Adaptive skeletal responses to mechanical loading during adolescence

Adolescence, defined as the period between puberty and maturity, provides a window of opportunity for positive skeletal adaptations to mechanical loading unlike any other period in life. Age-related bone loss highlights the importance of accumulating sufficient bone mass during formative years. Adolescents who regularly engage in weight-bearing mechanical loading appear advantaged in site-specific markers of bone mass. The positive influence of physical activity on bone mineral accrual during growth has been extensively studied; however, few studies have examined skeletal responses to mechanical loading during adolescence. Weight-bearing physical activity, particularly high-impact sports such as gymnastics, is recognised as being more osteogenic than weight-supported activities. Unilateral loading activities such as tennis or squash provide a direct comparison of skeletal response without sampling bias or genetic confounding. Intervention and longitudinal studies show evidence of positive skeletal adaptations; however, sustainability of skeletal advantages remains unclear. Limitations inherent with single-plane dual x-ray absorptiometry technology are well recognised. The integration of densitometric data with structural responses to mechanical loading using 3-dimensional imaging technologies such as peripheral quantitative computed tomography and magnetic resonance imaging appears vital to enhancing our understanding of adolescent musculoskeletal health. The framework of the human skeleton provides protection of internal organs, support against gravity, a lever system enabling movement and a reserve of ions for the maintenance of serum homeostasis. Active adolescents require a skeletal system with a composition (material properties) and organisation (structural properties) to accommodate functional demands of intense physical activity within a lightweight design facilitating energy-saving locomotion.[1] Peak bone mass reflects the maximal lifetime amount of bone mineral accrued in individual bones and the whole skeleton.[2] Peak bone mass value is a consequence of net accrual of bone during childhood and the balance between accrual and resorption in adulthood.[3] Theoretically, because bone loss occurs with aging, people who acquire maximal bone mass in their early years should be at a reduced risk of skeletal fragility and fracture in later life. Agreement on the age at which peak bone mass is achieved remains illusive and site specific.[2,4, 5, 6, 7, 8] Genetics determine the basic morphology of the skeleton, but final bone mass and architecture are modulated by adaptive mechanisms sensitive to mechanical loading.[9] Pioneer research in loading conducted by Wolff (1882) was the first to document changes in bone mass that accompany different mechanical loadings. Internal architecture and external structure alter as a consequence of primary stimuli from mechanical loading