Based on her previous research on pediatric bone health, Dr. Kerry MacKelvie believes that perhaps the greatest hope for preventing osteoporosis in later life is to intervene during childhood. Kerry has studied how high impact exercise affects bone mass and structural changes during growth, and she has investigated the effects of ethnic background on bone health. Now Kerry is bringing together in one study an investigation of all the factors that may contribute to bone strength during childhood: exercise, hormones, body mass and composition, and ethnicity. She will study Asian and Caucasian boys who have not yet reached puberty, focusing on bone mass changes over time for both overweight boys and inactive boys. The study is particularly relevant to Vancouver's population, as it will examine and compare ethnic-specific hormonal, body composition and bone mass changes during growth in both Asian and Caucasian children.