The filmmakers also talked about how they scripted this Arnold vs Lou thing as sort of a "David vs Goliath" or a kind of an attempt as a "Good vs Bad" scenario - sort of the WWE type of drama. If I recall correctly, they originally wanted to portray the dark, brooding, larger Lou as the "villain", and Arnold as the good guy and underdog. If that was true, it certainly didn't work out that way. For obvious reasons, the exact opposite impression came across on-screen.
Lou even wrote (or more likely had ghostwritten) in his autobiography of some of the unrealistic embellishments of the movie - mainly that the apparent close, supporting relationship he and his father had in the movie was a sham. He claimed that his father was always an obnoxious, psychologically abusive egomaniac who insisted on being part of the movie to satisfy his own selfish desires. Of course I realize that there are two sides to every story, and I tend to take anything Lou says with a grain of salt anyway - for obvious reasons.
In the special features on the 25th Anniversary DVD, they say that the original storyline was supposed to be about this new wunderkind Lou coming and beating the reigning champ for the Sandow.. However, they state that as they got closer to the show they realised that Lou wouldn't get anywhere near Arnold so had to 're write' the script and make Arnold the mean guy to make it interesting..