That's bad, Ian -- I'm really sorry for you. Your wife's right, though -- if it's happened this time it can happen easily enough again. But, happily, there's a lot you can do. In the end, the obvious stuff is true. What matters is the muscles: the skeleton comes second. If you've got your muscles strong and flexible (the two don't always go together) you'll be OK. And the other thing is to warm up and -- most important -- warm down. I still remember one incredibly painful back muscle pull I got when I played a game of squash and then stepped into a car for a trip. Surprise, eh? So, if you come in from exercise, get changed (wet clothing will cool you down too fast) and make sure you do a bit of stretching. Best of all, have a hot bath. But, in the meantime, get better soon!