Flip a coin 100 times and chances are good it'll come up heads 50% of the time. Apply this to bodypart training and it's sort of like splitting it into just two workouts. Choice A might be the upper-body vs. lower-body split; choice B, another logical way to break it down, is the push vs. pull. Both systems of training are highly effective, and trainees typically choose one or the other when following the two-day split.
But, alas, this two-day coin has three sides, the third being a unique way to shake up your training by splitting your workout into front and back - something you've probably never considered. Here's how it works: You train the muscle groups on the front side of the body one day, then train the muscle groups on the back side on day two.
Each body part gets hit with both heavier weights in a lower rep range to build strength and size and lighter-weight, higher-rep sets to help build detailed, lean mass and strength endurance. The next time you train those body parts, the order is modified slightly with new moves inserted to stimulate the target muscle from new angles.
So in the end, you follow the logic of a smart muscle-building program that's just extreme enough to offer an altogether different approach.