Having wittered on about knees earlier in the week, I tried a few bike rides of about 3 miles and found some reduction in the soreness. After a cautious check this morning, I decided to go to the parkrun on the basis that I didn't have to start (since there is no registration) and, if I did, I could drop out without being noticed. I could also walk a bit if I did try to do the whole thing. With these provisos, I took my place among the pushchairs (actually only one today and no dogs) and set off, seeing the leaders disappearing into the far distance for their 15-16 minute jog. My first km was completed at 7 minutes something/km, giving rise to the wild idea that my overall time would start with 3. It didn't, of course, but I got to the end without walking in 41 minutes, about 3/4 min less slow than the last time. I actually overtook someone younger than myself (they all are anyway). So the said knees are a bit fragile but still working, with caution. Thanks everyone for the advice, which I may turn to again in the next week.