There is no evidence that ultra-high doses of steroids alone will cause muscle growth through a chemical effect.
Anabolic steroids act on the balance between anabolic and catabolic processes within the body.
Anabolism is the constructive process by which simple substances are converted to more complex compounds, such as bone and muscle tissue. Catabolism is the corresponding destructive process which breaks down these complex compounds for removal from the body. The state of anabolism and catabolism may be measured by evaluating the body's nitrogen balance. They are believed to diffuse into the cellular cytosol and bind to the androgen receptor. The newly formed receptor-steroid complex migrates to the nucleus, interacts with the DNA and initiates transcription.