Serum IGF-I, IGFBP-3 and ALS concentrations and physical performance in young swimmers during a training season

Abstract Introduction The GH/IGF-I axis is a system of growth mediators, receptors, and binding proteins that regulate somatic and tissue growth; and it has been shown that exercise programs are related to the anabolic function of this axis. Objective The aim of this study was to analyse the changes of serum IGF-I concentration and that of its binding proteins IGFBP-3 and ALS in adolescent swimmers at different stages of a training season, and compare them with physical performance parameters and body composition of the athletes. Material and methods Nine male athletes, aged 16 to 19 years and who trained regularly throughout the season, were included in this study. Serum IGF-I, IGFBP-3, and ALS concentrations were recorded before and after (pre × post) standardized training sessions during the different stages of a training season (extensive × intensive × tapering). Endurance in freestyle, anaerobic fitness in tied swimming (Peak Force and Average Force), body mass, fat percentage, and lean body mass were also analysed at the different stages of training in order to compare the changes of the IGF-I/IGFBP/ALS system with the physical performance and body composition of the athletes. Variations in the IGF-I/IGFBP-3-ALS system before and after a standardized training session, and at the different stages of training were analysed by the Wilcoxon and Friedman non-parametric tests, respectively. Significance was considered at 5%. Results The results from this study demonstrate that IGF-I is sensitive to the acute and chronic effects of training, exhibiting biphasic behaviour throughout the season. The catabolic phase was characterized by a reduction in serum IGF-I concentrations during the intensive stage ( ∆ IGF-I : - 43.33 ± 47.32 ng/ml; P < 0.05) while the anabolic phase was marked by similar basal concentrations at the different stages of training and an increase in post-training serum IGF-I concentrations during the tapering stage (320 ± 40; 298 ± 36 and 359 ± 94 ng/ml; P < 0.05). IGFBP-3 was only sensitive to the chronic effects of training, with a reduction in post-training serum concentrations during the intensive stage and an increase during the tapering stage (4.7 ± 0.7, 4.6 ± 0.4 and 5.0 ± 0.7 mg/l; P < 0.05). No significant difference (P > 0.05) was observed in pre- or post-training IGFBP-3 concentrations ( ∆ IGFBP-3 ) at the different stages. ALS concentrations remained unchanged throughout the season, demonstrating that in adolescent athletes they