Are you built for power or endurance?

Stand an Olympic sprinter next to a marathon runner and you are looking at two different engines. One releases enormous force in under ten seconds. The other holds a steady pace for more than two hours. Both have trained for years, but they did not start from the same place.

In elite sport, you see that gap every day. Athletes follow near-identical programmes and progress at very different rates. Some thrive on heavy lifts and short, explosive efforts; others only come alive once the sessions get long. The reason sits in their muscle fibres, their mitochondria and the genes that build them.

The same pattern holds outside elite sport. Put a group of people on the same training plan and some improve dramatically while others barely move. Research suggests genetics accounts for a large share of that difference.

Most training advice is written for the average person, and nobody is the average person. Knowing whether your body leans towards power or endurance tells you where your training hours will pay back the most.

This article explains:

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Power and endurance, defined

Every body can build both power and endurance. Your genes decide which one returns more for the same hours of work.

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Three things decide how you respond

Before the genes, the biology. Three systems shape whether your body leans towards power or endurance.

Each of these systems runs on proteins, and each protein is built from a gene. Small differences in those genes create real differences in how you train.

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The three genes that matter most

ACE: the blood pressure gene

Long name: angiotensin-converting enzyme

What it does: controls blood pressure and the balance of fluid and sodium in your blood. ACE is the most researched gene in sports performance: a 1998 study in Nature was the first to link a single gene to human physical performance.

Sports connection: power or endurance, depending on your genotype

The I version shows the most consistent link: it appears more often in elite endurance athletes and in mountaineers who climb above 8,000 metres without supplemental oxygen. The link between the D version and power is less consistent.

ACTN3: the sprinter gene

Long name: alpha-actinin-3

What it does: builds a structural protein inside your fast-twitch muscle fibres

Sports connection: power or endurance, depending on your genotype

Your muscles contain two main fibre types. Slow-twitch fibres power long, steady efforts. Fast-twitch fibres fire hard and fast for sprints, jumps and heavy lifts, but tire quickly.

ACTN3 builds alpha-actinin-3, a protein found almost only in fast-twitch fibres. The protein works like scaffolding inside each fibre, anchoring the parts that contract and holding them steady when they fire with maximum force.

The gene comes in two versions. The R version makes working alpha-actinin-3. The X version carries a small error that stops production, so it makes none. You inherit one version from each parent, which gives you one of three combinations. Some DNA reports label them by the DNA letters at that point in the gene instead: CC, CT or TT.

Why XX is not a weakness

Around one in five people of European descent carry XX, and they live perfectly healthy lives. Without alpha-actinin-3, their fast-twitch fibres take on some slow-twitch traits: slightly less peak power, but more resistance to fatigue.

The effect is real but small. ACTN3 explains only a small share of the differences between athletes, and people of every genotype can build speed and strength with the right training.

What it means for your training

If you are RR or RX, your fast-twitch fibres are built to respond to heavy lifts, sprints and plyometrics, so power work should pay off quickly. If you are XX, you can still build strength and speed, but your natural advantage is fatigue resistance: higher-rep strength work and longer efforts play to it.

PPARGC1A: the mitochondria gene

Long name: peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α)

What it does: tells your muscles to build more mitochondria, burn fat and carbohydrate for fuel, and shift fibres towards the fatigue-resistant, slow-twitch type. Every long or hard session switches it on.

Sports connection: endurance

Every version responds to training. The gene shapes how strongly you adapt, not whether you can.

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The supporting cast

Eleven more genes add smaller effects. Each one nudges a single system, and each leans towards power, endurance or both.

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How the Stride fitness report reads your DNA

No single gene makes you a sprinter or a marathoner. The signal comes from the combination, and some genes amplify each other: the power-linked version of AGT has a stronger effect alongside ACE’s D version, while the endurance-linked version of BDKRB2 works best alongside ACE’s I version.

Your Stride fitness report analyses 15 variants across these 14 genes, reading ADRB2 at two separate points. Each variant you carry adds weight to the power side, the endurance side or neither. Together, they place you on a spectrum from strongly power to strongly endurance.

The report also covers three more areas that shape how you should train.

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How to train for your result

If you lean power

Build your plan around short, maximal efforts with full recovery. Quality of movement beats volume: stop a set when your speed or form drops.

• Hill sprints and plyometrics

• Kettlebell swings and Olympic lifts

• Heavy compound lifts in sets of three to five reps, with two to three minutes of rest between sets

If you lean endurance

Build your plan around steady, sustained work. Spend most of your training at a pace where you could hold a conversation, and add one or two harder sessions a week.

• Long runs, rides and swims

• Tempo efforts and rowing

• Higher-rep strength work with lighter weights

If you sit in the middle

Mix both, deliberately. A week might include two strength or power sessions, two steady aerobic sessions and one interval session that blends the two.

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What your genes can’t tell you

Each variant here has a small effect on its own, and research on several of them is still developing. Your sleep, nutrition, training history and consistency all shape your results as much as your DNA does.

Use your result to decide where to spend more of your time, not to rule anything out.

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FAQs

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The bottom line