Several years ago, I noticed a disturbing and encouraging pattern to my running: between 12 and 20 miles, I hit the wall. This is regardless of the length of the run. After coming to the realization, its reality set in, and I have found that every run comes with a built in "wall" between 12 and 20 miles. The problem is not so much the wall, but the fact that it lasts from, well, mile 12 to mile 20.
I take electrolytes. I consume them by the handful. More precisely: 1 tablet every 15 minutes to begin. By hour 2: 1 tablet every 12 minutes. By hour 4: 2 tablets every 8 minutes.
Once I hit mile 20, things change. The cramps leave, strength is renewed, and it's like I just started running. But getting to mile 20 is like ... well, it's bad.
So, if I could make any suggestion to race rules: could there be an allowance for a pacer between miles 12 and 20? Yes, I need another at mile 70. But at least the last few runs/races, it's getting to mile 20 that's the hardest.