Different ways to skin a cat.
IMO, as long as you're incorporating essential compound lifts into your workouts (ie. deadlifts, bench press, leg press, squats, cling & press), your arms will be good to go if you hit them once a week in addition to your other upper body workouts. It's all about release of growth hormone.
Do deadlifts and clings on back day.
Do squats and leg press (one-legged works well, too) on leg day.
Obviously do bench on chest day.
Working out your arms and legs on the same day doesn't give you much of an advantage. However, you will hit your arms harder because they are less fatigued.
My current workout is an upper body/lower body split, 2 times a week.
Monday/Thurs. - chest, back, shoulders, arms.
Tues/Fri. - legs
I only throw in one set of arms at the end of upper body days.
I notice that when I'm tired I will slack on arms and won't be sore the next day.
If you have the endurance to work them out properly you will definitely benefit from this, though.
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