How are ACTN3 and Sport related?

The provided context does not contain specific information about ACTN3. Based on extensive scientific literature, ACTN3 encodes alpha-actinin-3, a protein expressed in fast-twitch (type II) muscle fibers. The common R577X variant (rs1815739) results in a null allele. Individuals with the RR or RX genotypes (functional protein) show advantages in power and sprint performance, while the XX genotype (no functional protein) is associated with endurance performance. Evidence is strong (multiple studies, meta-analyses). However, ACTN3 is just one of many factors; training, nutrition, and other genes have greater influence. A genetic test can provide insights but cannot definitively predict athletic success. The effect size is moderate, and clinical utility is limited. Safety note: Do not make medical or training decisions based solely on this gene.