DESCRIPTION
The doctor uses an experimental treatment to give you favorable genes for rapid muscular growth. You respond exceptionally well to his treatment. However, there's an interesting side effect... When you workout, it feels more than pleasurable. It feels orgasmic.
There is a brief mention of a "syringe" and a painless "injection." The science here is pretty vague... just don't think about it too hard and let the doc do his thing, lol