Purpose: We hypothesized that creatine supplementation would facilitate muscle anabolism by increasing the expression of growth factors and the phosphorylation of anabolic signaling molecules; we therefore tested the responses of mRNA for IGF-I and IGF-II and the phosphorylation state of components of anabolic signaling pathways p70(s6k) and 4E-BP1 to a bout of high-intensity resistance exercise after 5 d of creatine supplementation.
Methods: In a double-blind cross-over design, muscle biopsies were taken from the m. vastus lateralis at rest and 3 and 24 h postexercise in subjects who had taken creatine or placebo for 5 d (21 g x d(-1)). For the first 3 h postexercise, the subjects were fed with a drink containing maltodextrin (0.3 g x kg(-1) body weight x h(-1)) and protein (0.08 g x kg(-1) body weight x h(-1)).
Results: After creatine supplementation, resting muscle expressed more mRNA for IGF-I (+30%, P < 0.05) and IGF-II (+40%, P = 0.054). Exercise caused an increase by 3 h postexercise in IGF-I (+24%, P < 0.05) and IGF-II (+48%, P < 0.05) and by 24 h postexercise in IGF-I (+29%, P < 0.05), but this effect was not potentiated by creatine supplementation. The phosphorylation states of p70(s6k) and 4E-BP1 were not affected by creatine at rest; phosphorylation of both increased (150-400%, P < 0.05) to similar levels under placebo and creatine conditions at 3 h postexercise plus feeding. However, the phosphorylation state of 4E-BP1 was higher in the creatine versus placebo condition at 24 h postexercise.
Conclusion: The increase in lean body mass often reported after creatine supplementation could be mediated by signaling pathway(s) involving IGF and 4E-BP1.