Even children and adolescents not involved in elite organized sport tend to have higher bone density in their dominant arms as compared to their non-dominant arms. Since genetic, nutritional, and endocrine factors are shared by both arms, differences in bone mineralization in these unilateral control studies strongly suggest that preferential strain placed on the limb by specific physical activities causes modeling (9).

The fact that bone responds best to physical activity with high load intensities in unusual patterns is different from the cardiovascular response to physical activity in which aerobic capacity is improved through long duration and relatively low intensity. This recognition has implications when selecting methods for examining physical activity’s effect on bone and when considering exercise prescription or community-level health promotion recommendations for children and adolescents. Specific activities that appear important to bone health such as weight lifting are of less importance to cardiovascular health.

8. Kannus P, Haapaslo H, Sankelo M, Sievanen H, Pasanen M, Heinonen A et al. Effect of starting age of physical activity on bone mass in the dominant arm of tennis and squash players. Ann Intern Med 1995;123:27-31.