text: He would definately gain muscle.  Cardio really isnt great for building muscle- especially if you are doing it for a long time (running distance, biking long ways, etc).  Cardio is an equal opportunity burner of stored energy- which is both fat and muscle mass.  There are a couple of problems with fat guys doing only lifting.  The first is that you're a lot more likely to have a heart attack or annurism while lifting if you're real heavy.  The second is that you're not going to look cut when you're fat- the fat just sits on top of the muscle and hides it, so you still look fat, not cut.