I hope muscle and weight is static, and you don't lose weight running around. Only when you work out.
Yes, it's unrealistic and they seem to be going towards realism with this.
I like having a character set up for me in the game, sure customizing him is nice and all, but I want to play as the protagonist. Not what I want them to be. When I played San Andreas, I kept CJ in his starting clothes, because that was what he looked like. Not what I wanted him to look like.