A group of fitness instructors are zapped by cosmic rays coming out of a gym late one night and transformed into super-ripped dinosaur people, who stalk the night as cold blooded superhero vigilantes.  In their free time, they search for a way to transform back into humans.

Eventually they discover an evil astronomer turned them into dinosaurs using cosmic rays he generated, as he was attempting to reverse engineer real dinosaurs from modern day birds, which he would then use to conquer humanity.  The fitness instructor dinosaurs do battle with the half-bird real dinosaurs, eventually beating the astronomer’s dinosaurs in a series of battles that look suspiciously like step classes and various powerlifts.  Finally, the leader of the fitness instructor dinosaurs fights and defeats the astronomer, but not before learning how to reverse their transformation.  Unfortunately this is all contingent on the head fitness instructor’s upper body strength, now lacking as he is a tyrannosaurus rex, and must do a one handed pull up to reach the lever on the cosmic ray gun that would reverse their transformation.