I ran about 35 miles per week training for my first marathon, which was this past Jan 1st. I had leg cramps the last 3 miles, but was able to go on a long walk withy wife later that day. Two days later I was back running, but a week later after a 12 miler I felt some knee pain (beginning of IT), so I spent a week on the stationary trainer. I ran the 2nd marathon 6 weeks after the first, and lowered my time by 5 minutes, running out of gas at mile 24. The third marathon was a month later. I primarily did speed work to get ready. At mile 20, the knee began to hurt again, so I walked the last quarter. Oh well.
All this is to say that you can try and do whatever you want, but if you try to train through pain, you will fail. You HAVE to get healthy before training.
Know where your problem points are, and if you feel a twinge, give it a week of rest.
Finally, if you PR your half during a full, may God have mercy on your soul. Don't do that. Some really good runners have pulled that crap. On that day they were fools. If you are wired to do that sort of crap, don't listen to yourself. Just don't.
For my PR, I hit my target pace for the first time at mile 10, spent the next 10 miles tracking down "lost" time, and the last 2 giving some of it back (out of gas).
94chem,
That, sir, was the greatest post in the history of TexAgs. I salute you. -- Dough