For those of you like me...with weight that prevents them from running on a treadmill at an early stage of fitness, I received a good tip that has helped me begin to build endurance without sacrificing my knees as I begin.
I do a 45 minute treadmill workout that begins the speed at 2.5 and with a starting incline of 0%. Every five minutes, I nudge the incline up 1%. So during the first five minutes, it is at 0%...the second five minutes it is at 1%...the third five minutes at 3% and so on. If you are doing it correctly, minutes 40-45 should be done at 8%.
I find it allows a gradual workout that is manageable at the start, and easy to adjust as your cardio begins to improve. Eventually, you can bump the speed up, or begin the workout at a steeper incline.
It has definitely been a good starting point for me. It is particularly good at the end of an exercise routine. I will work out with weights or other exercises, and then use the incline routine to finish. Hope this helps someone!