Question: 

Bone mass can be considered as the net product of counteracting metabolic processes: bone formation and resorption. Blood molecules are identified as bone metabolic activity markers: short exercise is insufficient to modify their concentrations, while strenuous physical activity could modulate bone metabolism. The aim of this work was to evaluate bone metabolism in professional cyclists during a three weeks-long stage race.

Methodology: 

We studied 9 professional cyclists engaged in 2011 Giro d'Italia stage race. Pre-analytical and analytical phases strictly followed academic recommendations. Blood drawings were performed at days -1, 12 and 22. Plasma and serum samples were stored at –80°C until assayed by ELISA. Serum activities of bone alkaline phosphatase (BAP) and tartrate-resistant acid phosphatase 5b (TRAP5b), and the concentration of total osteocalcin (OC) were evaluated. Furthermore, plasma parathyroid hormone (PTH) concentration was assayed. Statistical analysis were performed.

Results: 

Despite BAP activity levels did not change during the race, OC significantly decreased along the time. On the contrary, TRAP5b levels increased between day-1 and day 22. Moreover, no variations were observed in PTH levels.

Conclusions: 

The reduction of OC concentration and the increase of TRAP5b activity are indicative of bone resorption throughout the race. Cycling is a not weigh bearing sport, but, being a strenuous activity, it affects bone metabolism. Moreover, stable PTH concentrations could confirm the hypothesis that changes in bone metabolism are not dependent on variations in haematic calcium and phosphate. On the contrary, they are directly related to strenuous physical activity in load absence.