Skeletal growth and effects of physical activity during adolescence

Sammanfattning: The aim of this thesis was to evaluate bone mass and bone size in girls and boys from age 12 to 16, with special attention to physical activity. We also wanted to retrospectively evaluate the effect of exercise for the years preceding age 12. The findings were as follows. Sixteen year old adolescents in a rural area had higher areal bone mineral density in the total body and the spine compared with 16 year old adolescents in an urban area. This implies a possibility to develop a higher peak bone mass and thereby presumably a lower risk of future fragility fractures. These findings could be the result of a higher physical activity in the rural group. Quantitative ultrasound measurements (QUS) in the calcaneus from age 11 to 16 show similar results as for adults, concerning the correlation with dual-energy X-ray absorptiometry (DXA) and single-energy X-ray absorptiometry (SXA) at other skeletal sites, and they also show a similar significant correlation with anthropometric data. QUS did not identify the same individuals with low bone mass as the X-ray techniques. Increased bone mass may be achieved in a population based cohort of boys (but not in girls) by moderate increased physical activity within the school curriculum from age 12 to 16. Before age 13, the skeleton seems to respond to moderate physical activity in weight loaded regions. Additional 3 years of high exercise level from age 13 to 16 do not contribute to an increased difference in bone mass when children with high and low activity level were compared in either gender. Skeletal growth from age 12 to 16 builds a bigger, but not a denser skeleton in the femoral neck. Growth in the appendicular skeleton precedes growth in the axial. Growth in size precedes accrual of bone mineral content (BMC). The girls were in all ages more maturely advanced in bone size and BMC than the boys.