ACTN3 rs1815739: the 'sprint gene'
ACTN3 rs1815739 is the variant the press loves to call the "sprint gene" or "speed gene." It really does relate to muscle fiber type — but the headlines oversell it. Here's what it actually is, how to find it in your 23andMe or AncestryDNA raw data, and how much (and how little) it tells you.
What ACTN3 does
ACTN3 produces alpha-actinin-3, a structural protein found specifically in fast-twitch muscle fibers — the ones responsible for explosive, powerful movements like sprinting and jumping.
The rs1815739 variant (R577X) decides whether you make the protein at all:
- C allele (R577): functional — you produce ACTN3.
- T allele (X577): a stop codon — this copy produces no ACTN3.
What the genotypes are associated with
| Genotype | ACTN3 protein | Associated tendency |
|---|---|---|
| CC | Two working copies | Power/sprint lean; over-represented in elite sprinters |
| CT | One working copy | A mix of power and endurance |
| TT | None | Endurance lean; over-represented in elite endurance athletes |
Roughly 18% of people worldwide are TT and make no ACTN3 at all — with no ill effects, since other proteins compensate. Studies of elite athletes show clear statistical enrichment (more CC in sprinters, more TT in marathoners), but at the individual level it's a weak predictor.
How to find rs1815739 in your raw data
- Download your raw data (or from AncestryDNA / MyHeritage).
- Search it for
rs1815739and read your genotype. - Or use our free DNA explorer — it reads your file in your browser, nothing uploaded.
Strand note: 23andMe usually reports rs1815739 on the C/T strand (C = functional, T = stop).
What it does and doesn't tell you
ACTN3 is a fun, harmless marker and a real example of genotype-to-trait biology. But it will not tell you whether you can be fast, strong, or athletic — training and dozens of other factors dominate. Treat it as trivia, not a training plan.
For everything else hiding in your file, see our complete guide to analyzing 23andMe raw data, or browse the rest of the Quanome blog.
Find your ACTN3 and other markers privately
Quanome reads your raw DNA on your device and surfaces well-studied markers like ACTN3 — without uploading your genome. Learn more about Quanome →
Frequently asked questions
What does ACTN3 rs1815739 tell you?
ACTN3 makes a protein found in fast-twitch muscle fibers used for explosive power. The rs1815739 variant determines whether you produce it: the C allele is functional (power/sprint), while the T allele is a stop codon that produces none.
Which ACTN3 genotype is the 'sprinter' type?
CC means two working copies of ACTN3 — common in elite sprinters and power athletes. TT means no ACTN3 protein at all — more common in elite endurance athletes. CT is a mix of both.
How do I find ACTN3 rs1815739 in my raw data?
Search your raw DNA file for rs1815739 and read the two-letter genotype, or use a tool that looks it up. 23andMe typically reports this marker on the C/T strand.
Does ACTN3 determine athletic ability?
No. It nudges a tendency toward power vs endurance, but training, body type, motivation, and many other genes matter far more. Plenty of strong athletes have the 'wrong' genotype for their sport. It is not a verdict.
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