2 Ways Bone Modeling Occurs throughout Life: Hypertrophy and Atrophy - dummies

2 Ways Bone Modeling Occurs throughout Life: Hypertrophy and Atrophy

By Steve Glass, Brian Hatzel, Rick Albrecht

Bone modeling occurs throughout life in two ways: hypertrophy (growth) or atrophy (shrinking). Understanding the difference between the two enables you to acknowledge the effects that being physically active has on your support system and general health as you age.

Bone development in the early years

During the early years, as children walk, run, and otherwise function in their daily activities, bones are continually ossifying (hardening and becoming more dense) and meeting the demands of the structural system. Bone hypertrophy occurs in response to this activity during these years.

Despite the ossification that is occurring, adolescents still possess points of vulnerability within these structures.

  • Problems with the growth plate: The epiphyseal (or growth) plates are especially vulnerable to overuse. Significant compression and shearing of the epiphyseal plate can slow bone growth and have a long-lasting impact on the overall development of the bone. Shearing typically occurs when muscles exert force on the bone during activity, whereas compression is usually a result of walking, running, and jumping.

    In moderation, these activities are normal and healthy; in fact, they’re necessary for normal bone development. But when they progress too quickly or are engaged in to the extreme, negative effects can occur.

  • Osgood-Schlatter disease and other difficulties with the apophysis: In adolescents, bone injury often revolves around the disproportionate, or imbalanced, abilities of the muscular system compared to the skeletal system. Through adolescence, significant growth and development occur within the muscular system, and additional hormonal influences further spur muscular development such that the muscles begin to make demands that the bones aren’t quite ready to accommodate.

    As muscles pull harder and harder on the bones, the modeling occurs so quickly that apophysitis (the inflammation of the apophysis, the raised section where tendons and/or muscles insert onto the bone) occurs, which can be quite painful.

    The most common site of apophysitis is where the patellar tendon inserts on the tibial tuberosity. The increased tension that both bone and muscle growth place on this site can cause tenderness where the tendon attaches. This condition is commonly referred to as Osgood-Schlatter disease. In other cases, the increased tension created by muscles causes the growth plates to shift, resulting in growth retardation.

Many issues like apophysitis are complicated by over activity in adolescents. The solution, however, isn’t to avoid activity; in fact, encouraging regular physical activity is paramount. The key is to recognize signs of overuse and make certain that children progress into activity in a way that allows for their bodies to accommodate the stresses they’ll incur.

Inevitably, many adolescents will experience complications due to growth and activity. In nearly all cases, the discomfort goes away over time as the body is able to better accommodate the forces, and the bones adapt appropriately.

Changes in bones throughout the adult years

By adulthood, the bones have become fully ossified, or hardened, and the risk of injury to the growth plates due to overuse is no longer an issue. However, even though longitudinal growth does not occur in the adult years, circumferential growth continues for quite some time and is usually dictated by function.

That’s why it’s so important to exercise regularly and to be active. The more active you are, the more dense your bones become. Because bones are constantly accommodating their environment, they change — either growing stronger or weaker — to meet the demands that the forces put on them.