If you've read the running thread you'll see that I am 5'6" and currently weigh around 200 lbs. I haven't weighed this week yet, but sincerely hope that with all the exercise I've done that I'll finally be back in the 100s. In any case, I've been running now for about 2 months. It's all been on the treadmill at the gym until this past Sunday when I ran/walked about 5 miles outside. It was a big change, but I feel great that I did it. If you are in good shape physically you should be able to walk/run without too much difficulty. It's not easy, but the benefits will be worth it for you! An overused NIKE ad - Just Do It! comes to mind...