Clearly, some amount of fitness is genetic: you can’t expect everybody who follows the same workout to have identical results. It’s tempting to get tested to see whether you personally have the same genes as elite sprinters or weightlifters. But DNA tests can’t tell you much about your fitness, and it turns out that knowing your results may actually change how you feel and perform.
A recent study (paywalled, but summarized nicely here) tested 116 people for variations of the CREB1 gene, which is linked to aerobic fitness. Then they randomized the test results: half of the participants were told they had the “high risk” version of the gene, and half were told they had the “protective” version. But they deliberately gave some people the wrong results, just to see what would happen.
Then researchers asked the participants to do a treadmill test, and guess who had the worst outcomes? Not the people who had the “bad” genes, but the people who were told they had the bad genes. It’s the opposite of a placebo effect: sometimes, if you believe you’ll suck at something, you end up sucking at it.
This effect, sometimes called a “nocebo,” is actually pretty common. People who expect to feel pain are more likely to actually feel it; people who are told test results in a worrying manner can end up feeling more worry. The same researchers who did the treadmill test study also did a version where they told people that they had a gene that would make them feel more or less full. (That gene was our good friend FTO, which you may remember from this story about DNA tests for weight loss.) The results were similar: people responded in a measurable, physiological way to the genes they thought they had.
Now, the nocebo effect, like the placebo effect, doesn’t change your body at a nuts-and-bolts level. But when we’re talking about feelings like pain, or satiety, or fatigue, your brain filters information from your body. If you lie and tell a cyclist they’re going slower than usual, they can usually find it in themselves to speed up and break their own record.
It turns out that what you believe about yourself can actually affect your performance in the gym. So if you get a genetic test out of curiosity, don’t put too much stock in it. After all, there are far more factors in fitness than just a few DNA bases on a test report. Try telling yourself you’re awesome, and see what result that brings.