Lie on the ground and breathe freely, As you exhale flatten your body on the ground push yourself into the ground. Notice how and where you tense up to do this and relax. Now breathe and tense up and note where your body moves up or down and how the changes form rests on the ground. Play with different body parts and indevidual muscles to find out what form and ressistance they supply and than start to move on the ground as you repeat this drill rolling from side to side and overhead. This drill comes to help you become aware to your own tension and release muscle tension that comes from fear of body injury. You still need some fear from the ground in your head to keep you from being cocky and get hurt as the systema guidebook states and you will get this if you work honestly on changing surfaces.