Effect of exercise mode and intensity of sub-maximal physical activities on growth hormone and insulin-like growth factor-1 in active young men

Abstract

Aim. The purpose of this study was to determine and compare the effects of intensity and exercise mode on the 5 acute-response of growth hormone (GH), insulin-like growth factor 1 (IGF 1), and IGF-binding protein 3 (IGF-BP3) in active young men. Methods. Ten healthy active young men with average age of 24 +/- 3.69 years participated voluntarily in this study. They underwent a total of six activity sessions on three different devices: elliptical, cycle ergometer, and treadmill, at two different intensities. On three sessions, intensity of activity reached 70% of their maximum heart rate (MHR) and on the other three sessions, reached to 85% of their MHR. Blood samples (5 cc) were taken from the antecubital vein before and right after physical activity. The concentrations of growthhormone and IGF-binding protein 3 were measured using the ELISA method; IGF-1 concentrations were measured using a chemiluminescence assay. Results. ANOVA with repeated measurements revealed a significant increase in the concentration of growth hormone when subjects exercised at intensity of 70% of MHR on treadmill (P=0.037) and cycle ergometer (P=0.015), and at intensity of 85% of MHR on cycle ergometer (P<0.001) and elliptical (P=0.043). The ratio of GH to IGF-1 increased significantly in response to activity at 70% intensity on cycle ergometer (P=0.013) and treadmill (P=0.030), and in response to activity at 85% on the cycle ergometer (P=0.010). Conclusion. The acute response of GH and its ratio to IGF-1 are dependent on both intensity of exercise and exercise mode, while changes in IGF-1 and IGFBP-3 are independent of these two factors.