The ACE gene: the 'fitness gene' and its endurance vs power I/D variant

An honest sports-genetics guide · Updated August 2026

23andMe & raw DNA

What ACE actually does

Before it was ever a "fitness gene," ACE had a day job — and it's an important one. ACE stands for angiotensin-converting enzyme, and it is a central player in the renin-angiotensin system (RAS), the hormonal cascade that helps regulate your blood pressure and fluid balance.

The short version: ACE converts a molecule called angiotensin I into angiotensin II, a potent signal that narrows blood vessels and prompts the body to retain salt and water. Both effects raise blood pressure. ACE also breaks down bradykinin, a molecule that widens vessels. This is not obscure biology — it's exactly the system that a whole class of common blood-pressure medications, the ACE inhibitors, are designed to block.

So the first thing worth holding onto is that ACE is a cardiovascular and fluid-regulation gene first. Its connection to exercise flows from that role — the same system that manages blood pressure also has a hand in how blood flow, tissue, and metabolism respond to physical demand. That's the biologically plausible thread researchers pulled on when they started asking whether a common ACE variant might nudge athletic performance.

The I/D polymorphism: what the variant is

The variant that made ACE famous is unusual. Most consumer-genetics markers are single-letter changes — one DNA base swapped for another. The ACE variant is different: it's an insertion/deletion, meaning a whole chunk of DNA (a repetitive stretch about 287 bases long) is either present or absent inside the gene.

That gives the polymorphism its name and its two alleles:

• I allele (insertion): the DNA segment is present. Associated with lower circulating ACE enzyme activity.
• D allele (deletion): the DNA segment is absent. Associated with higher ACE enzyme activity in blood and tissue.

Because you inherit one copy from each parent, there are three genotypes:

The link between the deletion and higher enzyme levels is the solid, measurable part of this story — the D allele really does track with more circulating ACE. Everything downstream of that, in the world of performance, is where the certainty drops off fast.

One technical wrinkle worth knowing: because the I/D marker is an insertion/deletion rather than a simple letter swap, genotyping arrays don't always read it cleanly, and it's often studied through nearby "tag" SNPs — markers like rs4340, rs4341, or rs4343 that tend to travel with the I or D allele — or reported under the identifier rs1799752. We'll come back to what that means for finding it in your own file.

The endurance-versus-power association — and how weak it is

Here's the finding that launched a thousand headlines. When researchers compared groups of elite athletes to the general population, they reported a pattern: the I (insertion) allele showed up somewhat more often in endurance athletes — distance runners, rowers, high-altitude mountaineers — while the D (deletion) allele showed up somewhat more often in power and sprint athletes. It fit the biology neatly enough to be irresistible, and the "endurance gene" nickname was born.

The pattern is real in the sense that it has been reported across multiple studies. But look across the whole literature rather than at one striking result, and a much more humbling picture emerges:

• The effect is small. Where the association appears, it's a modest shift in allele frequencies across large groups — the kind of difference you can only see statistically, never something that reliably shows up in one person.
• It's inconsistent. Plenty of studies find the link weakly, in the opposite direction, or not at all. That back-and-forth is the signature of a weak signal, not a strong one.
• It depends heavily on the population. The strength and even the direction of the finding vary with ancestry, the sport, how "elite" is defined, and sample size. Single-gene athletic claims travel notoriously poorly from one group to another.
• The mechanism is still fuzzy. Exactly how ACE activity would translate into endurance or power — through blood flow, muscle efficiency, tissue response, or something else — is not pinned down, which is part of why the performance findings stay soft.

Put bluntly: ACE I/D is real, well-studied, and interesting, and also nowhere near strong enough on its own to tell you what kind of athlete you are. Like ACTN3, it is one thread in a very large fabric. Athletic performance is polygenic — shaped by many genes, each adding a little — and ACE is just one of them.

Why training dwarfs the gene

Even if you granted the ACE association its most generous reading, it would still be a rounding error next to the things that actually build athletic performance. The honest hierarchy of what makes an endurance or power athlete looks like this:

• Training — years of consistent, well-structured work is the single largest factor, by a wide margin.
• Environment and access — coaching, facilities, nutrition, recovery, altitude, and opportunity.
• Body structure — limb proportions, tendon properties, heart and lung capacity, overall build.
• Physiology beyond one gene — the combined pull of many other genes, most of them unmapped.
• Psychology — motivation, resilience, and the plain willingness to keep showing up.

You can find elite endurance athletes who are DD and elite power athletes who are II — carrying the "wrong" genotype for their event and winning anyway. That alone should settle it: the gene is not destiny. It's a small nudge on the odds inside a system dominated by effort and circumstance. If you're curious about your own leanings, the most reliable evidence isn't a DNA letter — it's how your body actually responds to training, which you can only learn by training.

This is also why the direct-to-consumer "sports gene" test deserves real skepticism. Some companies — occasionally marketing to parents of young children — sell ACE-and-ACTN3 panels that promise to reveal a person's "endurance vs power" destiny or ideal sport. The evidence does not support these claims. Major sports-science and genetics bodies have cautioned that using single-gene tests to steer talent identification, or to push a child toward or away from a sport, is not scientifically justified and can do harm: discouraging a kid who would have thrived, or narrowing a young person's world based on a marker that predicts almost nothing about them individually. A responsible reading of ACE is educational, not prescriptive. It is not a scouting tool.

How ACE shows up in your raw data

If you want to look at your own ACE result — understood in the sober terms above — the process is the same as any other marker, with one caveat.

1. Download your raw data from 23andMe or another service.
2. Search the file for the ACE markers. Because the classic I/D insertion/deletion isn't always genotyped directly, look for the tag SNPs that stand in for it — rs4340, rs4341, rs4343 — or the identifier rs1799752.
3. Or use our free DNA explorer — it reads your file in your browser, and nothing is uploaded. (You can also do this without uploading anything anywhere.)

Two honest expectations to set. First, the ACE I/D marker may simply not be present in your file — insertion/deletion variants are harder for genotyping chips to call, so many consumer arrays skip the direct marker and it's inferred from the tags. If none of those rsIDs appear, the variant wasn't on the chip; that's normal, not an error. Second, as with every marker, strand orientation can flip the letters you see between exports. The underlying genotype is the same; the notation just depends on which strand the file reports.

The responsible takeaway

None of this makes ACE boring — quite the opposite. It's a lovely example of how one gene can wear two hats: a workhorse of blood-pressure regulation that also happens to carry a common variant with a faint fingerprint on athletic performance. It teaches the single most important lesson in reading any genetic result — the gap between "associated with" and "determines." A gene can shift the odds across thousands of people while telling you almost nothing about the next individual.

So a grounded reading of your ACE result looks like this:

• Treat your genotype as a fun fact, not a training plan. It's context, not a coaching instruction.
• Remember the enzyme, not just the nickname. ACE's real job is blood-pressure regulation; the "fitness gene" label is a downstream story that's far softer than it sounds.
• Don't let it discourage or over-encourage you. Your response to training is what actually matters, and you can't read it off a chromosome.

If you enjoy this kind of biology, ACE pairs naturally with ACTN3, the 'sprint gene' — real science, oversized reputation, same caveats. Reading both together is a good exercise in holding two ideas at once: the science is genuine, and it's far more modest than the marketing. For the full picture of what your file holds, browse the rest of the Quanome genetics library or the Quanome blog.

Educational only. This article is not medical, diagnostic, or performance advice. 23andMe raw data reports the letters you carry at specific positions in your genome; it does not measure your fitness, muscle, or athletic potential, and it should not be used to make training, career, or health decisions. For anything that matters, work with qualified professionals — and, for athletic questions, with actual training. Quanome reads your DNA on your device and never uploads your genome.

Look up your ACE and other markers privately

Quanome reads your raw DNA on your device and helps you find well-studied markers like the ACE I/D variant — without uploading your genome. Learn more about Quanome →

Frequently asked questions

What is the ACE gene?

ACE stands for angiotensin-converting enzyme. Its everyday job has nothing to do with sport: it is a key part of the renin-angiotensin system that helps regulate blood pressure and fluid balance. It became famous in sports genetics because of a common insertion/deletion (I/D) variant that alters how much of the enzyme circulates, and which shows a weak statistical link to endurance versus power performance.

Is ACE the 'endurance gene'?

It is often nicknamed the 'endurance gene' or 'fitness gene,' but that oversells it. The I (insertion) allele is associated, on average and across large groups, with a modest endurance lean, and the D (deletion) allele with a power/strength lean. For any single person the effect is small and easily swamped by training and everything else. It is one of many genes involved, not a switch that makes you an endurance athlete.

Does the ACE gene make you a better athlete?

No. ACE is associated with a small tilt toward endurance or power at the population level, but it does not determine athletic ability. Training, coaching, body structure, physiology, motivation, and many other genes matter far more. Plenty of elite athletes carry the 'wrong' ACE genotype for their event. A raw-data result is not a talent test.

What is the difference between the ACE I and D alleles?

The variant is a stretch of DNA that is either present (I, insertion) or absent (D, deletion) in the ACE gene. The D allele is associated with higher ACE enzyme activity in blood and tissue, and the I allele with lower activity. That gives three genotypes — II, ID, and DD — with II leaning endurance, DD leaning power, and ID in between. These are statistical tendencies, not verdicts.

Can I check the ACE gene in my 23andMe raw data?

Sometimes, but not always directly. The classic ACE I/D marker is an insertion/deletion that consumer arrays don't always genotype cleanly. It is often looked at through nearby tag SNPs such as rs4340, rs4341, or rs4343, or reported under rs1799752. Search your raw data for those rsIDs, or use a tool that looks them up. If none are present in your file, the marker simply wasn't on the chip.

Is athletic ability genetic?

Partly. Athletic performance is polygenic and heritable to a degree — many genes each contribute a little — but it is overwhelmingly shaped by training, environment, and opportunity. No single gene, including ACE, predicts who will excel. Genetics sets a loose backdrop; consistent training and circumstance write most of the story.

Should I choose a sport based on my ACE result?

No. Single-gene 'sports gene' tests that promise to reveal your ideal event or a child's athletic destiny are not supported by the evidence. ACE explains very little about any individual, and steering someone toward or away from a sport on that basis risks real harm. Enjoyment, access, and consistent training are far better guides.

Is 23andMe raw data a fitness or diagnostic test?

No. Raw genotyping data reports which letters you carry at specific positions in your genome. It is not a medical test, a fitness assessment, or a measure of athletic potential, and it should not be used to make training, career, or health decisions. Treat markers like ACE as educational context and rely on qualified professionals and actual training for anything that matters.

Quanome is live — free on iPhone and Android

Make sense of your DNA and health data privately. Download Quanome free on the App Store or Google Play.

Quanome is free on the App Store and Google Play. Want product news too? Leave your email below.

Email me updates

I agree to receive occasional product updates and news from Quanome by email. See our Privacy Policy.