Blades vs Muscle Back

Do you all find a difference in their forgiveness or feels the exact same?

Can you elaborate on two iron models that you are comparing? ‘Blades’ and ‘muscle backs’ are generally considered synonymous.

Blades would not be cavity backs.

I consider muscle backs to be the irons with more or thicker mass behind the sweetspot.
I think of MacGregor M85, or DynaPower to be classic muscle backs.