A functional polymorphism at the α-actinin-3 (ACTN3) gene includes RR, RX and XX.α-actinin-3 protein is encoded only by RR and RX, with its expression being associated with higher muscle power and strength. However, whether or not the level of α-actinin-3 protein expression determines human performance has not been clarified. The aim of this study was to examine the effect of α-actinin-3 protein expression levels on muscle strength of the knee extensors. Twenty two college level male sprinters (20.7±1.6 y-o, 173.1±5.4 cm, 68.1±5.2 kg) participated in this study. They were genotyped for ACTN3 R577X using real-time polymerase chain reaction method. Subjects performed isometric and isokinetic knee extensions on a dynamometer to evaluate maximum strength at various speeds. After a week, muscle biopsies were obtained from the vastus lateralis muscle to evaluate the level of α-actinin-3 and -2 protein expression and to determine the muscle fiber composition. The level of α-actinin-3 protein expression was significantly higher in RR than RX subjects. However, no significant differences were found in knee extensor strength at any given speed, and in 100m personal best record among ACTN3 genotypes. The level of α-actinin-3 protein expression differed among ACTN3 genotypes, however this difference did not affect muscle strength of the knee extensors in college level male sprinters.

DESCENTE SPORTS SCIENCE Vol.35/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE