Alpha-actinin-3 R577X Genotype and Muscle Power in Young Male Adults of the Leuven Genes for Muscular Strength Study

Abstract

A polymorphism in the alpha-actinin-3 (ACTN3, C to T) gene results in complete loss of a Z disk protein in fast-contracting myofibers. The ACTN3 genotype (R577X) has been found to be associated with performance in Australian elite athletes and responses to training, however, little is known about the importance of this polymorphism in the interindividual variation of strength and power in the general population. PURPOSE: To study the association of the R577X ACTN3 genotype with muscle strength and power in young male adults. It was hypothesized that X allele carriers showed lower (relative) dynamic and maximal strength. METHODS: The R577X ACTN3 polymorphism (rs1815739, Sequenom MassARRAY SNP) was typed in 362 males (23.4 +/− 4.1 yr) of the Leuven Genes for Muscular Strength Study. Knee extension/flexion torques at 60° and 30° flexion were measured at velocities of 0°/sec, 60°/sec, 120°/sec and 240°/sec. Relative dynamic torques to isometric contractions ratios were computed. Also handgrip strength, arm pull and standing broad jumps were measured. Genotype-phenotype effects were tested using AN(C)OVA with estimated muscle+bone cross-sectional area of thigh (or arm) as covariate. RESULTS: Lack of ACTN3 (X/X carriers) was observed in only 15.5% of these males (X frequency 0.40, no violation of HWE). No association was found with isometric or dynamic knee flexion/extension torques, hand grip, arm pull or standing broad jump strength. Only for the relative dynamic torque ratios (extension at 120°/sec and 240°/ sec), X/X carriers seemed to perform at a lower relative torque compared to X/R or R/R genotypes (p<0.05). Also X/X genotype carriers had smaller estimated muscle+bone cross-sectional areas of thigh and arm (p<0.04). CONCLUSIONS: In a young adult male population, individuals lacking the ACTN3 protein, showed no significant difference in maximal isometric or dynamic knee torque compared to R/X or R/R carriers, however, a lower relative dynamic torque at higher contraction speeds might indicate a downward shift of the force-velocity curve in subjects lacking the ACTN3 protein. The project, GDM and AW supported by FWO Grant 1.5.187.05, G.0496.05 and OT/04/44.