Maintainable Base Fitness (MBF) explained

I've decided to describe what i'm trying to achieve with the acronym MBF which stands for Maintainable Base Fitness.  MBF describes the maximum fitness an individual can achieve using a training schedule that is maintainable indefinitely.  No periodization.  No offseason.  No peaks and valleys.  Any MBF is bound to be pretty low volume - most people keeping track of their training over a period of years would find that even something considered very low volume (in the ultra endurance world) such as 6 hours a week is not sustainable in the long term.  Traditional IM training?  forget about it. 


The idea of what MBF  means is of course open to variation and interpretation.  Different people might look at developing an MBF  for a  period of a single year, several years, or be aiming at a decades long approach, which I am the most interested in exploring.  My journey started some years ago with three hours of weekly training.  But over time i found that even three hours produced psychological stress in my life that i don't want to sustain indefinitely.  When i reduced the load to two hours it still led to some minor mental and motivational issues.  So now i've settled in to one hour a week and so far so good. 


Of course i have big ambitions, and part of what it means for something to be maintainable for me is that it must enable me to challenge those ambitions occasionally.  In other words, it's still gotta get me through that IronMan, that four day adventure race, and allow me to feel age group competitive (which for me is finishing roughly in the top third) in pretty much any event. 


I know many people read this and think that i'm crazy and should settle for less, or perhaps more correctly, that reality will force me to do so.  But i don't want to, and apparently, at least based upon what i've been able to accomplish on 3 or 2 hours a week, reality must be sleeping on the job. 

But the question remains as to whether my MBF on only one hour a week will actually be sufficient given my ambitions.  i'm pretty confident though, and not without reason - i feel as fit, or nearly so, as when i was putting in three times as much time, and succeeding at really big things.