The idea of weight training for children (preadolescent and adolescent) has always raised questions. The concern most often raised is whether or not weight training puts children at an increased risk for injury. A secondary question that is raised is whether children would benefit from weight training, if they are not physiologically mature (e.g., low androgen levels). This chapter will review these issues and offer guidance to the proper (safe) training techniques and programs, followed by a review of the expected training responses and outcomes as characterized in the research literature.
Often the risk of the epiphyseal growth plate injuries is mentioned; however, to date there have only been a few published papers that document such injuries and often these injuries are owing to lack of adequate education (training) and supervision of the children. Often injuries are owing to improper lifting techniques or the participant's workloads are progressed to quickly. However, injuries may increase for the child athlete, who has inadequate strength for his or her chosen sport and in these cases weight training offers protection from potential injuries.
Children have been shown to increase their strength from participating in weight training programs. Two separate meta-analytic reviews1,2 showed that children increased their strength with resistance training by 13% to 30%. These analyses also determined that there was a greater effect size seen in isotonic training, followed by isometric exercise and finally by isokinetic training. However, the reviews could not determine the optimal training program because the studies were limited by gender (mostly males), age range, differences in intensity, duration, and frequency. It is well documented that the strength (force) of a muscle is directly related to its cross-sectional area. Increase in muscle size is related to the androgen hormone. Because prepubertal children lack adequate androgen hormone, the strength gains at this age are largely believed to be because of neuronal adaptations. Various aspects of muscle strength testing, strength training, growth and maturation, metabolism, and muscle fiber types have been the subject of extensive body of published literature.1–20
When muscles respond in the manner for which they are activated, a specific motion either lengthening or shortening or no movement occurs. A concentric muscle action refers to a shortening of the muscle fibers accompanied by movement of the respective joint. The muscle is shortening because the actions of the muscle fibers are greater than the external resistance and the muscle shortens (Figure 5-1). Since the internal muscular forces are greater than the external resistance, it has also been described as performing “positive” work.
Lifting a weight during biceps curl is an example of concentric muscle action in which the muscle shortens while performing positive work.