Open Leg Rocker is a challenging exercise for many different reasons. It requires core strength and control as well as a mobile spine, flexible hamstrings and a stable shoulder girdle. Many classical mat exercises lead you up to Open Leg Rocker including; Spine Stretch Forward and Rolling Like a Ball. A way to modify Open Leg Rocker is to practice with bent knees holding on to the outside of your shins. Then gradually work up to straightening your legs.