This morning during a yawn, I arched my back into a stretch. You've probably done this yourself. You know, one of those stretches with arms raised and shoulders back. Anyway, while doing this, I felt a stabbing pain in my back, like someone had thrust a knife into my left lung. Movement was difficult for a few seconds. Though I eventually recovered a nearly full range of motion, a knot of dull pain remains in that area of my back.
So I have now reached the age that I need to do warm up stretches before I stretch.