Endocrine Abstracts

Background: Regular physical exercise during childhood and adolescence can promote growth and development of muscle and bone mass. Although physical exercise is closely linked to the anabolic function of the GH /IGF-I axis the real impact of resistance training on GH/IGF axis is still unclear. The kinetics of IGF-I and IGFBP-3 during chronic training is not fully understood yet and an initial catabolic phase followed by an later anabolic phase has been reported in swimmers.

Aim: The aim of the present study was to analyse the kinetics of IGF-I and IGFBP-3 in adolescents undergoing ten weeks of hypertrophy training.

Methods: Twenty-two male volunteers aged 18–25 years with at least 6 month experience in resistance training were enrolled and submitted to a standard hypertrophy training program during 10 weeks. Serum IGF-I and IGFBP-3 concentrations were determined before, 30 min-after and 24h-after the training session at the 1st, 5th and 10th week of resistance training. Body composition, lean mass, muscle mass, fat percentage and body mass index were also evaluated at the 1st, 5th and 10th week and compared to the changes in serum IGF-I and IGFBP-3. Data were paired compared.

Results: IGF-I levels increased during the training session at the 1st evaluation (P=0.03) and also increased during the 10 weeks of training (P<0.003). No changes in IGFBP-3 levels were observed during a training session or during the 10 weeks of training. Body mass, lean mass, fat percentage and body mass index of the volunteers remained unchanged throughout the 10 weeks of training. A negative correlation was observed between the changes in serum IGF-I concentrations and the variation in muscle mass or lean mass when data from the 1st and the 10th weeks were compared (r=−0.62; P=0.002).

Conclusion: In summary, no catabolic phase was detected in adolescents during hypertrophy training; IGF-I was sensitive to the acute and chronic effects of resistance training and can be considered as a biomarker of training status in non-athlete volunteers. The negative correlation between the variations in lean mass and IGF-I could suggest a training-induced increase in IGF-I sensitivity.