Over the weekend, I had an opportunity to visit with my friend, Leslie, and her husband. Her husband noted that Leslie, who is in her late 40s and who regularly instructs exercise classes, no longer qualifies as a ninja because her joints crack when she moves, thus alerting those around to her presence.

I can empathize. I have always had joints that would periodically crack, but now it seems that everything creaks regularly, especially when I get up in the morning. I also find that I feel a...