I just found out about P90x and it seems they use the muscle confusion theory. But how does it work neurologically and as far as creating muscle mass is concerned? What would a typical routine be? Examples please.
The phrase is a marketing slogan.
That said, it is based on the principal that if you do the same thing time and time again, your gains will plateau at some point. By varying what you are doing and targeting the muscles in different ways, it will take your body longer to "get used" to a particular routine/exercise which results in plateauing.