To do this exercise you will need a mat and a large physioball. Start by bearing weight on your hands with your shins on the large ball. Inhale to prepare and then exhale as you bend your knees and lift your belly to bend your spine. This will bring your knees underneath you. Inhale as you lengthen your legs away from you, and then exhale as you repeat.
Things to think about
Think of this exercise as a much more challenging version of the cat/cow in a quadruped position. To the flexion of the spine we are simply adding movement of the lower legs.
Make sure you remember that your head is technically part of your spine in the alignment sense. When you are bending your spine, you are also dropping the crown of your head to the ground.