Are you genetically predisposed to excel at power sports? A variation in a gene known as ACTN3 may determine if you’re better suited to sports like sprinting and weightlifting, or if you’re better off focusing on endurance sports.

A 2003 study published in the American Journal of Human Genetics discovered a link between variations of the ACTN3 gene and elite athletic performance. The ACTN3 gene is responsible for producing a protein, known as alpha-actinin-3, which helps regulate the function of fast twitch muscle fibers. Fast twitch fibers, also known as white muscle fibers, fire more rapidly and generate more force than slow twitch fibers. These muscles are capable of the rapid, forceful muscle contractions necessary in speed and power sports such as sprinting and weightlifting. Some people, however, have a non-functioning version of the gene, which prevents production of the muscle protein.

Researchers in the study looked at different combinations of the ACTN3 gene, which can be either functioning or non-functioning. The functioning version, or the R variant, instructs the body to produce alpha-actinin-3. The X variant is non-functioning, and prevents production of the protein. Because humans have two copies of each gene, one from each parent, possible combinations of the ACTN3 gene are two R variants, two X variants, or one of each.

Scientists examined the genotype of elite athletes from 14 different sports. They discovered that more than 97 percent of Olympic-level sprinters had at least one functioning R variant. All female elite sprinters had at least one copy of the functioning gene.

The functional version of ACTN3 is seen in high frequencies in other elite power athletes as well, such as weight lifters. Ethnically speaking, Africans have the lowest incidence of the X variant, while Asians have the highest.

Among the general public, about 80 percent of people have at least one functional copy of the gene. More than a billion people worldwide have two X variants, meaning they completely lack the protein. A lack of alpha-actinin-3 doesn’t have any harmful health effects, but it may result in less muscle power. Athletic ability in other areas, however, should not be affected, as athletic performance is determined by a wide range of environmental and genetic factors — including at least 200 other genes — which aren’t fully understood.

Two non-functioning genes doesn’t necessarily preclude athletic ability, however. A lack of alpha-actinin-3 may actually be related to endurance performance. In the study, nearly 25 percent of elite endurance athletes had two copies of the X variant. And an Olympic long jumper from Spain was found to have two non-functioning copies of the ACTN3 gene, indicating that athletic success is influenced by numerous factors.

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