The injury to Stallone prevented him from throwing anything but quick, close quarter uppercuts. A story by Turner Classic Movies revealed that certain shots of the epic boxing sequence had to be filmed in tight closeups, which ended up working because the script called for Rocky to embrace his Southpaw style and fight with a left-handed attack. Because of the script change, they managed to complete the shots needed to make the fight work. 

The way both actors were going at it, Stallone and Carl Weathers might as well have been in a real fight. In an interview with Roger Ebert in June of 1979, Stallone touched on the extreme level of punishment he endured. “I got all beat up inside, I had to have an operation to splice things back together,” he said. “The mouthpiece saved my teeth. For this one, basically what I need is a mouthpiece for my whole body.” 

In the second part of that interview in July of 1980, Stallone revealed that he had to undergo extensive testing after he suffered broken bones along with “enlarged intestines, rearranged insides” and a significant amount of weight loss. The “Rocky II” fight was also much more extensive than the brawl that went the distance in “Rocky.” “The fight’s four times as long and has eight times as many punches as the first one,” explained Stallone. “A lot of those shots aren’t faked. It’s as hard to learn not to hit somehow as to hit them.”