Sylvester Stallone decided that for the shooting of the fight, he and Dolph Lundgren should hit one another for real, so as to increase the intensity of the scene. After doing three takes of Rocky taking shots to ribs, Stallone felt a burning in his chest, but ignored it. Later that night, he had difficulty breathing and was taken to a nearby emergency room. It was discovered that his blood pressure was over 200, and he had to be flown on a low-altitude flight from Vancouver, Canada to St. John's Hospital in Santa Monica, where he remained in intensive care for four days. What had happened was that Lundgren had punched him so hard in the chest, Stallone's heart had slammed up against his breastbone and began to swell, cutting off the blood supply and restricting the oxygen flow throughout the body. . However, when asked about whether or not it really happened while answering a series of fan questions in a 2021 interview with the Guardian, Lundgren claimed to have no recollection of the incident. "I don't know," he said. "[Stallone] keeps talking about it, so maybe he's right. He did go to the hospital, but I don't know whether it was my punches or the fact that he was so overworked as the director, actor and writer. We shot those 15 rounds over two or three weeks, eight or 12 hours a day, so you're throwing thousands of punches. If you don't connect, it looks a bit fake, but it doesn't mean you want to hurt the other guy. But there were no hard feelings." He went on to explain that stand-ins and stunt doubles were rarely used, and that he has performed the majority of his own stunts and fight scenes--but that this has changed in more recent years. "Back in the day, you had to do it all yourself: Rocky IV, The Punisher, Masters of the Universe, all the Expendables," he said. "I've jumped from a motorcycle to a truck; dangerous things I would never do now. Staying physically fit over the years has been nice. There aren't many actors who can stay physically fit for a long time. Part of the game is trying to look fit, at least."
"Rocky IV" became the highest-grossing film in the "Rocky" series to date, taking in just over 300 million dollars worldwide.
During filming, Dolph Lundgren and Carl Weathers really did not get along and got into an altercation. Lundgren threw Weathers into a corner of the boxing ring. After that, Weathers shouted profanities at Lundgren while leaving the ring and announced that he was calling his agent and quitting the movie. Only after Sylvester Stallone forced the two actors to reconcile did the movie continue. This event caused a four-day work stoppage while Weathers was talked back into the part and Lundgren agreed to tone down his aggressiveness.
James Brown is seen performing the song "Living In America" prior to the Creed vs. Drago match. The song was released as a single from the movie's soundtrack and became Brown's first Top 40 single in eleven years, and the last of his career.
Arnold Schwarzenegger helped train Dolph Lundgren to make sure he was in the right shape for the film.