IGF-I System Responses During 12 Weeks of Resistance Training in End-Stage Renal Disease Patients

Abstract

2075 Early cross-sectional observations that circulating IGF-I was associated with fitness level suggested that chronic physical training would favor anabolic processes by increasing circulating IGF-I. However, recent studies have shown that IGF-I is actually decreased in response to short-term training. More information is required to verify this hypothesis especially across a range of healthy vs. unhealthy populations. PURPOSE: To examine the hypothesis that 12 weeks of resistance training would alter circulating concentrations of IGF-I system components in end-stage renal disease (ESRD) patients. METHODS: Ten ESRD patients (42.8 ± 4.6 yr, 172.7 ± 3.2 cm, 90.0 ± 4.9 kg, duration of dialysis treatment 41.6 ± 19.0 months) underwent 12 weeks of resistance training after a 6 week control period and had fasted morning blood samples drawn on 4 occasions (weeks −6, 0, 6, 12). Training consisted of two sessions per week of eight to nine whole body exercises, utilizing 10 to 15 repetitions per set with progressive increases in volume and resistance. Immunoassays were performed for serum total and free IGF-I, IGF binding protein (IGFBP) −2 and −3, acid labile subunit (ALS), and growth hormone binding protein (GHBP). Immunoaffinity depletion of ALS-based complexes allowed measurement of non-ternary (i.e., binary) IGF-I and IGFBP-3. RESULTS: All IGF-I measures were stable during the control period (week −6 to 0) and no changes were observed for the first 6 weeks of resistance training. At week 12, significant (p ≤ 0.05) reductions from week 0 values were demonstrated for total IGF-I (320.2 ± 43.2 vs. 267.1 ± 41.0 ng/mL), ternary IGF-I (253.7 ± 39.1 vs. 206.2 ± 36.5 ng/mL), and the IGF-I/IGFBP-3 molar ratio (2.4 ± 0.2 vs. 1.9 ± 0.3). No differences (p > 0.05) existed for free IGF-I, IGFBP-2, IGFBP-3, ALS, or GHBP. The proportion of IGF-I in ternary (∼76.3 ± 6.8%), non-ternary (∼22.5 ± 6.6%), and free (∼1.2 ± 0.5%) forms remained stable throughout the training. Significant improvements in strength (e.g., isokinetic peak torque of leg extensors) and functional performance (e.g., maximum walking speed and distance covered in 6 minute walk) were also observed. CONCLUSION: 12 weeks of resistance training in ESRD patients induced a decline in total IGF-I, but did not alter the proportion of IGF-I circulating in free, ternary or non-ternary molecular complexes. The decline in IGF-I occurred in the presence of positive training adaptations as measured by physical performance outcome variables. We conclude that the decline of circulating IGF-I during 12 weeks of training, despite being suggestive of a catabolic state, appears to be reflective of favorable neuromuscular anabolic adaptations.