During the past week, I've been thinking about the soreness in my right leg and knee. A week ago when I ran fast and caused the problem, I wasn't going any faster than I did in running my last two 5K races, and I had no problems after those runs. The only thing that I can think of that makes sense is that my leg & thigh muscles are weaker than they were at the time of the two races.
Prior to my fast run last week, I had gone through two weeks of a lot of walking but no running. That might have allowed my muscles to deteriorate. Perhaps more important, I had been getting careless in doing my stretches before my runs. Before each run, I try and do the stretches that are shown on my picture page. Included are strengthening exercises for my knees, quads, and thighs. I've been skipping those exercises on quite a few of my runs, and that might have allowed my muscles to become weaker. I'm going to be more consistent in doing those exercises. Plus, as soon as I get a bench set up in my basement, I will start doing the resistance-training exercises shown on my total-body page. Hopefully, with a stronger body, I won't have problems with my speed runs.