Split routines Tom's Weight Training Page Beginner and Intermediate routines. The reasons for doing split routines rather than full body workouts. When all of the is learned, you can progress to a routine that does all of these things better.
Intensity is learned, and mostly neuro-physiological.
After intensity is learned, you can train with an intensity that does not allow full recovery in a day or two. The increase in intensity is a real shocker to the system. Therefore growth results. The body does not like to change, and will get used to almost anything. To create change you have to shock the body into changing.