The Nature-Nurture Debate in Sports: Are Athletes Born or Built?
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What does it take to be a great athlete? Some say that “DNA is destiny” or “it’s all in the genes.”
Other people will vehemently answer this question with “it just takes a big heart” (figuratively, not literally) or “hard work, just good old-fashioned hard work.” This latter response falls in line with the thinking of the “10,000 hour rule”—which was misconstrued in Malcom Gladwell’s book Outliers. This thinking also aligns with Daniel Coyle’s book The Talent Code about how greatness isn’t born, it’s a matter of how it’s nurtured.
This, of course, brings us to the age-old nature-nurture debate. Despite articles and opinions on both sides, I’m here to tell you that it is not a debate—because athleticism requires both nature and nurture.
We tend to think of things as black or white, but often it’s really a shade of grey.
I cannot tell you how often I’ve had this conversation and debate...well, if you’re really asking, it was actually 43 minutes ago with someone who told me that mental health issues are (100%) GENETIC! I’ve given an entire lecture on this topic to undergraduate Kinesiology students, and it comes down to the following equation, which determines the shade of grey:
Phenotype = Genotype + Environment + GxE interactions and GxG interactions
The phenotypic expression of a human trait (from eye color to height to muscular strength to disease risk, etc.) is COMPLEX and most often (99.998%) involves nature and nurture.
What Role Does Genetics Play in Athleticism?
There should be no denying that genetics play a role in sports. Let’s start with body size. “He’s built like his dad.” Or “he’s going to be a big kid. Have you seen his parents?” And indeed, height in particular has a strong genetic component.
And then there is the more sweeping statement, “her mom (dad/brother/sister) was a great athlete.”
These observations are actually an approach taken by researchers to examine the contribution of genetics to athletic traits, using twin studies and family studies. In one of the first studies of twins, it was shown that the intrapair correlation (Twin A-Twin B) was higher in identical twins (0.91) compared to dizygotic or fraternal twins (0.44) for maximal aerobic fitness level. Note how close the values on the graph are in the identical twins compared to the fraternal twins. This indicates a closer resemblance in aerobic fitness in the twin pairs who share the same DNA. Several other twin and family studies have replicated these findings and extended to several other physiological traits, like strength, power, etc. Overall, the estimated heritability generally falls within 25-60%.
With modern advancements in molecular biology and the sequencing of the human genome, specific DNA sequences and what have been referred to as candidate genes have been associated with specific traits. A list of these SNPs and candidate genes related to human fitness phenotypes is available here.
Genes known to affect athleticism and fitness on chromosomes 7 – 12. Taken from Bray et al. The human gene map for performance and health-related fitness phenotypes: the 2006-2007 update. Medicine and Science in Sports and Exercise, 41(1), 35-73, 2009.
But let’s remember that, in terms of the genetics, there are only a few single gene traits or diseases. (And don't even get me going on epigenetic mechanisms!) Furthermore, all of the athletic capacities or fitness phenotypes are influenced by hundreds of genes—they are what is called “polygenic.” And to make things more complex, these genes interact with each other (GxG interactions).
Direct-to-Consumer Kits: Caveat Emptor
This technology and science of human genetics has also prompted the commercialization of direct-to-consumer genetic testing for the purpose of sports. You know, swab your cheek, mail it in, and they’ll tell you if you or your kid is going to be an athlete. Or, if you should be an endurance or power athlete.
Caveat emptor. Buyer beware! It should be clearly understood that two position statements published in the British Journal of Sports Medicine have denounced the usefulness of genetic testing for the purposes of talent identification and sports performance.
Genetics and the Training Response
Until this point, only the association of genes with sports performance has been discussed. However, genes do not act as free agents. What does this mean? Basically, the ability of a gene to influence a specific trait can be enhanced or inhibited by interactions with the environment (GxE interaction). The environment of interest to us is the training environment. Yeah, the human organism is indeed a freakin’ complex machine!
Now, there are several studies that have shown that if exposed to an adequate training stimulus, there is an improvement in fitness. For example, you have seen several times that if you train an individual or a team that there is on average a 10-20% improvement in strength or conditioning level after 6-8 weeks. However, some individuals improve more than others despite being on the same training program.
Do you think genetics has anything to do with the variation in training response?
Let’s go back to our twin studies. In one of the first studies of its kind, 10 pairs of identical twins went through a 20-week endurance training program 4-5 times per week, 40 minutes per session, at an average intensity of 80% of the maximal heart rate reserve. The group average training effect on maximal aerobic fitness was 12%; however, the range went from 0% to 41%. Indeed, we have responders and non-responders. And we also have quick responders and slow responders. And, members of the same twin-pair yielded approximately the same response to training indicating a genetic basis to the training response.
How Does This Relate to LTAD?
Recently, I spoke at the 2019 Child to Champion conference on the topic of talent identification. I presented some of the above information and came to the following conclusions:
It is important to understand that what you see on the playing field and in the weight room are Phenotypes, or the manifestation of a trait resulting from the expression of relevant genes and non-genetic influences and their interactions. Furthermore, how young athletes respond to a training program can vary due to genetics. The human body is complex— respect it!
There is also the need to consider the impact of normal growth and maturation on both the genetic and environmental factors of sports performance.
Although there is scientific evidence for a genetic basis to athleticism and the trainability of physical qualities, direct-to-consumer genetic testing in relation to sports performance is strongly discouraged. And genetic testing should not be used as a method of talent identification nor to include or exclude athletes from a high-performance program.
So what should we do? In the words of Professor Bob Malina, my PhD mentor and a pioneer in youth sports, “wait and see.” So, although we can acknowledge the contributions of genetics to sports performance, let’s continue to develop the toolbox of athleticism and keep as many in the pipeline for as long as possible and provide them quality coaching because talent—and its development—is dynamic, multidimensional, and COMPLEX!
“Genetics loads the gun but the environment pulls the trigger.”
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