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Is genetics responsible for athletic achievements?

The fastest man in the world, Usain Bolt, holds the world record for the 100-metre dash set in 2009 at 9.58 seconds, breaking the previous record of 9.74 seconds. Another extraordinary example is Michael Phelps, who has won 28 Olympic medals (23 of them gold) over the course of his career and set 39 world records, one of which has yet to be broken.[1]

Of course, all elite athletes must demonstrate an extraordinary commitment to their sport and have the resources and coaching necessary to train at the highest level. But another question inevitably comes up: Is there something in the genetic makeup of persons such as Bolt and Phelps that predisposes them to such athletic feats?

Sports genetics

Our scientific understanding of how genetics is involved in athletic performance is limited. Due to the complexity of sports genetics, it is difficult to determine which genetic factors help someone set a world record. However, scientists are beginning to understand how certain genetic factors can influence athletic traits.

We know that no single gene determines a person’s overall athletic ability, which is the result of complex interactions between several different factors. However, by peeling away the layers of different traits in athletic performance, it is easier to identify the genes that control them. For example, cardiorespiratory fitness and training response are two very important aspects of athletic potential. Studying either of these aspects reveals several underlying levels of complexity. For example, cardiorespiratory fitness can be measured as follows:

  • Maximal oxygen uptake (VO2 max)
  • Blood volume
  • Capillary density
  • Mitochondrial efficiency

Genes associated with athletic performance

Two of the most studied genes in sports genetics are ACTN3 and ACE. Both can influence the way that muscle fibres are produced. It should be noted that not all sports require the same type of muscle fibers to achieve optimal performance. Some sports require fast-twitch fibers while other sports require slow-twitch fibers.

Fast-twitch fibers

The gene associated with fast-twitch fibers is ACTN3. This gene provides instructions to produce a protein, alpha-actinin-3, which is very abundant in fast-twitch muscle fibers.[2] These fibers provides quick bursts of strength. Geneticists have discovered that certain versions of the ACTN3 gene are common in athletes who rely on strength and speed.[3]

Sports that require rapid muscle contractions include explosive sports such as boxing, baseball and the 100 metre dash.

Slow-twitch fibers

Other versions of the gene, such as the R577X variant, result in a complete absence of the alpha-actinin-3 protein, which appears to reduce the proportion of fast-twitch muscle fibers and increase the proportion of slow-twitch fibers.[4] Interestingly, some studies have shown that the latter version is more common in endurance athletes, such as long-distance runners and cyclists.[5]

Sports that require slow muscle contractions include endurance sports such as cross-country skiing, cycling and long-distance running.

Built to win?

These examples show that genetics probably has an impact on physiological traits that are important for athletic performance. However, the impact of genetics on other factors, such as personality traits (e.g., perseverance, courage) and intellectual abilities, is still largely unknown. In the cases of Bolt and Phelps, one only has to look at their body size and proportions to see that they must have received a few genes that gave them an advantage.

Although the challenge is formidable, one day we will improve our understanding of how genetic factors contribute to athletic performance. The debate will then begin as to whether genetics should be integrated into the mainstream of amateur and professional sports and, if so, how to do so ethically and fairly.

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  1. Allen Kim, “Two of Michael Phelp’s decade-old world records were broken this week,” CNN Sports, July 26, 2019. (source consulted May 12, 2021)
  2. Del Coso et al. (2019) More than a ‘speed gene’: ACTN3 R577X genotype, trainability, muscle damage, and the risk for injuries. Eur J Appl Phys 119: 49-60.
  3. Berman and North (2010) A gene for speed: the emerging role of alpha-actinin-3 in muscle metabolism. Physiology 25: 250-9.
  4. Miyamoto et coll. (2018) Association analysis of the ACTN3 R577X polymorphism with passive muscle stiffness and muscle strain injury. Scand J Med Sci Sports 28: 1209-14.
  5. Grealy et coll. (2013) The genetics of endurance: frequency of the ACTN3 R577X variant in Ironman World Championship athletes. J Sci Med Sport 16: 365-71.
Michel Cameron, PhD
Michel Cameron, PhD
Pharmacogenomics Director