The reason I asked was because it actually felt quite good, in a slightly masochistic sort of way. I didnt run it particularly hard and it felt like I'd done a 13-15 miler at steady pace. Also, at present my running is fairly limited i.e. 2-3 times a week or so 3 mile stretches to 10-12 mile steadys to simply be used to running for that distance/time, plus runs in fells of 3-5 hours plus. I think with the amount I do, any run has to be off some benifit. But as people are saying its a matter of degree. I was, to some degree, under the impression that if you ran back to back hard efforts that was benificial and that would be basically running the second day tired to some degree. It seems to be a basic philosophy amongst ultra running.