NR, I'd love to be able to
NR, I'd love to be able to run 6 miles on gravel. That's quite an accomplishment.
My barefoot running goal for the year is to "master" rough surfaces. At least 5 miles in every direction from where I live, nearly all streets that can be run on are chip seal. And nearly all the sidewalks in this area are old (at least 50 years), so are highly eroded and often rougher than chip seal.
Earlier this spring, I was running 1-3 miles on these rough surfaces at 10-11 minutes/mile. (On smoother pavement, I run 8-9 minutes/mile and on a rubber/artificial track I run about 7 minutes/mile.) I took 1-2 days off in between, but my feet got increasingly sensitive, raw, and feeling "bruised" (although not actually bruised).
After reading Ken Bob's book (which is worth its weight in gold, even if you've read everything on his web site), I've tried to rededicate myself to bending my knees. Really, it's like sitting (Ken Bob's Groucho Marx stance/drill helps a lot, I think). Gordon Pirie, the British track and cross country great from the 1950s, once noted that even though he was taller than most of his competitors, when he ran, he was about 1/2 a foot shorter than them, because he was sitting so low (that is, bending his knees).
I've also tried to re-emphasize relaxing my feet. The way I noticed I wasn't relaxing is when I was running on a rough sidewalk once. I ran across a few "new" concrete squares that were smooth and my feet flattened comfortably on the surface (like a few seconds of relief). Then a couple of steps later, I was back on the rough sidewalk, and my feet tensed up, almost contracting, and it was more uncomfortable. I have to consciously try to relax and not anticipate discomfort. It's sort of like taking little leaps of faith that it's not going to be as bad as I think it might.
So now I am running 1-2 miles on the same surfaces, but even slower (12-13 minutes per mile). My feet are recovering better between runs (still 1-2 days in between). And I'm trying to walk for a few minutes on sharp gravel before running. The contrast is great -- it makes chip seal seem like silk. And there have been moments that the chip seal even feels good (although more moments when it doesn't feel so good!).