Born or Made? The Science of Genetics vs Training in Ultra Trail Running
“Am I just not built to win?” As a proud middle-of-the-pack ultra trail runner, I’ve often asked myself this question while grinding up a steep mountain trail. I log my miles and do the workouts, yet the podium seems forever out of reach. Meanwhile, a few runners fly by effortlessly, as if born for the mountains. It raises the age-old debate: how much of our running potential is due to training, and how much is inherent in our DNA? In this article, I’ll explore what science says about genetics versus hard work in endurance performance – all from the personal perspective of someone who runs for the love of it, even if my genes won’t make me the next champion.
The Genetic Hand You’re Dealt (Nature’s Contribution)
Trail running might feel spiritual, but there’s some cold, hard biology under the hood. Athletic performance is a complex trait influenced by both genetic and environmental factors. In fact, studies of families and twins estimate that genetic factors account for approximately 40–70% of the differences in key performance traits. In endurance sports, specifically, about 44–68% of performance variation can be attributed to genetics. In other words, the parents you were born to do play a huge role in your running ability.
What are these genetic factors? Researchers have identified hundreds of genetic variants associated with athletic traits. By 2021, over 220 genetic variations had been linked to factors such as endurance capacity, muscle strength, power, and even recovery and injury risk. Each of these genes has a small effect, but together they shape the kind of athlete you are. Here are a few important areas where genetics can give someone an edge:
Muscle Fibre Type: We each have a mix of slow-twitch and fast-twitch muscle fibres. Slow-twitch fibres contract slowly but don’t tire easily, powering steady endurance efforts such as ultramarathons. Fast-twitch fibres fire quickly and explosively, making them ideal for sprinting or steep hill bursts, but they fatigue more quickly. Your fibre composition is largely inherited. Some people are born with a higher proportion of slow-twitch fibres, essentially pre-tuned for endurance, while others are geared toward speed. A famous example is the ACTN3 gene (sometimes dubbed the “sprinter gene”). One variant of ACTN3 (designated R577X) produces a non-functional form of a muscle protein, resulting in fewer fast-twitch fibres and more slow-twitch fibres. Elite endurance athletes are more likely to have this variant (the XX genotype), whereas sprinters and power athletes are more often found to have the version that produces the normal protein (the R allele). This doesn’t mean a single gene makes you an ultrarunner, but it illustrates how genes can tilt you toward endurance or speed from the start.
Aerobic Capacity (VO₂max): This is the maximal rate at which your body can use oxygen during exercise, often considered the engine size of an endurance athlete. VO₂max has a strong genetic component. If you’ve ever met someone who barely trained yet blazed through a 5K, they probably won the genetic lottery on VO₂max. Elite endurance athletes (think Olympic skiers or pro cyclists) can have VO₂max values over 80–90 mL/kg/min, roughly double that of an average person. Studies indicate that genes account for approximately 50% or more of the variation in VO₂ max between individuals. Even more intriguing, how much your VO₂max improves with training – your trainability – is also partly encoded in your DNA. In the HERITAGE Family Study, after a standardised 20-week training program, some people improved their VO₂max by a whopping ~1 litre/min while others saw almost no improvement at all. The researchers found that approximately 47% of the variability in these training responses was genetic. In simple terms, two runners could follow the same training plan – one might make massive gains while the other improves only modestly, due to differences in their genes. If you’ve ever felt like you’re “not a high responder” to training, there may be a genetic truth to that.
Body Size and Morphology: Trail runners come in all shapes, but certain body traits confer advantages. For example, being naturally lean and light can improve your running economy (by carrying less weight uphill). Height and limb proportions can affect stride and climbing ability. These traits, too, are influenced by genetics. Even bone structure matters; a comment often overlooked is that “the way your bones are shaped matters” for running. Our skeletal frame can significantly impact running form efficiency and susceptibility to injury. Of course, body composition can be modified with training and diet, but your baseline build is something you inherit.
Altitude Adaptation: Many ultra trail races take place in the mountains at high altitude, and here genetics can quietly tip the scales. Over generations, populations living in high-altitude regions (like the Himalayas or Andes) have developed genetic adaptations to thin air. For instance, Tibetan highlanders commonly carry a gene variant (EPAS1) that keeps their red blood cell counts lower but more efficient at altitude, thereby protecting them from altitude sickness while still delivering oxygen effectively. Even on shorter timescales, if you were born and raised at altitude, you may perform better in mountain races than someone from sea level. A study on professional cyclists found that racers who grew up above ~1,800m (6,000 ft) maintained a higher power output at elevations above 2,000m compared to those born near sea level. Both groups suffered as the air thinned, but the lowlanders’ performance dropped off much more sharply at altitude. The mountain-born athletes had an edge, likely due to developmental and genetic factors honed by living at high altitudes. In ultra mountain races, this can mean one runner’s lungs and blood are literally better wired for the thin air than another’s.
It’s clear that genetics endow certain advantages, whether it’s bigger aerobic engines, muscle fibres that favour endless uphill grinds, or a body built for efficiency. Elite athletes often benefit from a “talent” component, those lucky genetic cards that set a higher performance ceiling. Many top runners were notably quick even as children, long before they began structured training. (Ask the fastest runner you know how they did in their childhood fitness test mile – chances are, they were always near the top!) This isn’t to say champions don’t work hard – they absolutely do – but it underscores that the playing field in endurance sports is not level at the genetic start.
However, before you resign yourself to slow genes, remember that genetics is only part of the story. If roughly 50% of performance comes from DNA, the other 50% comes from elsewhere. Let’s talk about that other half: training, environment, and the power of human adaptability.
Training, Environment, and the Other Half of the Equation
The good news is that your genes don’t seal your fate, far from it. Environmental factors, including training, nutrition, coaching, lifestyle, and opportunities, account for a significant portion of your athletic development. It’s often said that “hard work beats talent when talent doesn’t work hard.” A less catchy but more accurate mantra might be: “Performance = Consistency + Genetics”. You can’t change your genetic hand, but you can absolutely change how close you get to playing it out entirely.
Think of your genetic potential as a ceiling; most of us are nowhere near that ceiling in practice. Why? Because reaching it would require years of optimised, dedicated training that few non-professionals have the time (or desire) to do. In fact, one coach noted that most of us never come anywhere close to our genetic limits unless we train at an elite level for many years. There might be an Olympic champion somewhere inside you, but unlocking that level of performance could take a decade of monastic training – not exactly feasible if you have a job, family, or, you know, a life! So, for the everyday trail runner, it’s often our training and lifestyle that set a lower ceiling than our genes would, which is a strangely comforting thought. It means with consistent training, we all have the capacity to improve dramatically, often far beyond what we initially think.
Consistency and smart training are the great equalisers. Unlike genetic talent, consistency is accessible to everyone. Logging miles week after week, year after year, leads to steady progress. Improvements in endurance come from cumulative adaptation, including the development of more capillaries in your muscles, denser mitochondria, stronger ligaments, and a more robust heart. These are earned through training. And while two people might not gain equally (one might improve faster due to genetics), both will get substantially better than if they hadn’t trained at all. For example, many first-time marathoners experience significant improvements over the course of a year of training, resulting in a substantial drop in their finishing time. That’s not genetics changing – that’s pure training effect.
Moreover, training itself can interact with genetics in fascinating ways. The burgeoning field of epigenetics reveals that how you live and train can influence which of your genes are active or silent. Essentially, while your DNA code is fixed, your lifestyle can tweak how that code is read. Endurance training might “turn on” specific genes that help you process oxygen or resist fatigue, effectively unlocking latent potential. Some of these changes can even persist for a long time (and there’s preliminary evidence they could be passed to offspring!). So, while you can’t rewrite your DNA, you can change how your body expresses it through consistent training stimulus – literally, training can make you more of an endurance athlete at the molecular level. Think of it as teaching your genes new tricks.
We must also consider the broader environment beyond just workouts. Factors such as nutrition, recovery, psychological support, and coaching knowledge have a profound impact on performance. Two runners with identical genetic talent can end up miles apart if one has an innovative training plan, a nutritious diet, and a healthy environment, while the other overtrains, underfuels, and gets injured. Access to trails, training facilities, or living at altitude can all confer advantages that have nothing to do with innate talent. Even the age at which you start matters – someone who began endurance training at a young age likely built a higher base fitness (and possibly a higher capillary density or efficiency) than someone who started in their 30s. As one trail runner pointed out, the age at which we start and access to resources can create an “aerobic privilege” that isn’t purely genetic. For example, if you ran cross-country since childhood (and accumulated thousands of hours on your feet), you’re going to have a leg up on a person who discovered running as an adult, even if you had similar DNA.
This raises a key point: we often compare ourselves to others without realising that we might not be on a level playing field in terms of experience or circumstance. Social media and race results provide us with raw numbers (pace, finish times), but no context about the person’s background. Next time you find yourself lamenting, “Why can’t I run as fast as X?” remember that X may have had 10 more years of base training, or a coach guiding them, or simply more time to train each week. Comparison without context is the thief of joy (and often misleading).
One-Size-Fits-All? Not So Fast
A practical takeaway from the nature-nurture mix is that training plans should be personalised. There is no one-size-fits-all approach, despite what worked for your favourite elite runner. Exercise geneticists emphasise tailoring training to individual differences in genes, environment, and lifestyle. If you’ve ever tried an elite’s training schedule only to end up injured or burnt out, you’ve felt this first-hand. Elites might handle 160 km weeks thanks to a mix of genetics (e.g., resilient connective tissues, efficient recovery systems) and years of gradual build-up. If you or I jump to that volume, we might break down. So, while it’s great to learn from the best, be ready to tweak advice to fit your own capabilities. Science is moving toward “precision exercise”, the idea that we can optimise training by understanding an individual’s unique makeup. Until you get your genome sequenced and an AI coach (one day, perhaps!), the best approach is to listen to your body, pay attention to how you respond to workouts: some runners thrive on high mileage, others on quality intervals; some need more rest days; some respond well to cross-training. These differences might have genetic roots (for example, a gene affecting collagen might make one runner more injury-prone, so they require more rest); however, regardless of the cause, the solution remains the same: personalise and progress gradually.
One comforting thought from Coach David Roche: don’t obsess too much over your genetic limits. He suggests that there’s little point in getting tested for VO₂ max or genetic potential unless you plan to train to the maximum; otherwise, the data might confuse your thinking. Instead, focus on the controllables: consistent training, smart recovery, nutrition, and making running enjoyable so you stick with it for years. You’ll likely surprise yourself with how far you can go, genes aside. After all, most of us have a lot of untapped potential waiting for the right training stimulus.
Mind Over Matter: The Mental Factor in Ultras
Physical talent and training are crucial – but in ultra-distance trail running, there’s a third ingredient that often comes into play: mental toughness. Ultramarathons test the limits of human endurance not just in muscles and lungs, but in willpower. Here’s where I (and many non-elite ultrarunners) take solace: sometimes having a stubborn, gritty mindset can be our “secret weapon” when the going gets tough. I may not have elite genetics, but I do have a well-honed stubborn streak that has dragged me through many 50K+ finishes!
Science acknowledges this mental dimension. Research on ultra-marathoners has found that they tend to have higher levels of mental toughness compared to athletes in many other sports. The ability to suffer through pain, to endure hours of fatigue and keep moving, and to resist the urge to quit when your body is screaming at you, these are hallmarks of the ultrarunning psyche. In ultras, the mind can be as important as the body. In fact, simply having the confidence and will to attempt an ultra is a form of psychological filtering; it has been suggested that there’s a “threshold” level of mental toughness required to train for and start an ultra. Those who lack it are unlikely to make it to the start line. So if you’re routinely grinding through 6-hour training runs in the rain, congratulate yourself – you likely already have a strong mental game.
However, mind over matter will only take you so far. A recent study of elite ultra runners (100-mile trail race finishers) found that within that highly tough group, differences in mental toughness did not predict who ran faster. In other words, once you have established that baseline toughness to compete, winning comes down to various factors, such as physical conditioning, nutrition strategy, efficient pacing, and perhaps raw talent. This resonates with my experience: mental grit can get you to the finish of an ultra no matter how long it takes, but it probably won’t put you on the podium unless your legs, lungs, and training are also up to speed. Both the brain and body matter; you need the resilience to endure and the fitness to perform.
Interestingly, there’s even a nature vs nurture debate in psychology. Some argue that people may be born with a higher tolerance for pain or a more resilient personality, while others believe these traits are developed through life experiences. It’s likely both: your genes influence baseline temperament (for example, there are genetic links to risk-taking and how the brain processes dopamine, which could affect one’s drive to push limits), but ultra training itself can forge mental toughness. Every gruelling run builds your confidence that you can suffer and not break. In my case, I know my years of slogging through long runs have raised my pain threshold and perseverance far beyond what my 20-year-old self (back when I hadn’t yet run anything over 10K) would have tolerated. So, even here, training and mindset interact with whatever innate stubbornness you had to begin with.
The mental side also ties back to enjoyment and motivation. We, non-elite runners, often run ultras not for prize money or accolades, but for personal fulfilment – the adventure, the scenery, the community, and the joy of discovering our own limits. That passion can be a powerful motivator, arguably a “genetic” trait in itself (some of us are just wired to love Type-2 fun!). And motivation is crucial: it keeps you training consistently and pushes you through dark moments in a race.
Bottom line for the mental game: if you have a naturally strong will, it’s a gift in ultras – nurture it. If you don’t think you’re especially tough mentally, don’t despair; you can train your mind like a muscle by gradually doing harder things, practising positive self-talk, and learning from each tough run. Just as not everyone is born with an 85 mL/kg VO₂max, not everyone is born an iron-willed ultra warrior, but you can become much tougher through practice. In my experience, finishing ultras has built confidence that spills into other areas of life – a reward far more valuable than a podium spot.
Embracing Your Own Trail (Conclusion)
After diving into the science, where does this leave those of us firmly in the middle of the pack? For me, it’s actually empowering. Yes, genetics are real – some runners will always have it easier when it comes to speed and endurance. Not everyone can win a UTMB or set an FKT, and that’s okay. Your body may not be built to sustain a 6-minute mile over mountain passes, especially if you (like me) aren’t the lean, high-VO₂max prototype. Acknowledging these differences is healthy. As one trail running writer put it, “so much of our abilities – running, climbing, skiing – are out of our control (genetics, how young we got started, access to resources)”. In other words, if you’re slower than someone, it might just be because of factors you never had a say in – so don’t beat yourself up. And conversely, if you’re faster than others, stay humble, because luck probably played a role in that.
At the same time, focusing solely on genes would miss the bigger picture. What’s in your control is how you train, how smart you are about recovery, and how you mentally approach challenges. These aspects can take you much further than you might imagine. You may not have the DNA of a champion, but you can absolutely be the best version of you as a runner. And the best version of you might astonish the current you! The improvements you achieve through training and perseverance are very real and meaningful. There is genuine satisfaction in seeing your own progress – running a first 50K, setting a PR, or just feeling stronger on your favourite climb than you did last season. These victories belong entirely to you and don’t depend on having Olympic parents or a particular gene variant.
Most importantly, remember why we run. Elite or not, trail running gives all of us the same gifts: the crunch of dirt underfoot, sunrise over foggy peaks, the camaraderie of shared miles, and the profound sense of accomplishment (and relief) after pushing through a hard effort. Those experiences are not genetic – they’re human. In our trail community, a person’s worth is not measured by their finish time. We celebrate effort, adventure, and love for the sport. As one runner wisely noted, please don’t ever apologise for being slower, because chances are it’s due to factors like genetics or simply being new to the sport. Your pace doesn’t define your value.
In the end, I’ve made peace with the fact that I’ll likely never win a race – my physiology just isn’t that of a pro. But that doesn’t diminish my passion one bit. I still push my limits – my limits – and that journey is incredibly rewarding. Knowing the science has only reinforced my enjoyment: I marvel at how adaptable the body is (I can improve with training!), and I also smile at the genetic quirks that make each of us unique on the trails. So if you’ve ever doubted yourself for not being naturally “fast,” take heart. Yes, some of it is in your genes. No, you can’t change that. But you can train, you can get better, and you can embrace the runner that you are.
Keep running, keep grinding, and keep exploring. The mountains don’t care about your VO₂ max or how many fast-twitch fibres you have – they welcome anyone willing to put one foot in front of the other. And that, ultimately, is why we trail run: not to win some genetic lottery, but to experience the thrill of the trail. In a sport where effort and passion mean as much as talent, there’s a place for every one of us, from the front of the pack to the back. Enjoy the run!
Sources:
MedlinePlus Genetics – Is athletic performance determined by genetics?
Frontiers in Genetics (2023) – Heritability of athletic performance ~50%; endurance traits 44–68% , elite status ~66% genetic
BMC Genomics – HERITAGE Family Study on VO₂max trainability (47% genetic)
Trail Runner Magazine – Performance = Consistency + Genetics (David Roche, 2016)
ClimberKyle Blog – Why Trail Runners All Believe They are “Middle of the Pack” (Kyle, 2023)
Science X / PLOS ONE – Study on mental toughness in ultra runners (Brace et al. 2020)
Outside Magazine – To Win in the Mountains, It Helps to Be Born There (Alex Hutchinson, 2022)
Wikipedia – VO₂ max reference values (elite >90 mL/kg/min)