“When I can’t get to the sea water or to a tennis court, or out for a long, brisk walk, I work on stretch exercises at home. One that I do many times a day as I move around my apartment involves standing for a moment with my back again a wall. I dig my heels into the floor, stand straight, and place the palm of my hand between the small of my back and the wall. Keeping my chin level, I pull the crown of my head toward the ceiling. At the same time I push the small of my back toward the wall until there’s no longer room for my hand.”