<![CDATA[Fast-twitch muscle performance is an important component in sports requiring strength, speed, and explosive power over a short period, including basketball and futsal. In addition to training, nutrition, and physical condition, genetic variation may contribute to differences in skeletal muscle capacity. One of the most extensively studied genes is ACTN3, which encodes α-actinin-3, a structural protein predominantly expressed in type II muscle fibers. The R577X polymorphism of the ACTN3 gene results in variation in α-actinin-3 expression and has been associated with differences in explosive muscle performance. This study aimed to analyze differences in fast-twitch muscle performance according to ACTN3 gene polymorphism among basketball and futsal athletes at the Faculty of Medicine, Swadaya Gunung Jati University.This analytical observational study used a cross-sectional design involving 26 athletes selected through total sampling. ACTN3 polymorphism was identified through DNA extraction, polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) using the DdeI restriction enzyme, followed by gel electrophoresis. Fast-twitch muscle performance was assessed using a 30-meter sprint test, vertical jump test, and one-repetition maximum (1RM) tests for leg extension, leg curl, hip abduction, and hip adduction. Data were analyzed using the Shapiro–Wilk and Kruskal–Wallis tests.The RX genotype was identified in 14 athletes (53.8%), whereas the XX genotype was found in 12 athletes (46.2%); no RR genotype was detected. The RX group demonstrated higher mean performance values across all fast-twitch muscle tests than the XX group; however, none of the differences were statistically significant (p>0.05).The RX genotype showed a tendency toward better fast-twitch muscle performance, although ACTN3 polymorphism was not significantly associated with performance in this study population.]]>
