Effect of creatine supplementation and resistance-exercise training on muscle insulin-like growth factor in young adults

The purpose of this study was to compare changes in muscle insulin-like growth factor-1 (IGF-1) content resulting from resistance-exercise training (RET) and creatine supplementation (CR). Male (n = 24) and female (n = 18) participants with minimal resistance-exercise-training experience (>= 1 year) who were participating in at least 30 min of structured physical activity (i.e., walking, jogging, cycling) 3-5 x/wk volunteered for the study. Participants were randomly assigned in blocks (gender) to supplement with creatine (CR: 0.25 g/kg lean-tissue mass for 7 days; 0.06 g/kg lean-tissue mass for 49 days; n = 22, 12 males, 10 female) or isocaloric placebo (PL: n = 20,12 male, 8 female) and engage in a whole-body RET program for 8 wk. Eighteen participants were classified as vegetarian (lacto-ovo or vegan; CR: 5 male, 5 female; PL: 3 male, 5 female). Muscle biopsies (vastus lateralis) were taken before and after the intervention and analyzed for IGF-1 using standard immunohistochemical procedures. Stained muscle cross-sections were examined microscopically and IGF-1 content quantified using image-analysis software. Results showed that RET increased intramuscular IGF-1 content by 67%, with greater accumulation from CR (+78%) than PL (+54%; p = .06). There were no differences in IGF-1 between vegetarians and nonvegetarians. These findings indicate that creatine supplementation during resistance-exercise training increases intramuscular IGF-1 concentration in healthy men and women, independent of habitual dietary routine.