EFFECTS OF STRENGTH TRAINING ON BODY COMPOSITION, FASTING INSULIN, AND INSULIN-LIKE GROWTH FACTOR-I

Abstract

Physically active individuals may have decreased risk for cancers of hormonally related etiology, such as breast and colon. Exercise may decrease incidence of these cancers by lowering total and/or bioavailable serum insulin-like growth factor one (IGF-I). IGF-I and its binding proteins (IGFBPs) have been associated with increased risk for breast and colon cancers. PURPOSE: To investigate exercise-induced changes in: IGF-I and IGF-I/IGFBP-3 (as surrogate for bioavailable IGF-I). We compared changes of these variables in women who were lean (n = 28) to those who were overweight (n = 27) at baseline (DEXA assessed body fat %: lean < 39% < overweight). METHODS: 55 healthy women, 30–50 years old, completed this randomized controlled trial, which involved 15 weeks of supervised progressive strength training (2/week, 27 sets/session, 8 to 10 rep. max.), and 24 additional weeks unsupervised. Subjects refrained from change in diet and other activity regardless of group assignment. Measurements were taken at baseline, 15 and 39 weeks. RESULTS: See table 1. By 15 weeks, the overweight subjects also had significant increases in lean mass, no change in fat mass, and significant decreases of fasting insulin. By 39 weeks, levels of IGF-I and IGF-I/IGFBP-3 rose to match controls in overweight subjects, despite further improvements in lean mass and fasting insulin as well as significant fat mass losses. In lean subjects, IGF-I and IGF-I/IGFBP-3 returned to baseline levels by 39 weeks.Table 1: Change at 15 weeks, *p < 0.03 compared to control groupCONCLUSION: 15 weeks of supervised strength training produced significant improvements IGF-I and IGF-I/IGFBP-3 in overweight women, concurrent with improvements in lean mass and fasting insulin. The IGF-I changes were not maintained an additional 24 weeks. Supported by: MNOC, NIH grant 1 P30-DK50456 and UMN GCRC, NIH grant # M01-RR00400