Is there a genetic holy grail for athletes?

020_ALEJANDRO LUCIAAlejandro Lucia is Professor of Physiology at the European University of Madrid. He has a particular research interest in endurance sport and exercise physiology

Carl Foster_crop

Carl Foster is Professor of Sports Medicine and Director of the Human Performance Laboratory at the University of Wisconsin-La Crosse

 

In the past week we've watched the Olympic track and field events play out. Sprinting champions are likely to be Jamaicans or African Americans, whereas long distance champions tend to be Kenyans or Ethiopians, or from someplace not too far from the East African highlands. Do these seemingly typical talents and abilities for the relatively simple motor task of running reflect that some populations have a basic genetic endowment to excel in certain sport specialities?

There are data supporting the concept that there may be genes, or at least combinations of genes, that favor ‘speed’ or ‘endurance’. Evolutionary ‘trade-offs’ between different genes predisposing individuals to tend towards being ‘sprinters’ or ‘endurers’ would plausibly have been selected for different cultural-environmental settings. This can be appreciated by the R577X variation in ACTN3, a strong ‘speed gene’ candidate encoding α-actinin-3, a protein required for explosive muscle contraction. About 11% of the world’s population is α-actinin-3-deficient because of a genetic defect in both gene copies. The ‘null’ (XX) genotype, which - if you have it - decreases the likelihood of Olympic success in sprint events considerably, is very infrequent among Jamaicans and African Americans.

The R577X variant, appearing 40,000–60,000 years ago in Eurasia would have made humans slower and more enduring, potentially offering a survival benefit as persistence hunters. By contrast, in predatory animals or the prey for predatory animals, it is the capacity for explosive muscle actions that would have been selected for survival.

Yet, how the millions of variations in the human genome influence athletic performance, especially in endurance events, remains essentially unknown and no genetic test can really predict sports talent. A recent genome-wide exploration in 8 cohorts of world-class endurance athletes from different ethnicities and continents failed to identify a panel of genomic variants common to sports success.

That we are as still unable to identify single gene, or gene complexes, that consistently predict athletic success is more likely the fault of our analytic ability than the absence of relationship.  The population clustering of ‘performance types’ is too strong to support the idea that there is not a genetic basis (or at least bias) for performance. Williams and Folland proposed in 2008 that elite athletes are selected based on matching a fairly large array of genotypes; they suggested that 23 genotypes are required, and that the best athletes have the closest match to this genotype array.  On a purely commonsense basis, it seems likely that there may be more - say 50 genotypes for instance - that could contribute to high level performance in any particular event, and that an elite athlete has to have some fraction of these ideal genotypes, say 30 of 50, but that two more or less equal athletes may not have exactly the same 30 ‘champion genes’.

On this basis, the rapid improvement in world record performances since the end of the second World War could be attributed to the opening of competitive sport possibilities to a larger and larger fraction of a continually growing world population (e.g. there are more genetically gifted people in the population).  The flattening of the growth of world records is then reasonably attributable to saturation of the fraction of humans with sport as a possibility. We should not forget that until the middle of the 20th century Olympic sprinting was essentially unavailable to people of West African descent, for cultural and economic reasons; and that the Kenyan-Ethiopian breakthrough in long distance running was a function of developing economic possibilities in East Africa rather than this group of people suddenly learning to run.  The champions have always been there, but at certain parts of history they just weren’t at the Olympics.

Beyond genetic predisposition to a certain performance type, we cannot ignore the effect of opportunity, social support,  economic factors, and the willingness of individual athletes to work very hard to fully express their genetic potential as key factors for success.

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