Before filming Rocky IV, director Stallone asked Lundren to add some extra weight, as he felt the Swede looked too lean for the role of the imposing Ivan Drago. This advice paid off in the way Stallone expected, but almost cost him his life. 
Trying to make the matches look as realistic as possible, Stallone also demanded the fighters throw actual punches while shooting. Lundgren obeyed, and hit Stallone so hard in the chest, his heart smashed into his rib cage, and caused swelling. For eight days the Rocky actor was in intensive care with a blood pressure above 200 and difficulty breathing.
