Effect of physical fitness and endurance exercise on indirect biomarkers of recombinant growth hormone misuse: insulin-like growth factor I and procollagen type III peptide.

Serum insulin-like growth factor-I (IGF-I) and procollagen type III peptide (P-III-P) have been proposed as indirect biomarkers of rhGH misuse in sports. The purpose of the present study was to investigate concentrations of these biomarkers in athletes at different levels of physical fitness and endurance exercise. Serum total IGF-I and P-III-P were measured in 96 elite athletes of various sports along the training season; in 21 recreational athletes at baseline non-exercising conditions and in another 129 recreational athletes before and after long-distance races (10 and 21 km). No differences were evidenced for IGF-I concentrations, but statistically higher values of serum P-III-P were found in elite athletes compared to recreational ones. Among elite athletes, the specific sport did not affect serum IGF-I. However, P-III-P was statistically higher in the sport performed by the youngest athletes (rhythmic gymnastics), even after correction of the logarithm of the concentration by the reciprocal of age. Over the training season, the within-athlete variabilities of IGF-I and P-III-P in elite athletes were low (22.8 % and 21.7 %, respectively). Recreational athletes taking part in a 21 km competition race showed a significant increase in serum values of IGF-I and P-III-P immediately after the event. Exercise workload and age had a significant effect on serum concentration of P-III-P, while age alone affected IGF-I serum concentrations. Therefore, athlete's reference concentration ranges for doping detection should include subjects from as many different ages and sports as possible.