there is a theory that steroid hormones at a certain level (e.g. 600mg testosterone or more per week) can cause muscle satellite cell fusion into muscle fiber cells. Therefore, a user might end with more muscle cells after a steroid cycle! He would have altered his body composition permanently. This is not hyperplasia of muscle cells but something that has the same effect and what can be called a permanent gain.
read
http://www.thinkmuscle.com/articles/haycock/androgen-receptors-02.htm
read
http://www.thinkmuscle.com/articles/haycock/androgen-receptors-02.htm