You can truly appreciate walking and running on a treadmill.
Intensity is determined by the speed and elevation settings.
You can either control the settings yourself through the manual mode or experiment with the preprogrammed workouts. Many home models will allow you to program your own workouts and keep them in memory as a preprogrammed workout. Your heart rate will go up quickly in response to even slight elevation changes such as I to 2 percent. Do not focus so much on heart rate that you forget about your muscles, which may not be used to elevation. Elevate gradually and give your muscles time to adjust.