Response of High-Affinity Growth Hormone Binding Protein to Acute Heavy Resistance Exercise

Abstract

1664 PURPOSE: The purpose of this investigation was to examine the effects of acute and chronic heavy resistance exercise on circulating concentrations of growth hormone binding protein (GHBP). METHODS: Using a cross-sectional experimental design, a group of resistance-trained men (N = 9) with at least five years of resistance training N = experience (mean ± SE years experience: 7.94 ± 1.31) and a group of untrained men (N = 10) performed an acute heavy resistance exercise protocol (6 sets of 10 repetition N = maximum parallel squats). Blood samples were obtained 72-hours prior to exercise, immediately prior to exercise, as well as 0, 15, 30, 45, and 60 minutes post-exercise. RESULTS: Significant (P: <0.05) resistance-exercise induced increases in GHBP, immunoreactive growth hormone, and IGF-1 were observed in both subject groups. No significant differences in GHBP were observed between groups either at rest or post-exercise. Resistance-trained men exhibited a significantly greater iGH response to acute resistance exercise than untrained subjects. Resistance-trained men exhibited significantly higher IGF-1 than untrained subjects at rest and post-exercise. Significant positive correlations were observed between GHBP and BMI, body fat, and leptin. A significant positive correlation was also observed between resting leptin and GHBP in the untrained subjects, whereas this relationship was not observed in the trained subjects. CONCLUSIONS: These data indicate that resistance training does not increase blood GHBP, thus indicating no change in GH receptor expression after training despite increases in IGF-1, which may indicate greater hepatic GH sensitivity. However, other factors that strongly influence blood GHBP, including leptin and adipose cells, may mask training-induced increases in circulating GHBP.