In bodybuilding terms, this overmuscled sequel to ''Pitch Black'' is all bulk and no definition. In touch with the grunting, preening culture of professional wrestling, the negligible screenplay by David Twohy, who directed both movies, is crammed with trailer-ready tag lines. Intoned by its star, Vin Diesel, with a sly comic gravity, these enigmatic blurbs mean next to nothing. But who needs narrative coherence, or even literacy, anyway? If you can dead-lift 300 pounds, you're the man!