Osteoporosis increases the risk of fracture due to decreased bone mass and deterioration of its structure which causes bone fragility. Low peak bone mass (PBM) at the end of adolescence or at the early stage of adulthood is a risk factor of osteoporosis. Bone development during growth is crucial for bone health throughout the whole life. Although the variation in bone outcomes is determined by heredity, lifestyle-related factors including physical activity (PA) and dietary habits can explain up to approximately 30% of the variation in PBM. It is known that sufficient moderate-to-vigorous PA levels and sufficient nutritional intakes, such as calcium, protein and vitamin D are needed to promote bone development. However, only a few studies focused on the combined and interactive effects between the dietary intakes and PA on bone health during growth. In addition, body mass is an important predictor of bone mineral content, according to previous studies, lean mass has a positive association with bone development, while the role of fat mass to bone is still controversial. Previous paediatric studies indicate the partial influence of endocrine markers on bone growth and especially during puberty, but the mediating role of endocrine markers on the relationship between body composition and PA with bone growth requires further research. Therefore, the overall objective of this research project is to assess the combined role of physical activity and dietary factors with bone development and examine the role of endocrine markers and body composition from childhood to early adulthood.