One of the 14 bones I broke over my lifetime was my patella (kneecap) and my ortho suspects that I injured something beneath it as well, because my knee acts up occasionally if do quick, sudden, side to side movements such as in basketball, tennis or raquetball. I haven't played pickle ball, but I have seen others do so and suspect that the movements are similar to the other problematic sports I mentioned. I can run four miles with three screws in my hip or do 100 floors on the Stairmaster at Level 7, and my knee is okay. But often when I do quick or sudden movements in a fitness class, it acts up. Maybe that is what your friends are experiencing? PS: I know, 5 pm was a hard time for me as well (I used to work out at 4:45 a.m. when I was working full time and was raising a young foster child with special needs, so I'd work out early and be back home by 7 to wake him up and get him off to school. I'm definitely a lark, not an owl. But 5 pm was the only time that the classes were offered, so I had to decide if I was going to make a commitment to get stronger bones, rather than letting my skeleton turn to dust. I'm used to it now -- again, the key is not lying down or sitting down in late afternoon when energy starts to fade. I have half a cup of coffee, envision what I will look and feel like in 10 years if I DON'T go (my 95-year-old mother is in a wheelchair due to osteoporosis), and MAKE myself get in the car and go. Once I'm there, I'm okay -- it's always nice to see my comrades in fitness showing up and cheering one another on. None of us is willing to "go gently into that good night"! Rather, as Dylan Thomas would say, we are the ones who will "rage, rage against the dying of the light." Sorry -- the writer in me couldn't resist. ;-}