When Colorado-based Atlas Sports Genetics started offering its “SportsGene” test in 2008, zealous parents rushed to uncover their children’s
athletic destiny. “The results have helped us immensely,” one Texas mom wrote in a testimonial. “We have changed his extracurricular activities to
be more in line with the test results.” Atlas offers a $169 test of the ACTN3 gene, which, according to an Australian study from 2003, can indicate
whether you’re best suited to endurance sports, sprint and power sports, or a mix of the two. Whether or not the test imparts useful information—
which is still very much up for debate—you probably shouldn’t choose how your two-year-old spends his or her playtime based on dreams of future
athletic glory. But it’s impossible to deny that your genes do play a role in your athletic destiny.
According to a 2006 study of over 85,000 twins in seven countries, about 62 percent of the variation in exercise participation seems to be
inherited. This could be because of personality traits that run in families—people who are self-disciplined tend to exercise more, while those who
are anxious or depressed exercise less—or physiological differences such as the production of feel-good dopamine after vigorous exercise. The
genetic tendency to lose weight or gain muscle could also make some people more likely to exercise than others.
All of this suggests a certain inevitability: either you were born to exercise or you weren’t. But in the years since that study, something
interesting has happened: the search for the “exercise gene” has run aground. Several studies have analyzed the DNA of thousands of people,
looking for the sequences that predict exercise behavior—and they’ve found not one but many. A 2009 study of 2,600 Dutch and American adults
found 37 different DNA regions that were linked to exercise, and these regions were entirely different from the dozens of regions identified in
previous studies. In other words, there isn’t an exercise gene—there are hundreds of different genes that combine to influence every aspect of our
behavior. Nobody has all the “good” genes, but neither does anybody have all “bad” ones. So even if you have difficulty, for example, with losing
weight, you’re likely to be ideally suited for some of the other mental and physical benefits of exercise.
The idea that your exercise destiny is preordained took another blow from a 2009 study that examined the links between physical fitness and
intelligence in 1.2 million Swedish men who enlisted for military service between 1950 and 1976. Among these men were 6,294 twins, which
allowed the researchers to separate the effects of nature from nurture. They found that those who increased their cardiovascular fitness between the
ages of 15 and 18, a time when the brain is developing rapidly, scored better on cognitive tests and went on to greater educational achievements
later in life. Crucially, more than 80 percent of the differences between subjects were explained by environmental factors, while less than 15 percent
could be attributed to genetics—a powerful illustration that, while genes might affect how our bodies respond to exercise, the choice of whether or
not to exercise still resides with each of us. So if you’ve been blaming your DNA when you slack off your exercise routine, you’ll have to find a new
excuse!
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