In his seminal paper, Rowland clearly outlined the rationale, evidence, and implications for the biological control of physical activity. Ten years later, there has been some progress in this area related to childhood physical activity with perhaps the greatest progress being made in the areas of genetics and the neuroendocrinology of physical activity. It is clear that heredity contributes to the physical activity (and inactivity) phenotype and candidate genes are now being identified. Furthermore, animal models indicate that maternal exposure to various environmental factors may alter offspring physical activity. Although the mechanisms of this maternal-fetal interaction are unknown, it may involve the development programming of anatomical structures or biophysical pathways involved in energy homeostasis. In this regard, it is also clear that key brain structures and biomolecules involved in motivation, reward, and/or energy balance are also critical to understanding the biological basis of physical activity. Given the potential links between the neuro-endocrine and body composition changes during puberty and the decline in physical activity during this period, future multidisciplinary research in the human child and postnatal animal should be encouraged to provide a better understanding of the biological basis of physical activity during early life. Finally, there are also clear links between between the neuro-endocrine and body composition changes during puberty and the decline in physical activity with psycho-social factors. Thus, there should also be emphasis on understanding the "biocultural" development of the child and its influence on the physical activity phenotype.