The difference between endurance and power athletes

It’s in your genes.

For only $169, there’s a small warehouse in Boulder, Colorado that will ship you a kit to tell you exactly where your child’s athletic potential lies. To use the kit, you simply swab the cheek of your potential Usain Bolt and ship it back to the lab for analysis.

According to their website, it’s “recommended for all athletes… to help interested individuals find their potential.” It’s specifically marketed to kids younger than eight years old, since they aren’t really able to do physical tests like vertical jumps or VO2max testing to reveal their athletic abilities. Sorry California and New York residents, your states have laws preventing this type of DIY testing, so it’s unavailable to you.

How could a cheek swab tell you about your athletic potential? Genetics. The test claims to describe  ACTN3 gene, which is one important little gene out of about 20,000 in our genome. There’s a significant association between the ACTN3 gene and athletic performance, specifically in sprinters.

If your kid has the sprinter-type of the gene, he should theoretically play sports that utilize speed and power. If he doesn’t have the sprinter-type ACTN3, he should focus instead on endurance events.

However, in the age of precision, personalized medicine which is based mostly on genetic predispositions to diseases (and hasn’t really been successful), utilizing a test like this to try to gain a competitive advantage could be problematic. Obviously athletic potential is a product of more than one gene, and there’s always the possibility that tests like these could place added pressures on young athletes, which almost always lead to poor outcomes. 

These types of genetic tests beg the age-old question on genetics and sport. How much do genetics really contribute to athletic ability? Some research in twins indicates that contribution is as high as 60%. It’s tough to experimentally differentiate between adaptations from training alone, or from some genetic advantage.

There’s a difference between correlation and causation. Sprinters are known to have a larger proportion of type IIx muscle fibers, or the fast-twitch power fibers, and endurance athletes are known to have more type I fibers, or the slow-twitch “aerobic” fibers.

But are those sprinters born with more power fibers, or does sprinting change the composition or recruitment of their muscle fibers? A recent study shows some cool data on the potential difference between “nature and nurture.”

The researchers took biopsies (small muscle chunks) from the leg of a former 110-meter hurdles world record holder, and current 60-meter world record holder. 71% of his muscle fibers were of some fast-twitch variety, and 24% were “pure MHC IIx,” or the fastest of the fast-twitch fibers. According to the authors, that’s the highest abundance of IIx fibers ever recorded. And it’s almost certainly due to genetics.

But in addition to the high abundance of those power fibers, his IIx fibers had off-the-charts power outputs, and were highly responsive to adaptations after a training session. In fact, the authors concluded that the power output of the athlete’s fast twitch fibers were “greater than any human values recorded to date.” The ability of those fibers to produce power and adapt came from years of highly specific training.

In other words, genes establish our biological composition, and place limits on our athletic potential. Training is what gets us to that limit.

So, in the words of Per-Olof Astrand, the Swedish father of exercise physiology, “to be an Olympic-caliber performer, you must choose your parents wisely.”

Photo credit: Kristian niemi/flickr creative commons
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