There is nothing inherently wrong with a traditional body part split routine. As long as you are performing enough sets to stimulate growth, your body will grow. The question really falls under what's more optimal for a lifter.
Why Does Everyone Do Body Part Splits?
These routines got super popular through muscle magazines. They would put workouts of famous bodybuilders like Arnold who utilized these approaches. The issue here is, most bodybuilders are either genetically gifted to pack on muscle, or on anabolic steroids. Again, nothing wrong with either of those but if you are a natural lifter with average genetics then you simply won’t get the same results. These guys will get big regardless of the workout they do, they just need to push hard. If anything, having those advantages is what makes a body part split so ideal for them because they can handle the higher volume in a given session and still grow.
The research shows when we hit a given muscle with sufficient volume, we maximize the muscle building signal. This is usually 4-8 sets per muscle per session. Any more than that should be split into another workout. After about 48-72 hours that signal comes back to baseline, so hitting it again a second time will send that signal right back to its peak allowing you to maximize how much muscle you build.
The Full Body Advantage
I used to be SO against full body workouts. I would see a workout plan and think to myself “how can you possibly get any growth from only doing that many sets at a time?!” I had to do it to believe it myself. The other advantage aside from the signal spike is your recovery. We ultimately build muscle when we can use the heaviest weight, or more reps than the previous workout. By the time you get to your last two leg exercises in a body part split routine, you are probably cashed out. Your legs are tired, and thus you have to use less weight. Using a full body routine allows you to save those last exercises for later in the week, and hit them fresh which potentially allows you to use more weight than keeping it all on one day.
Recovery is the time spent so our muscles can adapt. If we know that 4-8 sets is the optimal range per muscle in a given session, what added benefit is doing any more than that versus splitting it up? If anything now you’re running the risk of doing TOO much and not letting your body recover in time. On top of that, you are letting that muscle wait 7 days before even hitting it again. Not optimal.
Follow The Program You Can Do Consistently
At the end of the day the choice is yours. An okay program followed consistently will outperform the perfect program hardly followed. I loved body part splits for my clients because their schedules were always shifting. By having 2-3 full body sessions, even if I only saw them once that week, we at least hit everything. A body part split doesn’t allow that, and you may only work half your body on a given week. It gives you a nice flexibility to work around your schedule and not vice versa.
If you’ve been doing a split for a while now, I highly recommend switching to a full body routine. It’ll create a new stimulus that will provide ample signals for growth, and give you something new to look forward to in the gym. It may even break any plateau you had.
Be sure to check out my article on What is a Good Resistance Training Program for a Beginner or The Best Lifting Routine for Skinny Guys if you want further detail on how to program a full body routine.