The next big thing vs steroids is gene therapy, and there will no test to detect it. Its already being used. Results never go away, until normal aging sets in.
They will be able to enable athletes to have either more red, or white muscle, combination of fibers, depending on their particular endeavor, and natural Red/White proportion vs what the individual athlete was born with. Will also be used for muscle wasting. Thats the main reason for the creation.