Finally the proof I needed!!! Stability balls are crap!!

(from the Journal of Strength, Conditioning Research)
Stability balls less effective than power lifts for building core strength.
Go to almost any gym in North America and you'll find a wide variety of exercise balls, balance discs and wobble boards, bosu balls that are used to build core stability. The core muscle act like a corset around the spine to provide stability for lower and upper-body movements. For example squatting on Bosu balls(ball with flat surface on the bottom ) requires activation of the core so that you can maintain balance and preform the exercise.
Unfortunatley, training on unstable surfaces decreases the capacity to lift heavier weight. Consequently, stability training decreases the capacity to strengthen major muscle groups.
James Nuzzo and collegues from Appalachian State University in North Carolina found that common stability ball exercise were less effective than deadlifts or squats for activating core muscles such as rectus abdominus, obliques, and back extensors. They concluded that stability ball training do not provide sufficient overload to increase stength and hypertrophy, and questioned their value in a exercise program.