Endurance is the skill you want for additional carrying capacity. The way it works is that there are "break points" for how your character acts under certain equipment loads. At less than 25% equipment burden, you will move very quickly and have fast, long rolls. Above that, you will move somewhat slower and have a slower, shorter roll. Once you get to 50%, you will move significantly slower and will now be doing what is known as the "fat roll" where you sort of throw yourself to the ground, and won't dodge effectively at all. Once you get to 100%, you're restricted to walking and can't roll at all.

It's how the game balances the lighter armors vs. the heavy armors - lighter armors if you get hit, you're in trouble, but you have better dodging capability. The heavy armors, you can't dodge so well, but you can take a few hits and get interrupted less.

Mages tend to favor light armors to help them keep at range and because the Endurance required to equip the really heavy armors makes it difficult to also afford the Intelligence requirements and the cost of the spells themselves.