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Athletics & FitnessEvidence 1B

rs1815739 · ACTN3

Risk allele: T

Risk-Allele Phenotype

T allele (577X stop codon) produces non-functional alpha-actinin-3 protein; XX genotype lacks functional ACTN3 (R577X null) in fast-twitch muscle fibers, favoring endurance phenotype and reducing power/sprint performance.

Reference-Allele Phenotype

C allele produces functional ACTN3 (R577 wild-type) supporting fast-twitch muscle contractility and power output.

Evidence Level

1BStrong — single high-quality study See methodology for how we grade evidence.

Cross-References

Informational only

This page summarizes population-level evidence about a genetic variant. It is not a diagnosis. Your individual risk depends on your full genome, lifestyle, environment, and family history. Consult a healthcare provider for personalized medical advice.

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