Starting Position: Lie prone (on your stomach) over the top of a properly-inflated stability ball (one that compresses approximately 6" under your body weight) with both feet and hands on the floor, hip- and shoulder-width apart.
Gently contract your abdominal/core muscles to stiffen your torso and slowly walk yourself backwards until your stomach lies directly over the top of the ball with both legs extended and both feet firmly placed on the floor, hip-width or wider apart. Your head, torso and legs should be in parallel alignment with your arms resting on the ball.
Place your hands to the sides of the ball close to the top, positioning your hands directly under your shoulders and elbows by your side. Think about trying to squeeze the ball between your hands to create more strength and stability.
Upward Phase: Exhale and slowly press your body upwards until your elbows are fully extended, but not locked. Maintain your head, torso and leg alignment, and elbows by your sides. Hold this position briefly.
Downward Phase: Inhale and gently lower yourself to your starting position.
Exercise Variation (1): If this body position proves too difficult in pressing upwards or in stabilizing your torso, take yourself down to a kneeling position, aligning your head, torso and thighs throughout the exercise.
Exercise Variation (2) : To increase the balance challenge, this exercise can be performed by bringing your feet together behind you and raising one foot off the floor.