Are Athletes Born or Made? What the Science Says

What makes someone naturally good at sport?

Athletic performance is not one trait. It is several systems working together, and each of them varies between people. Sports genetics research has identified specific genes influencing each system, none decisive on its own, which is exactly the point.

Muscle fibre type: ACTN3

Skeletal muscle contains fast-twitch fibres, which produce force quickly and fatigue quickly, and slow-twitch fibres, which produce less force but resist fatigue. Everyone has both. The proportions vary between people, and they bias you towards sprinting and jumping or towards endurance.

ACTN3 codes for a protein called alpha-actinin-3, which is found only in fast-twitch fibres. The gene comes in two versions:

• R: the working version, which produces the protein
• X: a version carrying a premature stop signal, which produces none of it

You inherit one copy from each parent, so there are three possible combinations:

• RR: two working copies, most alpha-actinin-3
• RX: one working copy
• XX: no working copies, and therefore no alpha-actinin-3 in your muscle at all

The XX result sounds alarming and is not. It is not a disease, and it is common: around 18% of people of European descent and roughly 25% of people of East Asian descent are alpha-actinin-3 deficient, which is somewhere between one in four and one in six. Most of them will never notice.

With that in place, the association makes sense. A meta-analysis of 25 studies across 13 countries, covering 14,541 people, found that power athletes were about 1.48 times more likely than non-athletes to carry RR, the two-working-copy version, and comparing power athletes with endurance athletes, RR appeared about 1.27 times more often.

Oxygen delivery: ACE and VEGFA

Getting oxygen to working muscle is the limiting factor in endurance events. ACE influences blood flow regulation, with different variants associated with endurance and with strength. VEGFA governs the formation of new blood vessels, which is how the body increases delivery capacity in response to training.

Energy production: PPARGC1A

Mitochondria convert nutrients into usable energy, and PPARGC1A is a master regulator of how many of them you build in response to endurance training. It is one of the more mechanistically well understood genes on this list.

Connective tissue and injury: COL5A1 and COL1A1

These code for collagen, the structural protein in tendons and ligaments, and this is arguably the most practically useful area of sports genetics.

Recovery and inflammation: IL6 and TNF

These influence the inflammatory response to hard training, which is the process that drives both adaptation and soreness. Variation here is part of why two people on the same programme can need noticeably different amounts of recovery, a real and common source of frustration, particularly for people training with a partner who seems to bounce back faster.

Trainability itself

This is the finding most people have never heard, and it may be the most important.

The HERITAGE Family Study put 481 sedentary adults from 98 families through the same supervised 20-week programme. Average gain in aerobic capacity was around 400 ml/min, but individuals ranged from almost no improvement to over 1,000 ml/min on identical training. The response ran in families, with heritability of the training response estimated at up to 47%.

So it is not only where you start. How steeply you improve is partly inherited too.

Is there a "super athlete" gene?

No, and anyone selling you one is misreading the science.

Look at the effect sizes above. ACTN3 gives odds ratios around 1.3 to 1.5. COL5A1 sits around 1.2 to 1.5. These are real, replicated, population-level associations. They are also nowhere near large enough for any single one of them to determine anything about a specific person. Plenty of elite power athletes carry the "wrong" ACTN3 variant. Plenty of people with the "right" one never compete at all.

Athletic ability is polygenic. It emerges from many variants each contributing a small amount, interacting with training, nutrition, opportunity and luck. That is why a panel looks at several genes across several systems rather than one, and why the useful output is a picture of your physiology rather than a verdict on your potential.

How much does training actually matter?

A great deal, though less than the "10,000 hours" idea claims, and the correction is more interesting than the myth.

A meta-analysis of 88 studies covering 11,135 participants found deliberate practice explained 18% of the variance in sports performance.

That number is used badly in both directions. It is smaller than the popular claim, so practice is clearly not the whole story. But 18% is substantial for any single factor, and the remaining 82% is not all genetics, it includes coaching quality, starting age, access to facilities, psychology, injury luck and measurement error.

And people write themselves off far too early. In a randomised trial, 69% of participants looked like non-responders to training on 60 minutes a week. At 240-300 minutes a week, none did. When the original non-responders were given more training, every single one responded. Much of what looks like a genetic ceiling turns out to be a training dose.

Can you tell whether you are built for power or endurance?

Partly, and it takes two different kinds of information, which answer two different questions.

A performance test tells you where you are now. A sprint profile, a vertical jump, a lactate or aerobic capacity test, these measure what your physiology currently does, which is your genetics, training history and current condition combined into one number. This is what tells you which capacity is limiting you today and whether your training is working.

A genetic test tells you about the machinery underneath. Which fibre type your muscle is built around, how your body regulates oxygen delivery and builds mitochondria, how your connective tissue is constructed, how strongly you inflame after hard sessions. That does not change with training, and it does not tell you what you can become, but it is the context that makes your performance results legible.

Used together they answer different halves of the question. Used alone, a genetic result is background biology and a performance test is a snapshot without explanation.

The Phenome Sports Performance test reports across all of these systems: ACTN3, ACE, PPARGC1A, VEGFA, the collagen genes, and the inflammatory genes. Each contributes a small part. The value is in the combination, and in understanding the biology you are training rather than guessing at it.

→ Explore the Sports Performance Test
→ How to Train Smarter for Your Body

So, are elite athletes born or made?

Both, and which one dominates depends on the question you are actually asking.

To reach the very top of a global sport: genetics matters enormously. Elite competition selects on the extreme tail of human physiology, and everyone there has both unusual biology and an enormous volume of high-quality training, plus the opportunity to accumulate it.

To reach your own potential: training dominates, and it is not close. Almost nobody trains near their own ceiling. For essentially everyone reading this, the constraint is not the genome, it is consistency, dose, sleep and food.

Genetics sets the range you are working within. Training determines where inside it you land. Most people never discover where their range ends, because they stop long before reaching it.

→ How to Improve Your Athletic Performance: The Complete Guide
→ What Determines Athletic Performance?
→ Why Recovery Matters for Performance
→ Genetic Testing for Health: The Complete Guide