Arnold Schwarzenegger called Max von Sydow the first "incredible dramatic actor" he ever worked with. He finds von Sydow's performance "staggering."
Arnold Schwarzenegger and Sandahl Bergman did their own stunts, as suitable body doubles couldn't be found.
Arnold Schwarzenegger had weapons training, martial arts training, and horseback riding lessons from specialists. He trained with an eleven-pound broadsword two hours a day for three months; each broadsword cost $10,000 and had to look weathered. He also learned climbing techniques, and how to fall, roll, and jump from fifteen feet in the air. John Milius made sure all of these were videotaped, and according to Schwarzenegger, they were just as intense as training for bodybuilding competitions. Franco Columbu was his trainer and was rewarded with a small part in the film.
James Earl Jones was a last-minute addition to the cast because of his commitments on Broadway. He and Arnold Schwarzenegger became friends on-set; Schwarzenegger helped Jones stay in shape and Jones (as well as Max von Sydow) coached Schwarzenegger on acting.