The ACTN3 gene produces the protein known as alpha-actinin-3. It provides structure within muscle fibers, contributing to increased contractile force and fiber strength.
There are two variants of this gene, one leads to production of a fully functional protein, the other leads to a smaller, non-functional protein. Having two copies of the fully functional “sprint” gene has been associated with elite-level power performance, while having two copies of the non-functional variant has been associated with endurance.
While there are many other genes involved in athletic performance, this is one of the best studied and most famous.