FIG. 4.

Relationships between physical activity, skeletal development, and body composition. We propose that physical activity exerts a direct positive effect on both periosteal bone growth (reflected by height-adjusted bone area) and volumetric BMD (reflected by aBMC). Moreover, physical activity indirectly stimulates periosteal bone growth as a consequence of effects on lean mass. In contrast, the tendency of physical activity to decrease fat mass acts to reduce periosteal bone growth.