Training most body parts once a week to "allow for adequate recovery" is soooo 20th century. I've been training for almost 30 years now and I really wish it hadn't taken me about 25 years to figure that out. I stayed stuck to the body part split for far too long. Increasing my frequency in the past few years has led to almost as many gains as I had in the first 25.
Let's use chest training as an example. So Monday is chest day, right? Flat bench, incline dumbbells, decline bench, incline flyes, pec deck, and cable crossovers. That sounds like a pretty standard International Chest Day workout, doesn't it?
So here's the thing: When you kick the crap out of your chest for an hour and a half on Monday, then spend the rest of the week "recovering," you're absolutely, no questions asked, 100% guaranteed, leaving potential growth and strength development on the table.
Why? Because protein synthesis (rebuilding damaged muscle tissue post-workout) stops within 48 hours or less after you train. So you annihilate your chest on Monday, rebuild it on Tuesday (maybe a little on Wednesday morning too), then spend the rest of the week chest-stagnant.
What if you hit chest Monday, Wednesday, and Friday, for example? Monday, Wednesday, and Friday, you stimulate; Tuesday, Thursday, and Saturday, you synthesize. While it might not literally triple the growth, it's definitely a whole lot more growth than you'd get in the first scenario.
Now do the same thing for every body part. You're accelerating your progression like crazy.
Of course, you can't train with the same amount of volume if you're hitting every muscle two or three times every week, but a good push-pull or push-pull-legs split will allow you to hit the sweet spot in terms of your frequency/volume balance.