metabolism, vol. 33, no. 3, 2008

6. Behm, DG. Effectiveness of traditional strength vs. power training on muscle strength, power and speed with youth: a systematic review and meta-analysis. Frontiers in Physiology 2017

7. Faigenbaum, AD. Youth resistance training: updated position statement paper from the national strength and conditioning association. The Journal of strength and conditioning research, vol. 23, 2009

8. Faigenbaum, AD. Pediatric resistance training: benefits, concerns, and program design considerations Current Sports Medicine Reports, vol. 9, no. 3, pp. 161–168, 2010

9. Faigenbaum, AD. Youth resistance training: the good, the bad, and the ugly-the year that was 2017. Pediatric Exercise Science, vol. 30, no. 1, pp. 19–24, 2018

10. Ferrete, C. Effect of strength and high-intensity training on jumping sprinting, and intermittent endurance performance in prepubertal soccer players. Journal of Strength and Conditioning Research, vol. 28, no. 2, pp. 413–422, 2014

11. Frisch, RE. Delayed menarche and amenorrhea of college athletes I relation to age of onset of training. Journal of American Medical Association 246;1559-1563. 1982

12. Gabler, M. The effects of concurrent strength and endurance training on physical fitness and athletic performance in youth: a systematic review and meta-analysis. Frontiers in Physiology, vol. 9, 2018

13. Lillegard, WA. Efficacy of strength training in prepubescent to early postpubescent males and females: Effects of gender and maturity. Pediatric Rehabilitation, 1:3, 147-157, 1997

14. Marta, CC. Differentiating maturational influence on training-induced strength and endurance adaptions in prepubescent children. American Journal of Human Biology, vol. 26, no. 4, pp. 469–475, 2014

15. Myers, AM. Resistance training for children and adolescents. Translational Pediatrics, vol. 6, no. 3, pp. 137–143, 2017

16. Tsolakis, CK. Strength adaptations and hormonal responses to resistance training and detraining in preadolescent males. Journal of strength and conditioning research, 18(3), 625-629, 2004