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Make sure you are securely planted on the ball before proceeding. Squeeze the ball by bringing your calves closer together as you rest your arms at your sides. Tighten your abs and relax your head and neck, pressing your lower back into the ground. You should now be in a neutral position for this exercise.

Summary:
Set your exercise ball in a vacated area. Lie down with your back against the ground and your legs straightened out in front of you with one leg on either side of the exercise ball.