Abstract: Kikuchi, N, Nakazato, K, Min, S-k, Ueda, D, and Igawa, S. The ACTN3 R577X polymorphism is associated with muscle power in male Japanese athletes. J Strength Cond Res 28(7): 1783–1789, 2014—In this study, we investigated whether the ACTN3 R577X polymorphism is associated with muscular power in Japanese collegiate athletes by analyzing the mean and peak power results of a 30-second Wingate anaerobic test (WAnT) with respect to the ACTN3 R577X genotype in 253 Japanese athletes (144 men and 109 women). Each athlete performed a 30-second WAnT with a resistance equal to 7.5% of his or her body weight. Genotyping for the ACTN3 R577X (rs1815739) polymorphism was performed using the TaqMan approach. The ACTN3 R577X genotypes exhibited a Hardy-Weinberg equilibrium distribution in our population. The relative and absolute mean power results of the 30-second WAnT did not differ significantly among the genotypes. However, the relative peak power result of the WAnT was significantly higher in the R-allele-dominant model groups than in the XX group in male but not female athletes. These results suggest that the ACTN3 R allele is associated with the relative peak power during the WAnT in male Japanese collegiate athletes.