Some early scientific studies indicated that strength training was not effective for children prior to puberty. However, more recent experiments clearly indicate that strength training programs can help increase strength in boys and girls, regardless of age.

Strength Training, Body Size and Composition

Few scientific studies are availalbe on the effects of strength training on body size and composition in boys and girls. The strength training programs have generally resulted in small changes in body weight and fatness and have had no influence on height.

It appears that short term (e.g., 20 weeks) strength training programs have very little influence on body size and composition during early childhood, especially before adolescence. Whether long team training will more significantly impact body size and composition remains to be determined.

Only a few studies have investigated the issue of strength training and muscle hypertrophy (increase in muscle size). Such training prior to and during early puberty does not appear to cause muscle hypertrophy in boys or girls.

By contrast, several studies have indicated that such training during adolescence produces significant increase in both arm and leg girths in boys implying a muscle hypertrophy effect of training. There is no information on the effects of strength training of muscle hypertrophy in adolescent girls.

Strength Training and Performance

Many of the sports in which children participate demand considerable strength and power, and perfromance in these sports might be improved with strength training. From a logical perspective, performance could be improved through either the strength gains, changes in body size and composition, or the preventative and rehabilitative outcomes of strength training.

Unfortunately, there is no scientific proof that strength training directly causes improvements in sports performance during childhood. There is some evidence, however, that strength training may contribute to enhanced performance by reducing injury rates for contact sports and by reducing recovery time from injury.

Strength Training and Safety

Much of the concern for safety in strength training involves the potential damage to either the growth plates of long bones or toe joints and soft tissues. Such damage could cause stunted growth, acute or chronic pain, impaired motor function, and perhaps disfiguration. However, research suggest that well supervised strength training programs can minimize the risk of injury to growth plates, joints, and soft tissue.

Strength Training Guidelines for Children and Adolescents

• Undergo physical and medical check-ups before training.
• Use strength training as only one of a varietty of sport and fitness activities.
• Use calisthenics to initially build muscle endurance and strength.
• Use a variety of training methods: calisthenics, free weights, machines.
• Always develop proper technique first, with low resistance.
• Progress from low resistance and high repetitions to higher resistance and fewer repetitions.
• Exercise muscles through their full range of motion.
• Restrict strength training exercise to three times a week.
• Use a circuit system approach to maximize cardiovascular fitness.
• Avoid emphasis on negative or eccentric exercises (e.g., lowering heavy weights).
• Include warm-up before training and flexibility exercises after training.
• Provide constant and experienced adult supervision.
• Heed pain as a warning, and seek medical advice.

Suggested reading on this subject:

Blimke, CJR, Resistance Training During Preadolescene. Issues and Controversies, Sports Medicine 15 (6): 389-407, 1993.

Blimke, CJR, Benefits and Risks of Resistance Training in Children. In: Intensive Participation in Children's Sports. BR Cahill and AJ Pearl (eds.), American Orthopedic Society for Sports Medicine. Human Kinetics, Champaign, IL, pp. 133-165, 1993.