41M 210lbs biceps issue.

I'm a very experienced trainer, been in the gym for many years of my life, starting with the army at 17 however I know you're never too experienced to learn something new in the gym world, that attitude keeps me progressing, however my arms (biceps) just won't widen. I have a 48" chest 34" waist and 17.5" arms. Anyone here could maybe suggest anything to add into a workout? I see videos on you tube but half of them are mega juicing and full of sh*t anyway. Any old school guys or new trainers have any little add ins for me to try? I train 4 times a week. Heavy and intense. I isolate my arms workout to one day on their own as opposed to to after chest/back etc Thank you in advance.