What role does ACTN3 play in Sport?

The provided context does not contain information about ACTN3. Based on established research, ACTN3 encodes α-actinin-3, a protein expressed in fast-twitch muscle fibers. The common R577X polymorphism results in a loss of function. The RR and RX genotypes are associated with sprint and power performance, while the XX genotype may be overrepresented in endurance athletes. Evidence is human-strong, with multiple meta-analyses confirming these associations (e.g., PMID 17928227, 23988819). However, the effect size is modest; genetics alone cannot determine athletic success. Training, nutrition, and other factors are more influential. Consumer DNA tests can report this variant, but results should be interpreted cautiously and not as a definitive predictor.