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Excerpt
PURPOSE: This study investigated the effects of 40 weeks of resistance training on circulating levels of IGF-1 and IGF binding protein-3 (BP3) in 57–70 year old men (n = 47) and women (n = 79). METHODS: The resistance training consisted of 5 upper body and 7 lower body exercises performed on Cybex isotonic equipment. The subjects were split into four training groups with varying levels of relative intensity (40% vs. 80% 1-RM) and different frequencies of training (2 vs. 3 days/week). Serum IGF-1 and BP3 were assessed at baseline, 20 weeks, and 40 weeks of training by commercial radioimmunoassay kits (Diagnostic Systems Laboratory). The intra-assay variation for both IGF-1 and BP3 assays ranged from .05 to 12%, while the inter-assay variation ranged from .2 to 14%. RESULTS: There were significant gender differences (p<.05) in IGF-1 with women having significantly lower levels than men. There was a significant trial effect (p = .032) for IGF-1. IGF-1 significantly decreased from baseline to 20 weeks (154 ng/ml to 136 ng/ml, p = .025) followed by an increase at 40 weeks (136 ng/ml to148 ng/ml, p = .038). There were trends for gender differences in the IGF-1 relative changes with men showing a 11.9 % increase and women showing an 8.1% decrease from baseline to 20 weeks (p = .053). Men tended (p = .059) to have a greater increase from baseline to 40 weeks compared to women (26.2% vs 1.6%). There were no significant trial, gender or training group effects detected for BP3.
CONCLUSIONS: Women had significantly lower serum IGF-1 levels than men at each time point. Although there were no training group differences in IGF-1 responses, IGF-1 decreased at 20 weeks then returned to baseline levels at 40 weeks. Resistance training did not appear to affect BP3 levels.
