Here is another compact treadmill that gives you a solid workout indoors. The Wonder Maxi Under Desk Treadmill has a shock absorbing running belt and 1.75HP motor. It lets you walk or run at speeds up from 1 to 6km/h.
This under desk treadmill measures 55.3″ x 22.8″ x 4.6″. It weighs only 58.4 lbs, so you can move it around or put it under your bed without a whole lot of effort. A safety key is available to prevent accidents.