Zombies will not be super strong, but they will be stronger.

Every person has a set amount of strength. But they can only access part of it. There are safety's in our brains built in to keep us from over using our muscles and hurting ourselves. When you weight lift you are teaching your body that you can change the safety's. It's why you don't see muscle growth when you first start working out. There are times when the safety's can be overridden, such as when a mother has a baby stuck under something. With most of the brain function not working in a zombie these safety's would be turned off, allowing the zombie to access it's complete strength, even if it meant doing damage to itself. This is something to keep in mind when you think about zombies, yes it won't be super strength, but your friends, family, neighbors, community will now all be stronger than you remember them, they will be able to do more destruction and therefore require better barricades.