As silly as this sounds or looks, this is a great alternative to actual running outdoors if you happen to injure your knee or foot while running. A year ago, I slightly injured my left knee, and the coach recommended that I aqua jog. I put one of those belts on and jumped in the deep end. I simulated my run as if I was really running outside. I "ran" for a duration for 2 hours, but here's the drawback... BORING! Better than sitting on your ass being injured though!

Just in case you feel like doing a little exercise in the pool.