If we look at the original failure model, and then we look at the changes that were made to that model when periodization came along and took things to another level, one of the things that jumps out was that there was an increased time spent in comfort during periodization.
With periodization they changed the loading parameters every so many weeks, and cycled different intensities, changed the exercises. All of which essentially allowed people to extend training time spent going to failure because as the CNS became burnt out from going to failure in one way, several things got changed and allowed it to continue going to failure in other ways for a while (similar to rotating the exercises every couple of weeks during the max effort days in the Westside model).
Then we look at intensity cycling. Again there was an increased time spent training in comfort because the sets didn’t go to failure for most of the cycle. They were maybe using five reps the whole way, but they started off doing five reps with a weight that they could probably do 10 or 15 with. This allowed the central nervous system to begin to trust these weights, and trust this movement pattern and thus allowed for an increase in their neurological efficiency around said movements. Which ultimately allows us to use more and more of what was already there to begin with in terms of potential muscular innervation (read..strength).
Cycling weights in this way meant that by the time they came to what was previously their limit, their central nervous system had already decided to allow them to go further, and use more of what was already there. Or to be able to use less of what was already predetermined to get the same job done. It really doesn’t matter to the outcome which was which… different process, same result.
So, with each progressively better strength programming ethos the there was an increased time spent in comfort. What is the common denominator then of improved ideas when it comes to acquiring strength? Increased time spent training in a relative comfort zone.
An ever expanding comfort zone if you will.