I  followed the good advice I got from several veteran marathoners on active.com about not doing long runs too fast - the purpose is to build endurance rather than speed/stamina. After last week's 15.6 mi "speed session" (so to speak), I did three days of crosstraining and then went back out to run. The short run was 4.5 mi @10:30 pace, which was probably slower than I needed to do for that distance. However, I wanted to feel the pace and also needed an easy run. Then more crosstraining and then the long run, which was 16.6 mi @10:18 pace. I thought I was doing about 11 min/mi, but when I mapped it, found I was faster than I'd thought. Guess I can thank my 10K background for that. But my legs felt much better after the 16.6 mi than they did last week after the 15.6 mi. They were very tired and needed some stretching, but they didn't feel like they'd been run over by a truck. The slower pace (10:18/mi rather than 9:41/mi) made a big difference. Also I showered my legs with cool water for a few min after the run - since I don't yet have the nerve to get in an ice bath. The cool water felt great.