Which is a bummer.
I honestly thought everything was going to be OK. I felt good. I had even survived a dog incident one and half miles in, involving a mad retriever who kept jumping up at me, leaving me with some fetching, bleeding welts that were sore not only with the friction of running, but sweat made them sting.
As I ran away I came up with a great speech to give the stupid owner about controlling her dog, but all I managed at the time was 'THAT HURT!' said firmly to her face as I ran past.
I got 9 miles out, and sped up a little as there were then some downhill sections, and felt great. Last week, at 15 miles, I could not have gone a step further, but today, I still felt quite human, but at 16, then wheels suddenly came off. It amazes me how quickly that can happen and how unpredictable these things are (See David's post on marathons for further details)
I jogged on until 17 miles, then stopped my Garmin, and started to walk. After a little while I felt looser, and tried to start up again, but my knee went mental on me. It actually proper hurt, not just a niggle.
The other annoying thing was part of the railway was still snowy, some was muddy, and a section has been covered with a coarse sandy stuff that went into my shoes and was hard going to run on.
However, after a bath, I felt far better than I did this time last week.
I even did some hoovering, whereas last week I just laid on the sofa, thinking I was going to puke, so there is some improvement.