There's a fairly good Explainer up over at Slate on the subject of Congressional recess, but it doesn't really get at the main point. It simply isn't the case that the actions on the House and Senate floor are the main work of a Member of the House or a Senator. In my experience, most Members work pretty damn hard, but it's also the that some don't. None of that, however, has very much to do with how many hours the House or the Senate is in session.
Now, it's also true that a lot of what they do in a typical week are tasks directly or indirectly related to achieving re-election. But that's true whether or not Congress is in recess.