Scientists unpack how your unique genetic makeup could affect your performance gains — and how heavily you should consider it when training.
If you’ve ever left a class feeling like you just weren’t built for that type of workout, you’ll understand the appeal of fitness-focused, at-home DNA tests. Purchase a kit and spit into a tube, and you could ostensibly learn how to create a fitness program that’s tailored to your genes. You’ll get advice based on whether you’re wired to benefit more from a focus on strength vs. endurance, as well as how easily you recover.
Multiple direct-to-consumer brands already offer these types of tests, but they may be providing suggestions based on speculative science.
Here, geneticists weigh in on how your genes influence your optimal training style, and whether existing at-home DNA tests can provide practical insights.
How Your Genes Affect Your Response to Exercise
Research indicates that your genes play a role in how your body reacts to exercise. “Say we take a thousand people and they all follow the same exercise regimen,” says Claude Bouchard, Ph.D., a professor emeritus and senior endowed chair in genetics and nutrition at Louisiana State University. “They’ll have very large individual differences in the gains that they experience, whether it's endurance performance, maximal exercise capacity, muscular strength, or power.” In other words, some of those people will, for instance, become much stronger, while others will gain very little strength from the same program.
Furthermore, studies have found that relatives tend to have similar responses to exercise, Bouchard says. “When we repeat the experiment, but this time with members of families or pairs of identical twins, we see that the more people share ancestry genetics in common, the more similar they are in their response to the exercise regimen,” he says. (Bouchard authored a 1998 study in which this was reflected in participants’ VO₂ max, i.e., the maximum amount of oxygen their bodies can use during intense exercise.) “So this strongly suggests that there is a genetic basis for the ability to gain from exposure to a standardized dose of exercise.”
While it’s clear that certain genes play a role in exercise response, scientists are still working out exactly how to use someone’s genetic characteristics to predict whether they’re a “high responder” or “low responder” to different types of workouts, according to Bouchard.
“Scientists have been trying for about 20 years to do just that,” he says. “...Everyone has tried, but we have misjudged, to a certain extent, how the genes are interacting and coming into play to determine the ability to respond.” Thousands of genetic markers — and the complexities of how they interact with each other — likely play into a single trait, such as maximum exercise capacity, he explains.
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“In general, I don’t think the field is advanced enough to precisely match DNA with training,” echoes Michael Snyder, Ph.D., a professor of genetics at Stanford and co-founder of January AI. “There have been studies linking certain gene variants with cardiovascular function, but these effects tend to be modest. One of the better-studied genes is ACTN3, which encodes α-actinin-3; certain variants have been associated with higher risk of muscle injury.”
Still, existing research isn’t sufficient to conclude that people with the variants should be more cautious about how they approach strength training, he says.
Are Fitness-Focused DNA Tests Worth It?
At-home DNA tests that promise tailored fitness advice may be based on premature scientific conclusions. “Companies are offering formulas to help you understand if you are a good responder or poor responder or whether you are gifted mainly for endurance activities or power and strength activities,” Bouchard says. “And these we cannot predict properly.”
Snyder has a similar read. “While interesting, the utility of these tests remains unclear at this point,” he says. “...In general, their recommendations are still limited by the state of the science, which doesn’t yet allow for robust, individualized training prescriptions based on DNA alone.”
DNA tests may eventually play a role in performance optimization one day, Snyder adds. “What I find especially promising is going beyond DNA to integrate ongoing, real-world health data.” For example, this could mean factoring in your real-time dietary choices and sleeping patterns, too, so that you can base your training on multiple data points rather than your genetic predispositions alone, he explains.
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Companies are offering formulas to help you understand if you are a good responder or poor responder or whether you are gifted mainly for endurance activities or power and strength activities. And these we cannot predict properly.
The path to a sound fitness-focused DNA test may take years, if it happens at all, Bouchard says. “The entrepreneurial spirit is likely to want to bring this to the masses, but it would not be a simple thing — very elaborate and quite likely expensive,” he explains.
In the meantime, the best way to optimize your fitness routine is to follow general recommendations or to work with a personal trainer, Snyder says. They can help you map out a plan with a personalized balance of resistance training, cardio, and rest for your abilities and goals. For now, you can simply tune into how you feel and progress with different kinds of exercise — no spit test necessary.