That would be Coggan's area, or a coach's area - I need to go back to listen to that podcast that spurred the Rappstar post that inspired me to check it out. My thoughts are completely observational based on my PE and wanting a number to help me plan better.

edit: not to pass the buck, but my thought is just that I want to prevent overtraining while pushing myself, and not treating it as an art. I went back and analyzed years of past training, and I went through, using the TP workout planner, and figured out the TSS for each workout in a Lydiard style plan just to see how that progresses. I'm sure I'll keep changing things up; I'll read the articles Coggan suggested and listen to the Real Coaching podcast on this topic