http://www.amazon.com/TKO-3038-38-Inch-Mini-Trampoline/dp/B000WSIJYEI got one of these off craigslist, and it's been such a godsend. I have hip and leg trouble, and I know if I tried running or conventional aerobics on a hard surface I'd just ruin my joints. On one of these trampolines, though, I just grab a 3lb weight in each hand(for better balance, not the weight), put on some music I like, and jog in place for 15-20 minutes. I don't jump on it, just jog. I started with 5 minutes and I recommend starting light and working up as you feel comfortable. You get a more intense workout than you think you will. My heartbeat is just racing after 20 minutes. I want to up the time to 30 minutes twice a day. Doing this exercise shaved a hundred points off my blood sugar reading(I have type 2 diabetes) within 45 minutes of finishing.