Exercise, Hormones, and Skeletal Adaptations During Childhood and Adolescence

Abstract

Although primarily considered a disorder of the elderly, emerging evidence suggests the antecedents of osteoporosis are established during childhood and adolescence. A complex interplay of genetic, environmental, hormonal and behavioral factors determines skeletal development, and a greater effort is needed to identify the most critical factors that establish peak bone strength. Indeed, knowledge of modifiable factors that determine skeletal development may permit optimization of skeletal health during growth and could potentially offset reductions in bone strength with aging. The peripubertal years represent a unique period when the skeleton is particularly responsive to loading exercises, and there is now overwhelming evidence that exercise can optimize skeletal development. While this is not controversial, the most effective exercise prescription and how much investment in this prescription is needed to significantly impact bone health continues to be debated. Despite considerable progress, these issues are not easy to address, and important questions remain unresolved. This review focuses on the key determinants of skeletal development, whether exercise during childhood and adolescence should be advocated as a safe and effective strategy for optimizing peak bone strength, and whether investment in exercise early in life protects against the development of osteoporosis and fractures later in life.

Sex-Specific Muscular Mediation of the Relationship Between Physical Activity and Cortical Bone in Young Adults

“…These mediators begin to highlight the potential combined contribution of the mechanical and the hormonal muscular environment, which may be key to understanding sex-specific adaptation to PA. (19,20) For example, traditional discourse has highlighted muscle's role to be the structure that applies mechanical forces to bone, primarily during dynamic loading, but also to maintain postural stability. (18,44) Though our serial mediation model begins to address these potential mechanisms, we did not measure hormones or specific loading rates so are only able to speculate on the relative importance of mechanical versus biochemical mechanisms by which muscular factors may mediate the relationship between PA and bone status, an important area for future research. The degree to which bone formation occurs as a result of dynamic loading is directly related to the customary strain stimulus (ie, load characteristics such as peak strain, loading frequency, and number of loading cycles).…”

“…Furthermore, global and localized hormonal environments may also play a key role in modulating sex-specific mechanosensitivity through factors such as the concentration of estrogen receptor-α, which is dependent on estrogen concentrations, (42,43) or concentrations of anabolic hormones such as growth hormone (GH) and insulin-like growth factor-1 (IGF-1). (18,44) Though our serial mediation model begins to address these potential mechanisms, we did not measure hormones or specific loading rates so are only able to speculate on the relative importance of mechanical versus biochemical mechanisms by which muscular factors may mediate the relationship between PA and bone status, an important area for future research.…”

“…(17) Sex-specific hormonal environments drive bone accrual at different rates in girls and boys during childhood and adolescence, leading to differences in both bone mass and structure in adulthood. (18) For example, women tend to have a larger bone area than men for a given muscle size, specifically at habitually loaded sites. (19,20) Women may also have a lower relative muscle force (force output per unit of cross-sectional area) than their male counterparts, (14) suggesting a difference in the mechanical relationship between muscle and bone status.…”

Bone Mass and Strength in School-Age Children Exhibit Sexual Dimorphism Related to Differences in Lean Mass: The Generation R Study

“…Previous research suggests that the skeleton is most sensitive to mechanical loading during childhood and adolescence . The mechanical stimuli applied to bone are induced by muscle contractions that move the body in opposition to gravitational forces.…”

“…(10) Previous research suggests that the skeleton is most sensitive to mechanical loading during childhood and adolescence. (11,12) The mechanical stimuli applied to bone are induced by muscle contractions that move the body in opposition to gravitational forces. Yet, the relative contribution of each of these sources (including ground, substrate, and joint reaction forces) to the adaptive response of bone remains controversial given their interdependence.…”