The purpose of this study was to compare changes in muscle insulin-like growth factor-I (IGF-I) 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 ×/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-I using standard immunohistochemical procedures. Stained muscle cross-sections were examined microscopically and IGF-I content quantified using image-analysis software. Results showed that RET increased intramuscular IGF-I content by 67%, with greater accumulation from CR (+78%) than PL (+54%; p = .06). There were no differences in IGF-I between vegetarians and nonvegetarians. These findings indicate that creatine supplementation during resistance-exercise training increases intramuscular IGF-I concentration in healthy men and women, independent of habitual dietary routine.
Burke is with the Dept. of Human Kinetics, St. Francis Xavier University, Antigonish, NS, Canada. Candow is with the Faculty of Kinesiology and Health Studies, University of Regina, Regina, SK, Canada S4S 0A2. Chilibeck is with the College of Kinesiology, University of Saskatchewan, Saskatoon, SK, Canada S7N 5B2. MacNeil is with the Dept. of Kinesiology, and Tarnopolsky, the Dept. of Pediatrics and Medicine, McMaster University, Hamilton, ON, Canada. Roy is with the Dept. of Physical Education and Kinesiology, Brock University, St. Catharines, ON, Canada. Ziegenfuss is with the Ohio Research Group, Wadsworth Medical Center, Wadsworth, OH.