[header] How to do russian twists [title] Place a mat or towel on the floor. [step] Place the mat near a couch or another piece of furniture that has a small, but big enough, space to stick your feet under. The resistance from the couch will stabilize your body while you do the twists. 
Lie down on the mat with your knees bent and place your feet under the couch. [substeps] Alternatively, you can have a friend hold your feet down for you instead of the couch.