Mid-section strength and strength endurance are key to skiing performance and skier durability. EO's are a 3-in-1 exercise, training flexion, isometric, and rotational core strength.
Lay on your back with your feet off the ground and knees bent. Move yourself across the floor horizontally by stepping first with your butt, then following with your shoulders. Make 10 steps in one direction, then 10 steps back.