Crimminy, my knees ache just reading this article. If you have ever tried to backpack a long distance in a single day either out of necessity or (as some do here) for "fun", well, I think you could identify with the effort necessary to accomplish such a feat.
Honestly, could I do 48 miles in a day? I've done 35 in the Sierra, so I would think yes, there might be one day in me when I could do 48 given the right preparation and terrain (assuming 16 hours of walking). Could I do two back-to-back. Heck, no.
That's what makes these things so impressive. It's not the daily miles as much as it is the repetitious nature of those miles.
Thanks for posting this!