The Effects of Recombinant Human Insulin-Like Growth Factor-I/Insulin-Like Growth Factor Binding Protein-3 Administration on Body Composition and Physical Fitness in Recreational Athletes

CONTEXT: IGF-I is thought to mediate many of the anabolic actions of GH, and there are anecdotal reports that IGF-I is misused by elite athletes. There is no published evidence regarding the effects of IGF-I administration on athletic performance. OBJECTIVE: The objective of the study was to investigate the effects of IGF-I administration on body composition and physical fitness in recreational athletes. DESIGN AND SETTING: This was a randomized, double-blind, placebo-controlled recombinant human (rh) IGF-I/rhIGF binding protein (IGFBP)-3 administration study at Southampton General Hospital (Southampton, United Kingdom). PARTICIPANTS: Fifty-six recreational athletes (30 men, 26 women) participated in the study. INTERVENTION: Participants were randomly assigned to receive placebo, low-dose rhIGF-I/rhIGFBP-3 (30 mg/d), or high dose rhIGF-I/rhIGFBP-3 (60 mg/d) for 28 days. Body composition (assessed by dual energy x-ray absorptiometry) and cardiorespiratory fitness (assessed by incremental treadmill test) were measured before and immediately after treatment. Within-individual changes after treatment were analyzed using paired t tests. RESULTS: There were no significant changes in body fat mass or lean body mass in women or men after the administration of the rhIGF-I/rhIGFBP-3 complex. There was a significant increase in maximal oxygen consumption (VO2 max) after treatment. When women and men and low- and high-dose treatment groups were combined, mean VO2 max increased by approximately 7% (P = .001). No significant change in VO2 max was observed in the placebo group. CONCLUSIONS: rhIGF-I/rhIGFBP-3 administration for 28 days improves aerobic performance in recreational athletes, but there are no effects on body composition.