IGF-I System Responses Following Differing Volumes of Acute Resistance and Aerobic Exercise

Abstract

1663 The literature is equivocal regarding how acute exercise influences IGF-I concentrations with equal numbers of studies reporting increases, decreases, or no changes. We have previously reported that high volume, resistance exercise had no effect on overnight IGF-I, but altered IGF-I regulatory binding proteins (Nindl, JAP, 2001) and suggested that IGFBPs may be sensitive biomarkers of exercise-induced stress. PURPOSE: To examine the hypothesis that IGFBPs, rather than IGF-I itself, would prove to be more responsive to acute exercise stress in a dose-dependent fashion. METHODS: 8 men (24 ± 5 yr, 87 ± 9 kg, 182 ± 6 cm, 21 ± 5 %BF) had blood drawn every 4 hrs post-exercise for 24 hrs and assayed for IGF-I, IGFBPs 1 and 3 and the acid labile subunit (ALS) on 5 occasions, each separated by a month and counterbalanced: control (C; no exercise), moderate volume resistance exercise (MR; 25, 5–10 RM sets), high volume resistance exercise (HR; 50, 5–10 RM sets), moderate volume aerobic exercise (MA; 3, 15-minute cycling bouts @ ∼70 VO2 max) high volume aerobic exercise (HA; 6, 15-minute cycling bouts @ ∼70% VO2 max). Energy requirements were determined from resting metabolic rate, age and a physical activity factor. Dietary control was implemented by providing all meals the day of and the day after the exercise bouts. A two-way ANOVA with repeated measures (p < 0.05) was used for statistical analysis. RESULTS: Significant exercise effects were observed for IGFBP-1 (ng/ml) (C: 14.0 ± 2.7 moderate volume exercise [35 ± 7 ng/ml]). There were no exercise effects for total IGF-I (ng/ml) (C: 346 ± 38; MR: 336 ± 28; HR: 303 ± 40; MA: 327 ± 41; HA: 347 ± 52), IGFBP-3 (ng/ml) (C: 4245 ± 215; MR: 4114 ± 207; HR: 4097 ± 297; MA: 4191 ± 262; HA: 4167 ± 239) or ALS (μg/ml) (C: 14.0 ± 1.2; MR: 15.8 ± 1.5; HR: 15.0 ± 1.6; MA: 15.5 ± 1.3; HA: 15.3 ± 1.2). CONCLUSION: For the circulating IGF-I system components measured, only IGFBP-1 appears to be a sensitive biomarker capable of assessing the physiological strain of acute physical exercise. These data are suggestive that exercise affects IGF-I partitioning among binary molecular complexes in a dose-dependent manner.