Here is a commercial treadmill developed to give you a challenging workout indoors. The NordicTrack X32i Incline Treadmill comes with a 32 inch HD touchscreen display for interactive workouts. It has -6 to 40% incline control and max speed of 12mph.
This treadmill is smart enough to auto adjust to keep you in your target heart rate zone. It has a 22 x 65″ running belt and max user capacity of 300 pounds. The X32i has sled push grips for intense cardio training. It has dual AutoBreeze fans to keep you cool.