While scientists have debating for years about the cause of the extinction of the dinosaurs and their cretaceous cohorts, I think I can solve the riddle of my dead legs a bit more easily: poor planning and overtraining. I'm running the Philadelphia Marathon in late November. I have absolutely zero interest in long runs during the hottest part of the summer, but I've been trying to build my base up by increasing the length of my regular runs to improve my overall weekly mileage.
I've succeeded; my 38 miles last week was my 2nd best ever, eclipsed only by the week in late February where I did my 18-miler as a last-ditch attempt to "catch up" as much as possible on my long runs in my ITBS-hampered Shamrock marathon training. I'd only had one other week since March where I'd been over 30 miles, a week in April where we had beautiful weather and I got 2 10-milers in (and another the following week).

Those had been my only 10-mile runs since the marathon; I have 5 in the last two weeks. And, on the last three of those I'd adjusted my route to add some steep hills at the end, in hopes of being more prepared for the supposedly very tough Dreaded Druid Hills 10k on June 25, my thoughts being that since I normally run a hilly route, but probably not as hilly as the race course, I'd run a long enough distance, and add some rougher terrain to be as ready as possible.
My plan was to do today's route again on Saturday, and then next week (probably Monday and Wednesday), run two shorter routes consisting of just running up and down the two steepest hills over and over again. (This route would be like going up and down a half-pipe for several repitions.)
Given that I feel like my legs are fossilized, I think I'll re-evaluate. I'm going to take tomorrow off, run 6ish miles on these two hills on Saturday, and then do a mini taper for the rest of next week. I've also got fairly low expectations. If this course is as tough as I've heard, I don't think I'll really be racing it. Ok, I mean, it's a race and I'll be in it, but there's no thoughts of a PR here.
My 10K PR is 59:32, and it should be my easiest PR to break. I've only run one 10K race, in which I paced myself conservatively having never run six miles, and I routinely come in 2-5 minutes under that on my regular runs, and occasionally hit the 10k mark in the 52-minute range. At Druid Hills, though, I'm just going to have fun, keep a slow and steady pace that I can maintain up the inclines, and try to not get caught by the T-Rex.