I have always wondered if high muscle weight slows me down in the same way as armor and weapons. Does none muscle weight make my character faster?

It has nothing to do with it, don't worry

Are you sure? Because some say it does, while others say it doesn't..

Well it's same like on World of Warcraft.
For example, if you take a gnome, he seems to be running so fast! Then you take Tauren, massive cow, and you think "Gosh it's so slow". And yeah, way they move it actually looks like it's a different speed, but they all have the same speed at the end.
Same will go for massive overmuscular Nord and perhaps tiny Breton. It looks like there is a difference, but they all have the same movement speed if they're without armor. I never seen no statement from Beth considering speed for muscular characters, and their differences. Don't missunderstand me, it would be realistic, but then muscular chars should do more melee damage, but they don't.
And even on PC, you can set up char's speed I think, at least you could in Oblivion. I remember it good, all characters had the same movement speed at the begining (from the same race ofc), because my mate was obsesed with differences between male and female chars in Oblivion. But speed and everything else was completely the same.