Standard
Muscle fiber type ("sprinter gene")
ACTN3 · rs1815739
What each result means
C/C
Two copies of the allele that produces functional alpha-actinin-3. Published research associates this genotype with a higher proportion of fast-twitch muscle fibers, more common among elite power/sprint athletes.
C/T
One functional and one non-functional copy. Published research associates this genotype with a mix of fast- and slow-twitch muscle fiber characteristics.
T/T
Two copies of the variant that produces no alpha-actinin-3 protein. Published research associates this genotype with a higher proportion of slow-twitch muscle fibers, more common among endurance athletes — this is a common, normal variant, not a deficiency.
Source: Yang et al. 2003, American Journal of Human Genetics — ACTN3 genotype and elite athlete status.
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