National Running Day run - endurance, not distance

Today is National Running Day, and I thought I would attempt something new.  Since it was pouring raining, I went to the gym to run on the treadmill.  I decided I try 'running' (more like a 'slog' - slow jog - 4.0 mph - random program, incline 0.0 - 1.5%) without stopping or walking as long as I could.  I got past 5:00 and thought I would push another 5:00 and see how I and my knees felt.  Well, it's 10:00 now, and I was really sweating - but I still felt like I could go another 5:00.  If I could make 15:00, I could check off one of those Tribesports.com challenges.  FINALLY, the clock on the treadmill reached 15:00 - I did it!  I had only traveled 1.0 mi, but the fact that I ran the whole time - not slowing down, or walking, or stopping - was gratifying. Today the goal was endurance, not distance.  So now that I had completed 15:00, certainly I could go 30:00!  I thought I would crank up the speed, but changed my mind - why tamper with perfection (LOL)!  I strode along for another 15:00 and finished with 2.0 mi (257cal; 5:00 cooldown/35:00, 2.17 mi, 281 cal).