Exercise bikes (sometimes referred to as exercise cycles) are good for the large muscle groups in the legs. These bikes are manual and have variable resistance. Some exercise bikes will also work the torso and upper body. A recumbent exercise bike puts less pressure and stress on the back. You can choose from upright exercise bikes which give you the feel of a pedal bike, recumbent exercise bikes where you sit back and pedal putting less strain on your back (good for those who have the room and beginners). Finally commercial exercise bikes can be bought which are designed for those serious about there biking.