Lie on your back with your legs straight and feet and lower legs supported on an exercise ball.
Lift your pelvis off the ground until your shoulders, hips, and feet are in a straight line.
Keeping your trunk stable, curl the ball towards your hips.
Your heels should stay together and your knees should fall outward during this curl motion (frog position).
In a controlled manner, straighten your legs and then allow your hips to move back to the floor, returning to the starting position.
