Just came back from Chicago and this is what I see!? HRE, I thought we talked about just letting this thread go...???
Dr. Jtupper: that is a very interesting research. It is quite amazing how much human body can adjust to. You see a fit young man (and nowadays, quite a few fit "old" people as well) who runs and/or bike and/or swim and/or do whatever else comes to their mind and they will go on and do all sorts of activities at home and at work and they seem to have endless resource of energy. On the other hand, you also see some unfit, and quite often obese, people who start to sweat and breath heavily watching TV! Surely it's not how much daily activiy they engage themselves into; but how much the body can handle. Naturally, a trained body seems to be able to handle a heck of a lot more and they don't think anything of it.
One of the reason why Lydiard came up with longer days / shorter days pattern, as well as recognizing how longer runs developed better muscular endurance, was because they tap into different energy system. You might want to run a bit faster one day but shorter duration; and the next day you go further but at easier effort. The way Ray Puckett explained to me was "one day you work hard on your breathing and the next day you go far to spend time on your feet." They are different stresses; and consequently you are giving 48 hours for the body to recover from one set of stress. I'm not sure if this is scientifcally correct but it makes sense to me.
However, for the base building phase, as long as you cover big aerobic mileage without breaking down, it probably doesn't matter that much how you do it. Henry Rono can tap in here but I believe he used to do pretty much the same distance work day after day after day (something like 8 miles in AM and 8 miles in PM) except for Sunday when he went one longer run of about 22 miles or so.