The TKO® stability disc is ideal for developing balance and stabilization. It measures 13" in diameter and is perfect for push-ups and standing, kneeling and sitting exercises.
I bought this to use as a seat cushion at work. I have troubles with occasional back cramps and stiffness, but can not use a ball chair at work. This was a happy compromise. Only complaint is that is a bit small. The 15" version would work better.