I've already mentioned that a week or so after the Woodside 50k I went to the track and couldn't run faster than 6:27/mile. This was a wakeup call that my mix of training needs to change and focus more on speed. But a few weeks after this I ran 37 miles and pretty much beat any fast twitch fibers out of my legs.
This last saturday we were visiting Laguna Beach and I ran 10 hilly miles in 1:20:00 in the morning. Then I ran 8 hilly miles in the same time with a fast finish in the afternoon with Scott White. I'm not advocating dropping long runs over 20 miles but limiting the slogfest 5+ hour runs and alternating tempo 20+ mile runs one weekend with a double day of the same mileage would make for better recovery and not limit fast twitch muscle recruitment.