I'm still trying to figure out how that would work, wouldn't it be "unstoppable force meets immovable obje... Snap! ... well nevermind."
No, I figure it's like two (well-muscled) normal men struggling against one another. Their superstrength/invulnerability cancel out. A normal man can break another normal man's neck, so Clark could break Zod's neck.
(Good thing for the mooks--uh, I mean, hapless civilian family, that apparently you can only shoot your heat ray vision straight ahead. Else Zod could have just, you know, glanced their way and incinerated them despite Clark's neck hold. I'm just sayin'....)
Man, that movie sucked is so many ways. I have a new appreciation for Superman Returns now. It was very, very problematic too, but there are ways in which it was far superior to this mess.