What does nandrolone decanoate do for bodybuilding? Nandrolone decanoate is a synthetic anabolic-androgenic steroid (AAS) that is used in bodybuilding to increase muscle mass, strength, and endurance. It is sold under the brand name Deca-Durabolin, and it is one of the most popular AAS used by bodybuilders. Nandrolone decanoate works by increasing protein synthesis in the body, which leads to …