The individual and combined influence of ACE and ACTN3 genotypes on muscle phenotypes before and after strength training

measures of muscle size, strength, and power to those used in previous studies could help resolve the controversy surrounding associations between polymorphisms of the angiotensin-1 converting enzyme (ACE) and a-actinin-3 (ACTN3) genes and skeletal muscle phenotypes, and the responses to resistance training (RT). To this end, we measured quadriceps femoris muscle volume (V.), physiological cross-sectional area (PCSA), maximum isometric force (F-1), specific force (F, per unit PCSA), maximum isoinertial strength (1-RM), and maximum power (W-max; n = 40) before and after 9-week knee extension RT in 51 previously untrained young men, who were genotyped for the ACE UD and ACTN3 R577X polymorphisms. ACTN3 R-allele carriers had greater V-max, 1-RM, and W-max. than XX homozygotes at baseline (all P < 0.05), but responses to RT were independent of ACTN3 genotype (all P> 0.05). Muscle phenotypes were independent of ACE genotype before (all P> 0.05) and after RT (all P> 0.01). However, people with the "optimal" ACE+ACTN3 genotype combination had greater baseline 1-RM and W-max,ax compared to those with the "suboptimal" pmfile (both P< 0.0125). We show for the first time that the ACTN3R577X polymorphism is associated with human V. and (independently and in combination with the ACE UD polymorphism) influences 1-RM and W-max.