Alpha-actinin-3 (ACTN3) R577X polymorphism influences knee extensor peak power response to strength training in older men and women

Background. The alpha-actinin-3 (ACTN3) R577X polymorphism has been associated with muscle power performance in cross-sectional studies. Methods. We examined baseline knee extensor concentric peak power (PP) and PP change with ~10 weeks of unilateral knee extensor strength training (ST) using air-powered resistance machines in 71 older men (65 [standard deviation = 8] years) and 86 older women (64 [standard deviation = 9] years). Results. At baseline in women, the XX genotype group had an absolute (same resistance) PP that was higher than the RR (p = .005) and RX genotype groups (p = .02). The women XX group also had a relative (70% of one-repetition maximum [1-RM]) PP that was higher than that in the RR (p = .002) and RX groups (p = .008). No differences in baseline absolute or relative PP were observed between ACTN3 genotype groups in men. In men, absolute PP change with ST in the RR (n = 16) group approached a significantly higher value than in the XX group (n = 9; p = .07). In women, relative PP change with ST in the RR group (n = 16) was higher than in the XX group (n = 17; p = .02). Conclusions. The results indicate that the ACTN3 R577X polymorphism influences the response of quadriceps muscle power to ST in older adults.