Last night was the last test before the Marathon, to confirm that the pace I want to go out at is realistic. In other words, that I am not going to accumulate lactic acid in my muscles. This isn't the only thing that can scupper a Marathon but at least it is something relatively easy to measure.
The test involved running a kilometer round the tartan track at a prescribed pace (I had to make sure I passed the little cones set apart every 100 meters every time my watch beeped) and then my pulse was read and a drop of blood was extracted from my ear to measure the amount of lactate that had accumulated.
I did the first two kilometers in 4:15 (just under sub 3 hour Marathon pace) and the last two in 4:00. My pulse rate for the first two was 155 at the end and, for the second two, was 166. I have to wait to hear the verdict from the lactate analysis, but it looked like it was very low (and constant, i.e., not accumulating) at the pace of 4:15. (I just got the results: 1.7 mmol at 4:15 per km and 2.9 mmol at 4:00 per km. As expected, my pace should be somewhere between the two but closer to 4:15. Here is a good article on the subject.)
My coach was there and said that the question wasn't whether to go at sub 3 hour pace but rather to risk going for an even faster time. Unless the results say otherwise I aim to stick to the plan I laid out recently: run to the pulse rate set out by Jonathan, at which I have never blown up (touch wood) and, at which, I have achieved several personal best times.