Children are always encouraged by their clinicians to do physical activity in order to have healthy bones. While low to moderate exercise is necessary in pre-adulthood for proper bone formation, it is unclear whether certain types of physical activity should be avoided as children in order to prevent bone damage. Despite the fact that mechanical stimulation is essential to maintain bone mass and bone density, weight training is often dismissed as an exercise option for children, due to the myth that weight training stunts growth. Yet, little research has been conducted to investigate weight training’s potential benefits in strengthening the matrix of children’s bones.
In the long bones of children, epiphyseal growth plates separate the epiphysis (terminal ends of long bones) and metaphysis (between epiphysis and diaphysis) of the bone. While it fuses with the rest of the bone in adulthood, the growth plate is an active structure in children primarily responsible for the longitudinal bone growth of long bones. This growth plate has three main components: Cartilaginous, fibrous, and metaphyseal. Each of these new components are the sites of new bone proliferation and deposition onto the outer surfaces of the foundational bone.
In order to understand why weight training might promote bone growth, it is necessary to consider the biomechanical properties of the epiphyseal growth plate in response to mechanical load bearing. Mechanical forces stimulate the synthesis of extracellular proteins which change the overall structure of the tissue. The plate’s geometry self-regulates based on the mechanical stimuli, and there is a specific adaptation that allows for compensation of the imposed demand. It is known that children have more elastic soft tissue in their bones, which has more potential for remodeling than in adults. Also, the growing skeleton seems to be more responsive than the mature skeleton to the effects of exercise. Therefore, when the growth plate in children is under a compressive, tensile, or shear load, it adapts to the imposed mechanical demands and changes its form.
Perhaps the myth stems from the fact that the epiphyseal growth plate in the long bones of an immature skeleton is the weakest structure of the bone. It is, therefore, a common site for injury. Moreover, the longitudinal bone growth tends to occur one year earlier than the peak gains in bone mineral content. This means that after a growth spurt, there is a period of relative bone weakness because the bone increases in length faster than it increases in width. This area is very prone to mechanical failure during that year. Another potential source of damage to the epiphyseal growth plate is over-activity. Excessive loading of the growth plate can suppress normal growth activity. Mechanical disruption of the growth plate can lead to physiologic failure, which could prevent normal bone growth from continuing. In other words, bone growth may be stunted.
While there are many opportunities for growth plate damage, avoiding exercise is not the solution. In fact, inactivity has negative influences on the growth plate as well. With an absence of exercise, the plate is not under any load. Since there is no imposed demand, the plate adapts by undergoing bone resorption. If bone resorption outweighs bone deposition, there will be a loss of bone mass.
Does this prove that the myth is true? Not quite. It seems as though high, static compressive loads lead to a reduction in the matrix synthesis of bones. It is unlikely, however, that a child would hold a heavy weight in one position for a long time. Research suggests that bones subject to low, intermittent compressive loads, such as performing several push-ups or bouncing a basketball repeatedly, can increase matrix synthesis.
Weight training only stunts growth when the epiphyseal growth plate is damaged by injury. The issue perhaps is not that weight training is a dangerous activity, but rather that children might lack the proper technique and coordination to practice it safely. Therefore, weight training practiced in children does not stunt growth provided there is proper instruction, supervision, and sufficient rest.
For more info, please check out:
Chandler, J., Eyers, C., & Mirtz, T. (2011). The Effects of Physical Activity on the Epiphyseal
Growth Plates: A Review of the Literature on Normal Physiology and Clinical
Implications. Journal of Clinical Medicine Research, 3(1): 1-7. Retrieved from
Khort, W., Bloomfield, S., Little, K., Nelson, M., Yingling, V., American
College of Sports Medicine, (2004). American College of Sports
Medicine Position Stand: physical activity and bone health. Med Sci
Sports Exerc 36,1985-1996
Edited by: Briana Fannin