Interesting and enlightening article on Washington Post.com…
I can certainly attest to the “…there are some huge differences — physiological, logistical and psychological — between running far and running really, really far.” quote…and I’ve only checked off the 50K and 50-miler distances!
Read more…
DENNARR(dot)COM 
I read this and thought it was interesting– I didn’t realize the extent of how ultras could potentially harm you (compared to marathon running). Thanks for sharing!