Starting Position: Sit on the stability ball holding each dumbbell with your thumbs wrapped around the handles and your feet flat on the floor. Slowly begin walking your feet forward as you tuck your tail under, lowering your spine onto the ball as you walk your feet away from the ball until your head, shoulders and upper back are resting on the ball. Feet should be parallel and shoulder width apart. Knees are bent to about 90 degrees with your thighs and torso at or nearly parallel to the floor. Distribute your weight evenly through your feet.
Pull your shoulders down and back until you feel your shoulder blades hugging the ball. Position the dumbbells near your chest and armpits with your palms facing forward. Keep the wrist in a neutral position (straight, not bent).
Upward Phase: Exhale, engage your abdominal/core muscles ("bracing") to stabilize your spine. Slowly press the dumbbells upward to a position directly above your chest with your elbows straight but not locked. Your hands should be shoulder-width apart and wrists neutral (straight, not bent). Keep your feet pressed into the floor and your hips pushed up towards the ceiling to maintain stability and control during the exercise.
Downward Phase: Inhale and slowly lower the dumbbells until they are level with or near your chest. Imagine that a bar connects the dumbbells. Try to keep the dumbbells parallel with each other and wrists in neutral position. Your head, shoulders and upper back should be resting on the ball, and your torso and thighs should be parallel with the floor at all times.
During the upward phase, avoid the tendency to thrust your hips upwards and arch your back. Your torso and hips should remain strong and parallel with the floor throughout the exercise.