Start in 4 point with your hands under your shoulders and knees under your hips and your spine in neutral spine. Begin to flex your spine by simultaneously tucking your chin towards your chest, pushing your upper back up to the ceiling and tilting your pelvis backwards (imagine tucking your tailbone between your legs.) Once you have gone as far as you can go without pain hold for a few seconds. Start to extend your spine by simultaneously untucking your chin and looking up to the ceiling, letting your rib cage sink down to the floor and tilting your pelvis forward (imagine pushing your tail bone up to the ceiling.) Once you have gone as far as you can without pain hold for a few seconds then return to your neutral spine position. Repeat, each time you should be able to get a little more movement.