Starting Position: Lie on your back on a mat, placing the backs of your lower legs and heels on the top of a stability ball. Your feet should be lined up with your hips and your toes pulled slightly toward the ceiling. Gently contract your abdominal/core muscles to flatten your low back into the floor. Try to hold this gentle contraction throughout the exercise. Extend your arms out to your sides with palms turned to the floor to help stabilize your body during the exercise.
Gently exhale. Keeping the abdominals engaged, lift your hips up off the floor. Press the backs of your lower legs and heels into the ball for additional stability. Do not lift the hips so high that the low back begins to arch. Your abdominal contraction will also help avoid excessive arching in the low back. Continue to press upwards until your body is in a straight line from your heels to your shoulder blades.
Upward Phase: Exhale. Slowly bend your knees and pull the ball toward your hips until you can rest the soles of the your feet on top of the ball. Your toes may point away from your body in this movement. The hips will continue to lift as you pull the ball toward your hips. Keep the torso stable.
Lowering Phase: Inhale. Slowly press the ball away from your hips until the knees are straight, stabilizing with the core, hamstrings, glutes and arms. Repeat for a prescribed number of repetitions and slowly lower yourself back towards your starting position.
Exercise Variation (1): To increase the balance challenge, move your feet closer together on the stability ball.
Exercise Variation (2): To increase the balance challenge, move your arms towards your side or place them on your chest to reduce your stabilizing points of contact with the floor.
Exercise Variation (3): To increase the balance challenge, raise one leg off the ball in the starting position and curl with one leg.
Avoid arching your lower back as your press your hips upward to the starting position. This can be achieved by contracting your abdominal muscles prior to lifting and keeping them engaged throughout the lift.