@lonelygod - It seems to me that bigorexia would require the men to be unable to see how much they have accomplished. If the guys at your gym are showing off their body work, I doubt they have the disorder. I think that someone with bigorexia would be way more concerned about keeping to themselves and constantly improving.
If I remember correctly, I read somewhere that most people with bigorexia are pushed into treatment by loved ones, much the same as with anorexia. As far as how many men suffer from bigorexia. I am sure it's many more than are currently recognized.