The Sport Information Resource Centre
The Sport Information Resource Centre
Rows of dumbbells in the gym with sunlight in morning.

Once considered a fringe activity, weight training has grown in popularity in the last 20 years due to its benefits for improving health, physical fitness, and performance.  Weight training is often included in high school physical education classes and promoted for young athletes as a supplement to sport training.  However, various myths regarding weight training for children, including the risk of damaging growth plates resulting in stunted growth, leave parents and coaches with safety concerns. While a review of the research on weight training in children concluded that lifting weights has no detrimental effect on skeletal growth (Malina, 2006), many questions remain. This article provides insight on the appropriateness and effectiveness of weight training for children and youth to ensure coaches, parents and athletes are making informed decisions.

What is Weight Training?

Weight training is exercise performed using additional loads, such as barbells, dumbbells, or from various types of machines.  Physical fitness programs often incorporate a combination of both loaded and unloaded exercises.  However, unloaded exercises – which include running, jumping, and agility tasks – should not be confused with weight training as they have different effects on the body.  The primary benefit of weight training is increased muscle strength.  Additional benefits from weight training may include improved flexibility and bone health.  Combined, these adaptations improve the capacity and safety to perform physical activity.

The Physics of Weight Training

One reason why weight training is generally safe is that the forces placed on the body are often less than in commonly performed during physical education and sport tasks. Consider the forces regularly imposed on the body. When standing upright, the gravitational force acting on the body is equal to bodyweight.  During an exercise such as a squat or deadlift, the force increases by the amount of additional weight lifted.  For example, if squats were performed with a 45 lb barbell, the force acting on the body would be bodyweight plus 45 lbs.  In contrast, when performing a vertical jump, the force on the body when landing is more than three times bodyweight.

Another example is the comparison between a push up and a bench press.  Push ups are commonly included in physical education classes and physical fitness tests, including the now superseded Canada Fitness Award Program.  The average weight for a 12-year girl is approximately 92 lbs.  During a push up, the forces acting on the arms are about 70% of bodyweight, so for the 12-year old girl approximately 64 lbs.  However, many children (and adults) struggle to perform push ups. Replacing push-ups with a bench press or chest press, the forces acting on the arms could be reduced significantly. For example, an unloaded barbell weighs 45 lbs. Moreover, the forces can be gradually increased by adding small weights in proportion to the individual’s abilities.

Weight Training Adaptations

Weight training can increase muscle strength, bone density, and may have benefits for motor skill performance (Behm, Faigenbaum, Falk, & Klentrou, 2008).  Muscle strength can increase due to: 1) neurological adaptations – changing how muscles are activated, or 2) hypertrophy – increasing muscle size.  Neurological adaptations are reversible, meaning that strength gains are lost after training is stopped. Strength adaptations from hypertrophy are more persistent as it takes much longer to lose muscle size.  In pre-pubertal children muscle strength increases primarily due to neurological adaptations, whereas post-pubertal children and adults will experience both neurological adaptations and hypertrophy.

As bone formation and growth is a normal process in children, weight training has the potential to amplify bone development, including increasing bone mineral density.  These adaptations are important for long-term health.  However, bone adaptations may only occur for certain exercises, such as those performed standing, as opposed to those performed sitting or lying down.

Increased muscle strength from weight training may allow motor skills, such as running, jumping, and throwing, to be performed better.  However, the effectiveness of weight training to enhance motor skill performance depends on the child’s motor skill ability and age.  In younger children, those who have poor or deficient motor skills benefit most from weight training as their muscle strength may be sub-optimal and limiting their ability to perform motor skills.  Younger children who have typical or above average motor skill abilities are not likely to benefit.  In contrast, weight training can have substantial effects on motor skill performance in older children (over 14-15 years) due to the capacity to increase muscle strength through hypertrophy.

Should Children Perform Weight Training?

Given that weight training is safe, has positive effects on muscle strength and bone health, and may positively impact performance of motor skills, it has been recommended that children participate in weight training programs (Zwolski, Quatman-Yates, & Paterno, 2017).  However, this recommendation needs to be viewed from the perspective of normal growth and development, including acquisition and refinement of fundamental motor skills.

For children and youth prior to puberty, the focus for physical activity should be on the acquisition of motor skills. Motor skills include basic skills (e.g. crawling, walking, and object manipulation, typically acquired between 0 and 4 years), fundamental movement skills (e.g. running, hopping, skipping, jumping, throwing, and kicking), and sport specific movement skills. Unlike basic motor skills, fundamental and activity specific motor skills are not inherently learned – they require targeted instruction and practice (Chiodera et al., 2018; Jones et al., 2011; Logan, Robinson, Wilson, & Lucas, 2011).

Three smiling kids with an assortment of sports equipmentAs children develop their fundamental and activity specific motor skills through practice, their strength will also increase  (Haga, 2009).  For example, in running and jumping, the lower extremity muscles would get stronger, whereas in climbing tasks, the upper extremity muscles would be trained.  Therefore, a multisport approach not only enhances fundamental and activity specific motor skills, it also contributes to physical fitness throughout the body.

The optimal ages to acquire and refine fundamental motor skills are believed to be between 4 and 10 years, prior to puberty.  Further refinement may be required during puberty as the child’s body grows to new proportions.  Considering the importance of practice to acquire and refine fundamental movement skills, a large proportion of physical activity time should be dedicated towards instruction and practice of a large variety of motor skills.  Consequently, weight training is not an ideal activity in this age range as it would limit the variety of activities a child could pursue.

Weight training is most effective in children following puberty.  Muscle strength and motor skill performance increase throughout puberty; however, they begin to plateau between 14 and 16 years in girls and 16 and 18 years in boys.  Further increases in motor skill performance post-puberty require increases in muscle size and strength.  Considering the earlier plateau in muscle strength and motor skill performances in girls, girls may benefit from starting weight training at an earlier age than boys.

Special Circumstances

Weight training may be important in younger children in certain situations.  For example, weight training appears to be beneficial in children with cerebral palsy who have below average strength.  Similarly, children who have delayed motor and/or physical development, which may be due in part to poor muscle strength, may improve function with weight training.  Weight training has also been incorporated in exercise programs for children with adolescent idiopathic scoliosis.  In each of these scenarios, the training programs are designed to specifically target deficits – i.e. individual muscle weaknesses – rather than to improve general physical fitness.

The Bottom Line

Up to approximately 14 years in girls and 16 years in boys, physical activity programming should emphasize targeted instruction and practice to acquire and refine fundamental and activity specific motor skills.  A variety of motor skills should be performed, and their difficulty should be progressed to allow complementary physical fitness development.  This approach is consistent with current trends in the sport and physical activity sector promoting the value of developing children’s fundamental movements skills through multi-sport experiences supporting life-long physical activity.  After puberty, approximately 14 to 16 years in girls and 16 to 18 years in boys, weight training can be incorporated into athletic training programs or active living practices. Weight training, including use of heavy loads within the child’s capabilities, is safe, however, this assumes proper exercise technique and supervision by a qualified and experienced coach or trainer.


About the Author(s)

Loren Chiu is an Associate Professor at the University of Alberta. His research studies musculoskeletal function and its influence on human movement mechanics. Moreover, he provides support to enhance performance in youth and university athletes, and to restore function in individuals with musculoskeletal injury.

References

Behm, D. G., Faigenbaum, A. D., Falk, B., & Klentrou, P. (2008). Canadian Society for Exercise Physiology position paper: resistance training in children and adolescents. Applied Physiology, Nutrition, and Metabolism, 33, 547-561.

Chiodera, P., Volta, E., Gobbi, G., Milioli, M. A., Mirandola, P., Bonetti, A., . . . Vitale, M. (2018). Specifically designed physical exercise programs improve children’s motor abilities. Scandinavian Journal of Medicine & Science in Sports, 18, 179-187.

Haga, M. (2009). Physical fitness in children with high motor competence is different from that in children with low motor competence. Physical Therapy, 89(10), 1089-1097.

Jones, R. A., Riethmuller, A., Hesketh, K., Trezise, J., Batterham, M., & Okely, A. D. (2011). Promoting fundamental movement skill development and physical activity in early childhood settings: A cluster randomized controlled trial. Pediatric Exercise Science, 23, 600-615.

Logan, S. W., Robinson, L. E., Wilson, A. E., & Lucas, W. A. (2011). Getting the fundamentals of movement: a meta-analysis of the effectiveness of motor skill interventions in children. Child: Care, Health and Development, 38(3), 305-315.

Malina, R. M. (2006). Weight training in youth-growth, maturation, and safety: an evidence-based review. Clinical Journal of Sports Medicine, 16(6), 478-487.

Zwolski, C., Quatman-Yates, C., & Paterno, M. V. (2017). Resistance training in youth: laying the foundation for injury prevention and physical literacy. Sports Health, 9(5), 436-443.


The information presented in SIRC blogs and SIRCuit articles is accurate and reliable as of the date of publication. Developments that occur after the date of publication may impact the current accuracy of the information presented in a previously published blog or article.