Age, maturity, and plyometric training

I do not deal with a lot of children in my business, however, the book Essentials of Strength Training and Conditioning offers great insight into the physical development of children (Baechle & Earle, 2008 pp. 142-150, 422). Without getting into specifics or the tests involved, it is known that all children do not grow or mature at the same rate however, the degree of physical maturity is related to fitness strengths. Although there is no evidence that physical training interferes with growth, as a child matures into adolescents the training programs may need to be individually modified.
Peak height velocity refers to growth spurts. It is during this time of rapid growth that young athletes are most susceptible to injury. Weakness in bones due to flexible and growing epiphyseal plates, muscle imbalances around the joints, and tight muscle-tendon units involved with fast growing bones are prevalent risk factors. Some researchers believe that the epiphyseal plates of younger children are stronger than those of adolescents.
One of the goals of plyometric training is to not only enhance the muscular system but to also improve the nervous system (Brown, 2001). Until sexual maturity is reached, the nervous system of a child is not at the same skill level as an adult. Myelination of the nerve fibers is not yet complete, therefore reaction times will be slower and coordinated movements may appear difficult. As the nervous system matures speed, balance, agility, and power improve (Baechle & Earle, 2008).
With all of this said, research indicates that resistance exercise does improve physical ability and sports performance and is encouraged as long as specific guidelines are followed. The guidelines are similar to those that adults should also adhere (Baechle & Earle, 2008):

• Dynamic warm up
• Static stretching after resistance training
• Begin with light loads and increase gradually
• Advanced multi-joint exercises can be performed using appropriate loads
• with proper form

For plyos specifically (Baechle & Earle, 2008):

• High intensity lower body drills such as depth jumps are contraindicated
• due to the open epiphyseal plates.
• Exercises should be used to improve neuromuscular coordination and anaerobic
• skills used in sports
• The quality of the movements form should be emphasized
• There should be a gradual progression from simple to complex movements
• Minimum of 2-3 days between workouts

Baechle, T. & Earle, R. (2008) Essentials of strength training and conditioning. Champaign, IL. Human Kinetics

Brown, L. (2001) Plyos or not. National Strength & Conditioning Association
Volume 23, Number 2, pages 70–72