21-mile run: final long run and now the "taper"

Saturday I put in my longest run this year, 21 miles along Alameda Creek in Fremont. This was a very flat run and mostly on dirt trails. It was overcast most of the morning and cool, perfect for our longest training run.
I was a little apprehensive going into this run since I was feeling pretty beat up from the previous week's workouts. As it turned out it was fine. I ran with Jim and Nina from the LMJ&S most of the way. Jim and I ran the first 19-20 miles at a pace between 9:18 and 9:36 minutes per mile. Nina kept up with us for the first 12 miles and then settled into a slightly slower (and more appropriate for her) pace. Nina's a trooper - she's going to do great - she just jumps right into to these challenging runs without hesitation. Great job Nina!
Myself, I hit the wall at right around 20 miles and slowed down significantly for the last mile - maybe 10:30 pace or so. Jim still seemed to be in good shape and continued on at a good clip. Jim has been training longer than I and putting lots more mileage. I often hit a wall at the very end of our longest runs while he just powers on, hence my nickname for him, "The Energizer Bunny". He's going to do great in the Marathon. I'm confident about the first 20 miles, my hope is that I'm able to keep up with Jim in the final 6 miles...
I purposely ate less on this run than I will in the Marathon, forcing my body to convert fat stores for fuel for that last mile or so. It makes for tough running, but I'm hoping a will benefit in the Marathon.
If you haven't run distances of 16 to 20 miles or more, there is a physiological difference from running shorter distances. It's always a challenge to run longer than you have previously, but with distances of 16-20 or more, your muscles run out of Glycogen and your body then has to depend on converting fat stores for fuel. This is much less efficient and so most people experience a dramatic amount of fatigue. That's what occurring when Marathon runners hit the notorious "wall". My intention was to force my body to burn fat stores for fuel instead of allowing it to consume carbohydrates from an energy gel. One of the goals in Marathon training is to get your body more efficient at converting fat stores. I probably consumed about 70 calories from part of a Clif bar on this run, during the Marathon I expect to consume more like 400 calories from energy gels in the final 2/3 of the event. Hopefully, I'll experience fatigue late in the main event, but not hit a dramatic wall with miles to go. You can read more about "the wall" on wikipedia:

http://en.wikipedia.org/wiki/Marathon_(sport)#Glycogen_and_.22the_wall.22

I had a few concerning aches show up late in this run. The shoes I ran in are about worn out and probably weren't the right shoes anyway. I picked up a new pair of running shoes that I'll train in for the next few weeks, and race in if there are no problems. My legs are typically hurting towards the end of these long runs. Hopefully I won't run into any serious problems in the later stages of the Marathon.

All and all I'm pleased with how my training has gone. I'm definitly stronger than a month or two ago and relatively injury-free. I'm happy with how this run went, particularly since I didn't feel rested and fully recovered at the start. I now have 3 weeks of the "taper" period and then the race on August 3rd. The taper is the period before the Marathon where one reduces their mileage and rests up for the race. 3 weeks seems like a long time, but pretty standard. Ok, that's it for now...
More to come!