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Having watched a lot of olympians the last few weeks, I was struck by how many of them have actually spent their wholes lives/careers training for their one event (be in running a marathon, or throwing a javelin). This is of course unsurprising - a lot of people take their sport very seriously - but I wondered to what degree these athletes are predisposed to becoming atheletes, and to what degree they just 'happened' to end up doing it.

I've had a bit of a search around, but have been unable to find any studies (although there is an awful lot of media attention to the topic) that actually study the interaction between nature (genetics) and nurture (environment/training etc) in the context of top-end athletes.

It is quite clear to me that the answer is of course 'both', but to what degree? Have any common genetic variants/loci been identified, or is 'athleticism' a far too complex trait for this? Thanks.

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All I can think of is abcnews.go.com/Health/MedicineCuttingEdge/… –  LanceLafontaine Aug 14 '12 at 11:08
@LanceLafontaine That is very interesting - I've seen the mutant animals before, but did not know there were naturally occurring variants in humans! These individuals would certainly be predisposed to become strong-men! –  Luke Aug 14 '12 at 13:00
I'm wondering if there are currently or going to be Olympic "policies" against people like that. It's gives an unfair advantage (that's for sure), but it's not like it's anyone's fault. –  LanceLafontaine Aug 14 '12 at 13:09
@LanceLafontaine you have to remember there will be a gaussian distribution, and these people are just at the very tail of it. I imagine that most athletes will also be close to it, but with a not so pronounced phenotype? At what point labeling these 'extremes' as 'mutants' becomes acceptable, and deem them unsuitable to compete in sports is an interesting thought –  Luke Aug 14 '12 at 13:13
All these fantastic atheletes on the record breaking levels are a combination of hard work, good funding and a good genetic predisposition. Swimmers have flexible joints, Lance Armstrong has an extra large heart. You can train to increase fast twitch muscles and reaction times, but a few extra mutations in your favor makes the champion I think. Horses have been bred to champions for centuries. Human champions also need a genetic advantage. This is just my opinion, but not so controversial in my opinion. –  shigeta Aug 17 '12 at 17:57

3 Answers 3

up vote 4 down vote accepted

For all types of athlete, their ability is determined by both genetic and environmental factors (nature and nurture). The degree to which each contributes ultimately depends on the demands of the sport.

As an example let's compare basketball and golf.

Basketball is likely to have a strong genetic component because players tend to be exceptionally tall (average is over 2 metres and there are only a handful who have played NBA under 1.75m). Because height is strongly genetically (but not entirely) determined by the genes, they have a big influence on whether someone can poses the physical qualities to play in the NBA. However, a large part of their technical capabilities are due to their environment. If you give a basketball to someone who has played 2 games a week their entire lives and ask them to take 10 shots it is likely they would score more than someone who has never seen a basketball!

Comparing basketball to golf, there are all sorts of body types within the PGA tour, and they is no/few obvious genetic traits which golfers tend to have over other people. This would suggest that golfing ability is more affected by environment.

So an easy way to get a rudimentary test of genetic contributions to sporting ability would be to compare frequency distributions of focal traits in the athletes to distributions of regular people. Obviously the phenotypic trait you measure has both genetic and environmental contributions (e.g. childhood diet) which could affect them but it would be a good starting indicator which could give some candidate traits to test.

As a scientist I would also consider sequencing some athletes and some non athletes and seeing which genes the athletes have more often then the regular person's genome. However, such studies are likely to be complex - linking phenotypes (in polygenic traits) to the single allele variants relies on large sample sizes. Generally it will be more difficult if:

  1. There is large variance in the trait
  2. The gene has a small effect (see major and minor effect genes)

Both of these problems going to be positively correlated with the number of genes affecting a trait (how polygenic is it?) which for athletic ability is probably quite a substantial amount of genes.

EDIT: Here are some possible studies for your further exploration of the topic-

Candidate genes for Specific Genetic Markers of Endurance Performance and o2max

Rowers have an excess of the ACE I allele

Elite Italian footballers with "explosive" leg strength also reveal ACE and other genetic markers

A precautionary tale about Genetic tests for athletic ability

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I am thinking that another good example could be 'sumo wrestlers', who are also very different in body types to the average population. –  719016 Nov 9 '12 at 13:00
here is a paper which finds a candidate gene for physical athletic superiority (springerlink.com/content/hwllqyy12x29tpde) in a method similar to that which I suggested. However, I can't find anything suggesting a gene leading people to being predisposed to being an athlete psychologically. The genetics of behavioural psychology is incredibly complex and hotly debated, classic example being "the gay gene." –  rg255 Nov 12 '12 at 10:49
@Luke, does this answer your question? –  rg255 Nov 14 '12 at 10:44
Hi @rg255 - thanks for the information and your opinions, but I was hoping for links to studies (like the one in your comment) where authors have tested for genetic contributions. I am of course expecting a large environmental contribution, but as you suggest the genetic contributions may be sport specific (e.g. height-increasing alleles for basketballers, bulk-increasing alleles for sumo-wrestling... etc). When I have some time later I will follow-up the paper you have sent, as this is quite an old study and have been cited almost 200 times! Clearly some other studies too. Many thanks. –  Luke Dec 12 '12 at 10:18
@Luke there you go (see edit to answer) hopefully these will give you some help - looks like there are a few alleles that regularly come up in these studies (e.g. ACE I). Sorry it took a while to get around to it! –  rg255 Feb 5 '13 at 8:28

Two hints:

  1. Do a google search for the ACTN3 gene (alpha-actinin-3)

  2. Go to the fitness.stackexchange.com site and search for "fast twitch" muscles, for example. There you'll find many similar questions answered.

You can get an answer for you personally by genetic testing.

This is a quote from a genetic testing site 23andme.com (sorry it's behind a paywall). Note there are other companies who can do this equally well.

Genes vs. Environment

Athletic performance has different estimates of heritability, depending on what aspect one examines. For example, differences in the relative proportion of fast-twitch and slow-twitch muscle fiber are thought to have a heritability of about 45%. Although it is not yet clear whether ACTN3 genotype affects this proportion, it has been shown that the SNP in ACTN3 that we report accounts for about 2.3% of the variation in sprinting performance. However, at the molecular level, whether you have 0, 1, or 2 working copies of alpha-actinin-3 is highly heritable. Lastly, muscle fiber only contributes a small part to your overall athletic performance. Other physical characteristics, such as lung capacity, and behaviors, such as regular exercise, also make important contributions to your prowess in sports.

This is considered "established research for 1 reported marker". It is still subject of much ongoing research, though.

So there you have it: around 2% of a difference in sprinting performance. For the general population this won't matter much. But for prospective professional athletes these 2.3% might matter a lot for developing the full potential of their athletic performance (assuming all other environmental factors, are of equal top quality, e.g. technical equipment, coaching efficiency, etc)

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ncbi.nlm.nih.gov/pmc/articles/PMC3255226 - talking about genetic tests like the one for ACTN3 "this is a gross over-simplification of the science, according to many critics of these types of consumer genetic tests, including Timothy Caulfield, a Canada Research Chair in Health Law and Technology. “There are so many factors that contribute to something as complex as performance in sports that it seems ridiculous to narrow it down to this one type of genetic test,” he says." –  rg255 Feb 6 '13 at 8:42
so I'd suggest we can't call it a comprehensive test - individual loci only have minor effects on the overall ability. –  rg255 Feb 6 '13 at 8:50
@rg255: What the law school professor said is "I don't like questions like this narrowed down to 1 genetic test". That may be righteous, but I'm not narrowing it down. The original question asked for a quantitative estimation. Hence, the quote in my answer: we are talking about 2.3% differences here (which won't matter much for the general population) and the quote also says there are many factors. –  knb Feb 6 '13 at 8:58
I just don't think we can call it a comprehensive test –  rg255 Feb 6 '13 at 8:59
i removed the "comprehensive" word. –  knb Feb 6 '13 at 9:05

I don't think this will ever be answered, mostly because studying the long-term effects of athletic training is very difficult. People constantly change their training methods, habits, and schedule, so controls are nearly impossible to construct.

My opinion, is that the nurture component is the strongest, because of the amazing plasticity of the body in response to stress: bones grow/reform differently, neural networks become trained, muscles change. Over many years these can be enormous. This is true of all humans, absent those with severe genetic faults.

Genetics probably has a stronger influence on the psychological traits which might induce someone to train so hard. Though parenting could certainly override this.

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It is difficult but not impossible to quantify. Could you give us some solid scientific references? –  Memming Nov 12 '12 at 15:09
I have no references because I don't think these data exist. Certainly you can get quantitative data, but it doesn't mean that it will be useful. My main point is that there are too many ill-defined variables that need to be tracked for many years. This is nearly impossible to do. –  TonyH Nov 12 '12 at 18:24

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