The ACTN3 R577X polymorphism was not associated with differences in power output, fatigability, or force-velocity characteristics in moderately trained individuals.
Cross-Sectional (n=120)
Does the ACTN3 R577X genotype influence muscle power, strength, and fatigability in moderately to well-trained individuals?
The ACTN3 R577X polymorphism is not associated with baseline differences in power output or fatigability in moderately trained individuals, but may modulate responsiveness to training and affect ACTN2 expression.
Alpha-actinins are structural proteins of the Z-line. Human skeletal muscle expresses two alpha-actinin isoforms, alpha-actinin-2 and alpha-actinin-3, encoded by their respective genes ACTN2 and ACTN3. ACTN2 is expressed in all muscle fiber types, while only type II fibers, and particularly the type IIb fibers, express ACTN3. ACTN3 (R577X) polymorphism results in loss of alpha-actinin-3 and has been suggested to influence skeletal muscle function. The X allele is less common in elite sprint and power athletes than in the general population and has been suggested to be detrimental for performance requiring high power. The present study investigated the association of ACTN3 genotype with muscle power during 30-s Wingate cycling in 120 moderately to well-trained men and women and with knee extensor strength and fatigability in a subset of 21 men performing isokinetic exercise. Muscle biopsies were obtained from the vastus lateralis muscle to determine fiber-type composition and ACTN2 and ACTN3 mRNA levels. Peak and mean power and the torque-velocity relationship and fatigability output showed no difference across ACTN3 genotypes. Thus this study suggests that R577X polymorphism in ACTN3 is not associated with differences in power output, fatigability, or force-velocity characteristics in moderately trained individuals. However, repeated exercise bouts prompted an increase in peak torque in RR but not in XX genotypes, suggesting that ACTN3 genotype may modulate responsiveness to training. Our data further suggest that alpha-actinins do not play a significant role in determining muscle fiber-type composition. Finally, we show that ACTN2 expression is affected by the content of alpha-actinin-3, which implies that alpha-actinin-2 may compensate for the lack of alpha-actinin-3 and hence counteract the phenotypic consequences of the deficiency.
Norman et al. (Fri,) conducted a cross-sectional in Healthy moderately to well-trained individuals (n=120). ACTN3 R577X genotype vs. Other ACTN3 genotypes was evaluated on Peak and mean power, torque-velocity relationship, and fatigability output. The ACTN3 R577X polymorphism was not associated with differences in power output, fatigability, or force-velocity characteristics in moderately trained individuals.