Nature versus nurture: Pro cyclists are born, but also made

In the peloton at this year’s Vuelta a España are brothers Gorka and Ion Izagirre and Jesús and José Herrada, cousins Dan Martin and Nicholas Roche, and twins Adam and Simon Yates.

These riders are but a few names on the extensively long list of families that have populated the pro peloton over the years. Who can forget Andy and Fränk Schleck and the “Schleck Sandwich” of the 2011 Tour de France, an alimentary metaphor aptly used to describe how Cadel Evans found himself wedged for several stages between the two talented brothers in the general classification. Andy and Fränk’s father Johnny was himself a super-domestique who rode the Tour eight times, and his father Gustav was also a professional cyclist in the 1930s.

Then there were the French Simon brothers – all four of them – whose string of successive participations at the Tour de France resulted in their family being represented in every single edition of the race, except for just one, from 1980 to 2001.

In the 2018 men’s WorldTour, at least 18 riders are brothers and four are cousins, and that’s not including this year’s Pro Continetal and Continental lineups, or even the women’s peloton, where there are several more relations to be found.

So how much of the precocious familial talent in the peloton can be put down to genetics, and how much is cultivated by environmental influences? In other words, to what extent is a pro cyclist born, rather than made?

Irish cousins Dan Martin and Nicolas Roche at the opening ceremony of the 2014 Giro d’Italia. Martin is the son of Neil Martin, a former British professional, and Maria Martin, sister of 1987 Triple Crown winner Stephen Roche, who is father to Nicolas Roche.

The Role of Genetics in Sport

Since the Human Genome Project reached completion 15 years ago, researchers have sought to pinpoint specific genes and genetic variations that contribute to athleticism.

After examining almost 800 sets of twins, researchers concluded that over 65% of variation in athletic ability comes down to genetic factors. Other studies have found this percentage to be significantly higher, suggesting that genes alone contribute more to sporting success than training, nutrition, coaching, tactics and any other interventions combined.

This nexus between performance and heritability would seem to imply that the making of a race-winning pro cyclist is more akin to a game of roulette than a carefully executable game of chess.

It’s been hypothesised that genetics has greater scope to influence performance in sports that lie at the polar extremes of the athletic spectrum, such as marathon running or sprinting. Road cycling is a sport that is characterised by extreme physical demands, be it climbing up inexorably lengthy, lactic acid-churning gradients, or bursting across the finish line at speeds of over 65km/h in a chaotic bunch sprint.

We know that pro cyclists generally possess a high maximum oxygen uptake (80ml/kg/min VO2 max), high power-to-weight ratio (6-7W/kg at VO2 max, and over 20W/kg in sprints), high peak-power output (over 1500W), and a high anaerobic threshold, coupled with low rates of body fat (5-10%) and larger hearts and arteries. Although some of these important traits may be susceptible to improvement through training, most are highly heritable characteristics, meaning that they are significantly determined by biochemistry.

A recent twin and family study found that around half of the differences observed in performance-related attributes like these can be put down to genetics. Going further into cycling specifics, research suggests that aerobic fitness (VO2 max) is about 50% heritable, the combination of slow-twitch (endurance) and fast-twitch (sprinting) muscle fibres is about 45% heritable, and strength and muscle mass is more than 50% heritable.

By contrast, other sports such as gymnastics or diving rely more on attributes like agility, balance and accuracy, traits that are less influenced by genetics and more prone to improvement with training and practice.

Athleticism in cycling would therefore appear to be a highly biologically-dependent phenomenon. At least to the pro cyclist, genetics is a significant determinant of performance.

Mathieu van der Poel (left) has been more successful than his older brother, David (right), however both share genes inherited from their father, former professional Adrie van der Poel, as well as their maternal grandfather, French cycling legend Raymond Poulidor.

Sprinter or Climber? It’s in the Genotype

Let’s take a look at the genetics that regulate skeletal muscle fibre type, a crucial element in the physiology of pro cycling.

The key force that cyclists use to push the pedals is derived from skeletal muscles, of which there are two types: slow-twitch fibre muscles and fast-twitch fibre muscles. (The term “skeletal” in describing muscle types refers to their attachment to bone, via tendons, as opposed to involuntary muscle types that control internal organs, and the heart.)

Slow-twitch fibres contract slowly, can be put to use for longer periods, and are ideal for endurance activities. Fast-twitch fibres, on the other hand, contract quickly and produce greater speed and strength, yet tire faster, and are so suited to more rapid and forceful activities such as sprinting.

Studies performed on dizygous (non-identical) and monozygous (identical) twins demonstrate that an individual’s muscle fibre composition is predominantly influenced by genes.

One of those genes may very well be the ACTN3 gene, which has been dubbed “the sprint gene.”

ACTN3 encodes the production of the protein alpha-actinin-3, which forms part of the contractile mechanism found within fast-twitch fibre muscles, those that are required to generate explosive sprinting power. However, researchers have also identified a variant of this gene (the X variant) which leads to an abnormally short alpha-actinin-3 protein that is rapidly broken down.

So we know that there are two variants of the gene, R (the functional variant), and X (the lesser functional variant). Every individual receives one allele (either R or X) from each parent. As a result, there are three possible genotype combinations: XX, RR and RX.

In individuals with the XX variant, the production of the quick movement protein is, predictably, significantly blocked. This leads to a reduction in the proportion of fast-twitch muscle fibres and an increase in the relative amount of slow-twitch fibres. Studies have shown that the XX genotype is far more common among endurance athletes than in the general population.

The RR genotype, on the other hand, is more prevalent among athletes who rely on strength and speed to excel, in other words, the sprinters. In fact, studies examining the DNA of past and present sprint world record holders failed to identify even one single athlete who carries the XX genotype, despite the fact that 20% of the general population possesses this variant.

This could go some way to partly explaining why all three van Poppels are sprinters, both Zabels are sprinters, and all three Schlecks are more partial to climbing than dishing it out amongst the fastmen. And while it is by no means a hard-and-fast-rule that family members will all race alike, muscle fibre type is a highly heritable characteristic, and the below graph says much about the impact that this can have on athletic performance, particularly in cycling.

Data obtained from D. MacArthur and K. North, “ACTN3: A Genetic Influence on Muscle Function and Athletic Performance,” 2007.

The Hidden Effect of Genetics: Training

If you think that one can invariably circumvent the role of genetics in cycling through sheer hard work, then think again. Genetics reaches deep into the minutiae of many determinants of athletic performance, even those that we think lie beyond its grasp or fall under the ambit of human volition and pure willpower.

Training is one of those areas. You’d think that a fervent adherent to the aphorism “the more I practice, the luckier I get” would eventually succeed in tipping the scales away from genetics in favour of good old-fashioned hard work. Think again.

Some cyclists, no matter how much they practice, will never become as “lucky,” in this sense, as their competitors or teammates. Responsiveness to training is, it turns out, once again mediated by genes.

Canadian studies into trainability found that when inactive test subjects underwent exactly the same training regime for just over four months, twins produced identical rates of improvement in aerobic capacity, compared to the wild fluctuations observed in the control group. The researchers concluded that the extent to which athletic determinants such as aerobic efficiency can be improved through training is 50% reliant on the absence or presence of specific genes.

The fact that some cyclists may respond more effectively to practice and training than others, even those with a “natural” athletic predisposition, may go some way to explaining why certain young talents in the peloton never seem to reach their full potential. Perhaps some failed cycling prospects have been unduly labeled as lazy, distracted, or uncommitted, when in fact their genes have imposed a ceiling or damper on their ability to develop at the same rate as their peers in response to training.

Video: UCI feature on British sisters Hannah and Alice Barnes

Nurture, and Marginal Gains

When the renowned physiologist Per-Olof Åstrand was asked to single out the best way to improve sporting performance, he replied succinctly, “choose your parents carefully.” The implication: Elite athletes are born and not made, and that practice, training and all other exogenous interventions ultimately play only a nominal role in athletic success.

So are we inexorably bound up in the seemingly ubiquitous grasp of genetic determinism, as Åstrand seems to suggest?

While one’s genetic makeup does provide a rigid base upon which to build, it is still only that — a base. Environmental factors are unquestionably an important factor in sporting success, particularly in the modern era of marginal gains. They have a critical potential to influence how genetic characteristics come to be expressed in an athlete as phenotypes — observable physical features that stem from the synergy between a person’s genotype and external environment.

Good cycling genes alone won’t cut it. Genetically-mediated lack of responsiveness to training aside, we’ve all seen young riders who were touted as potential stars fall prey to unsavoury lifestyle choices and drop precipitously off the radar into the murky shadows of a disappointingly lacklustre career. Genes alone do not provide a straightforward pathway to the podium, despite the likes of habitual party animals in the peloton, such as Mario Cipollini, Frank Vandenbroucke and the younger Tom Boonen, at times leading us to believe that by virtue of their sheer talent on the bike, single-minded dedication wasn’t a particularly important factor in their sporting prowess.

This is where training, coaching, tactics, equipment and psychology all come into the equation of success. Performance is influenced by a broad range of exogenous factors, including support from family members and coaches, economic circumstances, sports science and nutrition, and sometimes also luck. Pro riders are surrounded by an ever-increasing entourage of niche experts, perhaps nowhere more evident than at Team Sky.

The British outfit seems to have the ability to make a super-domestique out of riders who had never previously demonstrated such superlative climbing abilities. And when they leave the team, many somehow never manage to return to the same level. Sky does admittedly have the budget to buy riders who are already amongst the best in the peloton, and the riders who they contract are undisputable talents, yet the team somehow manages to make them even better.

Few sports rely as heavily on an extremely fine balance of training, psychology, nutrition, tactics, coaching, equipment, and physiology as pro cycling, and Team Sky capitalises on this multitude of intersecting performance variables. A read through the files that the team released after this year’s Giro d’Italia (which detailed Chris Froome’s pre- and post-stage weight and journaled the nutritional value of everything he consumed, down to the last gram of Haribo) demonstrates how the team accounts for even the most miniscule variables and subjects them to rigorous scrutiny and control.

Colombian Sergio Henao (left) and his cousin Sebastian Henao (right) both ride for Team Sky.

This is the true utility of marginal gains. Pursuant to this philosophy, Team Sky seems to be attempting to skew the interaction between the dual forces of nature and nurture, to tame the genetic roulette of pro cycling and transform it into a manipulable game of strategy. And it seems to be working.

But can grit, and indeed marginal gains, ever count for more than genetics?

Perhaps ask Muggsy Bogues, the 5-foot-3 NBA point guard of the 1980s and 1990s, or the 5-foot-9 slam-dunk star Nate Robinson.

The fascinating example of Dan McLaughlin, a 30-year-old photographer who quit his job to take up golfing under the premise that mastery in a given field requires 10,000 hours of practice — made popular by Malcolm Gladwell’s Outliers: The Story of Success —  puts this very question to the test.

For years, McLaughlin spent several hours every day honing his skills on the golf course, and at the halfway point he’d reduced his handicap to 2.6, a level achieved by less than 6% of golfers. Unfortunately, plagued by back injuries, the aspiring pro golfer eventually hung up the clubs in resignation after more than 6,000 hours of practice. Despite pushing himself to the limit, he came up short.

Yet what the project also demonstrated was the vast number of variables, extending far beyond deliberate practice, that are required to achieve mastery in a particular sport. Professional instruction, a workable support network, and optimal psychological motivation were all vital aspects that he found lacking. 10,000 hours of practice or not, bringing about an environment that is conducive to success is vital, but it’s not as easy as it sounds.

Brothers Nairo and Dayer Quintana at the start line of the 2017 Milano-Torino.

The mental edge

While it’s not possible, at least for the moment, to safely and reliably manipulate genes to enhance athletic performance, individuals can nevertheless strive to make the most out of the DNA that their parents have passed down to them.

Motivation, for example, is known to be a key factor in sporting success. So can particular personality traits make a key difference in sports, with other conditions remaining the same?

Scientists in Italy set out to answer this very question. They studied identical twins who had both competed at the Olympic level in the 20km walking discipline. The pair had trained together for more than 15 years and followed precisely the same regime, yet one twin enjoyed much more success than the other. Upon examination, their physical capabilities were found to be identical. The only area in which they differed was personality. The more successful twin demonstrated a marked tendency to refrain from acting upon his negative emotions, whereas his brother was appreciably above average in his tendency towards venting his frustrations.

The researchers concluded that these characterological differences contributed to the discrepancy in the twins’ levels of competitiveness, and extrapolated to suggest that variations in personal traits such as confidence, anger-channelling ability, and motivation could explain differences between sporting twins. This may not necessarily contribute a great deal to performance, but at the elite level, it could mean the difference between standing atop the podium or heading straight back to the team bus after a race.

Twin brothers Simon and Adam Yates, at the 2017 Vuelta a España

Cycling success is a bio-cultural phenomenon

All other things equal, hard work can bring incredibly rich returns. But in the real world, no athlete is a tabula rasa. Professional coaching and training may contribute to greater success, but genetics determines an athlete’s ability to reach that privileged point in the first place.

Environmental intervention can pay dividends, to a point. The debate at the core of the nature vs. nurture debate: Where does that point lie? The ceiling of achievement would appear to be higher for the naturally gifted. One way to conceptualise this is to consider an individual’s base and peak sporting performance potential as biologically determined parameters within which environmental interventions may exert some influence.

A cyclist (Rider A) who is more naturally talented than his competitor (Rider B) will not necessarily always, or indeed ever, outride him. If Rider B trains under optimal conditions, but Rider A rider relies solely on his favourable genetics, the significance of their biological differences is negated. Inheritability of sporting prowess doesn’t necessarily translate into inevitability of superior results. Hard work can beat talent if talent doesn’t work hard.

Professional cyclists are both born and made. Favourable genetic variations may have provided these lucky individuals with potential, but they have had to unlock that potential with appropriate training in an environment that is conducive to success.

Notching up an impressive palmarès requires the synergy of physiological, behavioural, and environmental variables. All are necessary, and none alone are sufficient. Practice itself will not land you on the podium. Neither will genetics. Neither will pure luck. To stand on the podium, a rider is going to need all three.

About the Author

Stephanie Constand works as a press officer for BORA-hansgrohe, and also provides PR work for other pro cycling teams and race organisers. Having originally worked in academia and as a lawyer, with a special interest in sports law and economics, she has written for a range of online and print magazines and is currently working on a book. She can be found on Twitter at @stephconstand as well as at her web site,

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