I stopped after the 12k run today at Blackwater Duathlon. Those folks were tough and fast - at 1 mile into the run (that I hit at 9:59) the other women looked like they were all a half mile or more in front of me! (Only I and one other woman finished the first 12k at a pace slower than 10 min/mile).
It was just too freaking hot for my state of fitness. I couldn't keep my heart rate under 170 and still jog. Too early in the day to race with a higher heart rate than 170, with 40 miles on the bike and 5 miles in the run yet to go. I had to keep dropping to a walk to get the heart rate under control. Started gettting goosebumps. I finished 12k in 1:23 (12:22 min/mile) with each mile dramatically slower than the last (plots to follow if I download them from my Garmin). I found my bike was the VERY LAST in T1. It actually started to go a little bit dark for a moment there in T1.
I figured that I'd have to walk most of the second run in order to finish. I just didn't have the gumption to want to walk the second run for 5 miles.
Instead I opted to ride my bike out (after I recovered a little) and work the last aid station during the run instead. I had MUCH more fun, and helped the other death marchers make it home.
I might have qualified for the World Championships if I had finished - there were only 3 finishers in my division. (And I hear the duathlon World Championships course in Richmond this year is pretty hilly and brutal.)
But that's racing. There's always next year!