Study of the Metabolic Profile of Bone in Professional Athletes as a Function of the Kind of Physical Activity Performed

Genetics explain about 70% of the inter-individual variance of bone mineral density (BMD) but maintenance and acquisition of bone mass strikingly depend on environmental factors as diet, calcium intake (in both quantitative and qualitative terms), and physical activity (PA). Among these, the biomechanical load generated by different kinds of PA represents the most important physiological stimulus able to increase bone mass and density.

Bone is a metabolically active tissue that undergoes to continuous remodeling throughout the coupling of resorption (operated by osteoclasts) and formation (operated by osteoblasts). Osteocytes, the quiescent form of osteoblasts, regulate the activity of the other two cell types and directly respond to load. Under normal conditions, resorption and formation are strikingly coupled and this guarantees an equilibrium between old bone matrix removal and new matrix deposition. This equilibrium is dependent upon several hormones and local mediators (e.g., cytokines, myokines, adipokines). Physiological (e.g., growth, aging, PA) and pathological conditions (e.g., metabolic diseases, bed rest, drugs) inbalance this equilibrium towards one side and, hence, affect bone mass. Regarding PA, for example, it is known that weight-bearing aerobic activity has positive effects on BMD and, hence, it is considered a preventive strategy against post-menopausal bone loss.

Differently from radiological imaging, that gives information about established architectural changes happened at a specific site in bone, biochemical and molecular markers of bone turnover give an instantaneous picture of the metabolic status of bone cells and, possibly, their immediate response to a stimulus.

Other than the bony response, PA activates several endocrine responses and particularly, the whole set of responses needed for managing the energy stores and to save the most nobile functions (e.g., brain, hearth). Hence, bone is subjected to the endocrine regulation of energy usage but, as recently discovered, being it the primary mechanosensor of load, it acts itself as an endocrine organ able to signal to other tissues and organs the changing environmental conditions.

Although several molecular aspects about the effects of PA on bone metabolism and the bone-energy cross-talk, a number of unresolved questions still exists. The study of different physiological models (i.e., athletes belonging to different disciplines) might allow the identification of common mechanisms regulating the response to PA and, from another side, to understand the physiological response to different stresses applied onto the muscle-skeletal apparatus.