The concern that high-intensity training, such as powerful jumping and bounding exercises, might negatively affect a child’s growth is common among parents and coaches. This worry often stems from a misunderstanding of the forces involved and the specific biology of the developing skeleton. It is a common misperception that structured explosive movements will prematurely close or damage the physical structures responsible for lengthening bones. Understanding the mechanics of these activities and the science of skeletal development provides a clear answer.
What Plyometrics Are and How They Work
Plyometrics are a specific type of training designed to improve power and reactive strength by harnessing the body’s natural elasticity. This training relies on the stretch-shortening cycle (SSC), which involves three distinct phases of muscle action. The cycle begins with a rapid eccentric phase (muscle lengthening under tension), followed by a very short amortization phase (the transition period). It concludes with an explosive concentric phase, where the muscle shortens to produce a powerful movement, such as a jump.
Examples include box jumps for vertical power and hopping and bounding for horizontal movement. The goal is to minimize the time spent in the amortization phase to maximize the release of stored elastic energy from the tendons and muscles. Plyometric training improves the neuromuscular system’s ability to react quickly and forcefully.
How Skeletal Growth Occurs in Youth
Skeletal growth in children and adolescents occurs primarily through endochondral ossification, which takes place in specialized areas known as epiphyseal plates, or growth plates. These plates are temporary layers of cartilage located near the ends of the long bones, such as the femur and tibia.
The growth plate is organized into distinct zones. In the proliferative zone, cartilage cells rapidly divide, pushing the ends of the bone further apart and providing the foundation for lengthening. These cells are eventually replaced by new, solid bone tissue, a process that continually adds length to the bone.
Because the growth plate is composed of cartilage, it is structurally weaker and more vulnerable to excessive shear and compressive forces than the surrounding mature bone. Longitudinal growth ceases only after the entire plate has been replaced by bone, a process known as skeletal fusion, which typically occurs at the end of puberty.
Research Findings on Plyometrics and Growth Plates
Research from pediatrics and sports medicine indicates that properly designed and supervised plyometric training does not pose an increased risk to the growth plates of young athletes. The concern that these exercises will cause premature fusion or damage the plates is unfounded when training protocols are appropriate for the child’s developmental stage. Studies show that forces experienced during supervised, low-to-moderate intensity plyometric drills are often no greater than those encountered in common, unstructured youth activities.
Unstructured play and landing in competitive sports frequently involve impact forces that exceed those generated during controlled plyometric exercises. The primary risk to the growth plate comes from improper technique, training while overly fatigued, or a sudden, excessive increase in volume or intensity. When technique is poor, the bones and joints absorb impact unevenly, leading to shear forces that may cause injury.
When implemented correctly, plyometric training is considered a safe and effective method for improving neuromuscular control and power in youth, potentially contributing to better bone density.
Key Principles for Safe Youth Plyometric Training
Implementing plyometric exercises safely requires adherence to specific guidelines focused on technique and progressive overload. A foundational prerequisite is the mastery of fundamental landing and decelerating mechanics. Athletes must first demonstrate baseline strength and the ability to absorb force properly before progressing to explosive movements.
Training must begin with low-intensity drills, such as continuous hopping, skipping, or low-box jumps, allowing the neuromuscular system to adapt gradually. High-intensity exercises like depth jumps should be reserved for older, skeletally mature adolescents who have built a solid strength base.
Qualified supervision is important to ensure correct form and limit the total volume of jumps. For younger athletes, this might mean starting with a maximum of 50 to 60 foot contacts per session. Adequate recovery time (48 to 72 hours between intense sessions) must be provided to prevent fatigue-related injuries.