When It Comes to Weightlifting, Genetics Can Do a Lot of the Heavy Lifting

If swole is your goal, there are many possible paths to improved strength: a good training regimen, a healthy diet, adequate sleep hygiene, and anabolic steroids.

But research conducted over the past two decades has discovered that many elite athletes in sprinting and weightlifting also share a common genetic variant that may partially explain their successes in these sports. The ACTN3 gene encodes a protein called α-actinin-3, which is found within the fast-twitch fibers of muscle—a necessity for generating rapid, forceful contraction in activities such as sprinting and weightlifting.

The ACTN3 gene comes in two forms: there’s a normal, functional version called 577R, which allows people to produce α-actinin-3 protein in their fast-twitch muscle fibers, and a “defective” version called 577X, which has a single base change that prevents the production of α-actinin-3. Individuals with two copies of the 577X version produce no α-actinin-3 in their fast-twitch muscle fibers. The frequency of the 577X variant differs around the world, but overall somewhere between one-sixth and one-quarter of the world’s population has two copies of 577X, and are thus completely deficient in α-actinin-3 (encompassing at least a billion people worldwide, with the lowest incidence rates found in Africa).

Fear not: a lack of α-actinin-3 won’t damage your muscles or cause them to wither away, much less prevent you from eventually growing them to Schwarzenegger-esque dimensions. But the presence of the functional version of ACTN3, 577R, may have a positive impact on a muscle’s ability to generate explosive power. Many studies involving small samples of Olympic-caliber athletes—small because there are only so many such elite athletes to go around, and only so much time for them to be involved in scientific studies—have found varying levels of performance enhancement, with a consensus emerging that the presence of 577R can explain roughly two to three percent of the variance in strength and sport performance among the general population.

Because the public now has access to extensive genetic testing options, you can learn whether your ACTN3 gene expresses the 577R or the 577X variety. In the course of writing this article for Motherboard, I contacted 23andMe, one of many such testing services, to schedule my own DNA analysis. I had excelled at sprinting in high school and college, and had no real powerlifting learning curve when I began pursuing that sport. That said, given the very modest boost to performance afforded by 577R, neither outcome would have stunned me.

The author’s results from 23andMe. Image: Oliver Lee Bateman/Motherboard

Finding out that I lacked the 577X mutation hardly came as a shock, nor did many of the other results, such as learning that there was a strong likelihood I had blue eyes as well as a 60 percent chance of not having a widow’s peak (although I did discover that I had a not insignificant amount of relatively recent West African ancestry, thereby confirming one piece of disputed family lore).

Much more research will need to be done before we can expect to find ourselves facing legions of designer babies that resemble myostatin-inhibited “bully” whippets or Belgian Blue cattle. For starters, ACTN3 is only a tiny piece of the puzzle in terms of muscular development. A far greater mystery, but one which scientists have repeatedly refused to explore, on ethical grounds, is whether certain humans have a genetic predisposition to tolerate enormous doses of anabolic substances and other performance-enhancing drugs.

A wealth of anecdotal evidence suggests that some superior athletes, such as baseball MVP Barry Bonds and ex-college basketball player turned bodybuilding champ Phil Heath, can respond very quickly to anabolic drug regimes.

“They call Phil Heath the ‘Gift’ because he’s such a natural specimen, but I think his real gift is that nobody looks as beautiful on the juice as he does,” amateur powerlifter Aaron Cook told me at this year’s Arnold Classic bodybuilding show. “Most people, they’re like me, huge but puffy, big slobs with back acne… to look so good on steroids is something you’re just born with.”