.....I used to run a lot. Back in the day we didn't have the great shoes that are available now. My back reminds me of it everyday, now.
I got into swimming instead which is not always convenient (or comfortable jumping into the water initially). It can be harder to fit into a busy schedule (some days, it just isn't possible), but it was surprising to me when I started how flexible the options were ( I don't have a reliable time in my schedule that I can count on each day; but on the other hand, I am up a lot at nonstandard times anyways which means an empty pool like this AM.
I highly recommend it for anyone who knows how to swim and can find a way to do it - it is a GREAT work out without any of the wear and tear which is a big deal down the road. The only downside is that whole "breathing oxygen thing".