Well, oh dear oh dear oh dear. Actually, the graph has maintained quite an impressive mountainous shape - it's the lack of horizontal growth that's been the problem recently, as I've only put in five new entries this month (having started this whole routine off doing three a week, making about twelve).
After finding that I could run at 5.2mph fairly comfortably, I decided to try to get myself up to 6mph so that I could run a mile in ten minutes. I stepped up to 5.4, which was all right, and then to 5.7, and wondered aloud if people could just... keep training themselves to keep going up, and what the limit was on that. Well, it turns out I do have a limit, and I think it's 5.2.
I thought I was building myself up quite well, though I only managed twelve straight minutes the first time I got to 5.7 and then fifteen the next time. The third time, I was able to complete nine minutes before my right knee insisted that it would be unwise to continue - I stopped, alternated walking and jogging a little more gently for a while, then stopped comfortably and got to the door of the gym before it suddenly decided to take a break from its vital support role and I fell over sideways.
The following week, I had a couple of sessions that I didn't even record because I couldn't continue after a few minutes - my lungs are fine and I would only be comfortably out of breath at the end of a session, but my legs would give out long before then. So I've reverted back to the slower running speed at which I was going before, and the last couple of successful sessions have been fairly constant at 300 calories in either completely constant running or with a break in the middle of only about one and a half minutes. The knee still tends to complain a lot afterwards, but I have a knee brace now, and I'll have to see what running in that is like...
I weigh 170 pounds exactly.