Sports slacker or sports fanatic: What role do genes play?

Everyone remembers it from school sports – while some can score every goal and climb ropes with ease, others struggle with it. They trail half a lap behind the others when running and are always picked last when forming teams. But why is it that there are sports enthusiasts and slackers among children and adults? Is there perhaps a (non)sportsmanlike gene?

Whether and to what extent our genes influence our athletic performance has long been researched. But it's complicated, says Billy Sperlich, a professor at the Institute of Sports Science at the Julius-Maximilians-University of Würzburg. For one thing, there is only a limited number of high-performance athletes available as study participants. Furthermore, the question arises as to how athletic performance can even be clearly defined. How, for example, should one measure the performance of a soccer player?

Comparative studies can only work if they focus on specific aspects such as strength or endurance, says Sperlich. In most sports, however, various skills that contribute to performance are intertwined: "Many endurance athletes, for example, do an extremely high amount of strength training, and the two cannot be clearly separated."

A true endurance sport might be middle- and long-distance running. And certain genetic abnormalities have indeed been identified in track and field athletes who practice this sport. They are more likely to have a specific form of the ACE gene, the ACE II genotype. The ACE gene contains the blueprint for an enzyme that produces angiotensin II from a precursor of the hormone. This, in turn, regulates blood pressure. And appears to be able to influence muscle endurance performance.

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Athletes who run fast, short distances require a different kind of performance. And they, too, have innate characteristics that often make extremely good performances possible. "Genes explain a lot here. You have to be born a sprinter," says Sperlich. It has been found that a specific expression of the ACTN3 gene (ACTN3-R allele) favors the necessary explosive power. The gene causes someone to have more fast-twitch muscle fibers, which are needed for fast running, while long-distance runners benefit more from slow-twitch muscle fibers.

"ACTN3 and ACE are the best-researched genes in the context of athletic performance. Their role has been demonstrated by numerous studies and meta-analyses," summarizes Sperlich. "The ACTN3-R allele favors explosive power, while the ACE-II genotype favors endurance performance."

There are other genes that have an influence, but these are usually smaller, more complex, and less well-documented. Of course, genes alone don't make an athlete. "Environment, training, and nutrition also play a crucial role," emphasizes Sperlich. "Genes are the foundation. Performance is enhanced through training."

Because there are many other influencing factors, it's impossible to predict exactly how good someone will be at a sport based on genes. Conversely, however, it's very likely that athletes who achieve Olympic success also have the best genes for it.

There's no genetic makeup that necessarily makes you unathletic. However, it's clear that not everyone has the same basic prerequisites. And some people simply weren't given certain advantages by nature. This is also noticeable in the recreational sports sector. "There are people who go to the gym once or twice a week and can build muscle very well that way," says Sperlich. And there are people with a different genetic makeup: "They might have to go three or four times a week to achieve the same effect."

In competitive sports, where everyone trains extremely hard, such differences can eventually no longer be compensated for. Therefore, those with the "more athletic" genes are more strongly represented.

In some cases, genes indirectly influence athletic performance by programming individuals for a specific body type. For example, long-distance runners are particularly well-advanced to have long legs but relatively small calf muscles, explains Sperlich. These physical characteristics are found – genetically determined – in many Kenyan runners who are extremely successful in marathon races.

However, other factors play a role here, such as the social component, says Sperlich: Those from economically weaker countries often have a particularly strong motivation to succeed in professional sports. Even in these cases, it's impossible to clearly distinguish what influences performance the most, says the sports scientist. Sport is never purely muscular, but always a matter of the mind: "The psyche and other organ systems play a role. Blaming genes alone for performance never really works. We have to keep things in perspective."