The utility of resting levels of IGF-I and IGFBP-3 as markers of training status in elite athletes

Abstract

Insulin-like growth factor-I (IGF-I) and its principle binding protein (IGFBP-3) are believed to play a role in mediating the anabolic effects of exercise. The purpose of this study was to assess the effect of 4 months of training on IGF-I and IGFBP-3, and to determine if changes in IGF-I or IGFBP-3 were related to changes in training status. Twelve varsity swimmers (5 males, 7 females) were tested pre-season, and again after 8 and 16 weeks of training. Measures included: VO2 max, nutritional status, athletic performance, subjective symptoms of overtraining, and serum levels of IGF-I and IGFBP-3. There was no significant change across time in VO2 max, athletic performance, IGF-I or IGFBP-3. Resting IGFBP-3 was positively correlated to symptoms of overtraining at week 0 (p=0.017), however, this relationship did not persist at week 8 or 16. These findings can not confirm that resting levels of IGF-I and IGFBP-3 are sensitive markers of training status.