Influence of rapid growth on skeletal adaptation to exercise.

During rapid growth, increased body weight and muscle strength result in increased loads on bone. Bone adapts to these increased strains by increasing bone modeling and remodeling. As the growth rate decreases, bone that was formed as a result of these adaptations continues to mineralize and "catch up", and bone modeling and remodeling decreases. Bone benefits of exercise in childhood are reported in some studies, although we observed less BMC gain at trabecular-rich sites during the peri-pubertal period in children who jumped than those who did not. Data from 13 existing pediatric exercise studies were compiled to determine whether similar patterns of age-related bone changes could be identified, and whether the bone benefit of exercise differed depending upon pubertal stage. The benefit of exercise on total body BMC gains occurred across all ages, whereas greater exercise-induced gains at the spine and hip were observed in younger children compared to older children. The majority of studies found a positive effect of exercise on bone, but typically this involved limiting the analysis to specific sub-populations (i.e., higher calcium intake, lower baseline activity levels, smaller body size). Limitations of the studies published to date are discussed.