My long post was trying to say most of the details regarding your training will likely have very little impact in the end. If you follow the broad principles that nearly all training plans incorporate you should do about as well as you can given the intensity of your training. I know it took me way too long to say that! Back to too long a discussion: Basically, there are two ways to discover if something works in sports training. The first, easiest, clearest and often best is a NIH sponsored large scale double blind study. Those, alas, are few and far between. But when they do come out they are worth paying attention to. The second is to let competitive pressures do their work. If something works, top athletes are all eventually forced to adopt it to remain competitive. (Even things that have long run negative consequences like steroid use.) If something does not it will eventually fall out of favor. (For example, training so hard every day you nearly drop dead prior to falling asleep each night.) So, an easy principle to follow is make sure your training plan includes whatever the "typical" one does. That is all I wanted to really get across. A quick story: Advice from experts can violate the above principles and when they do I would ignore the "expert." Here is an example from Pfitz's book that I am pulling out simply because I am more familiar with his plan than any other. If you look at his schedule you will see very few MP runs. Why? My reading is that he believes MP runs are too slow to help either with your V02 max or LT but fast enough to dramatically increase the chance of injury. That sounds very reasonable. But is it true? I suspect not. From what I can tell training plans are becoming more and more likely to include MP runs of various sorts, as well as more and more of them. Some, it seems, have you do them almost every week! So it appears that competitive pressures are pushing coaches to move uniformly in this direction. That strongly suggests MP runs, and perhaps a lot of them, are likely a good idea. So, during my next marathon training cycle you can bet I will add in far more than Pfitz suggests doing.