Constance Alexander: From fit to spry in the blink of an eye — but assuring you, Paul McCartney lives

Two good habits, maybe three, are all I can boast: Wearing a seat belt, not smoking, and maintaining a regular regimen of jogging. Since these practices are part of my routine, I don’t think about them much. Up until last Friday, in fact, I considered myself reasonably fit. But now that has changed. Please let me explain. It was an annual wellness visit, and I was chatting with the health care professional...