Steady on the ball

... in the 1960s for physical therapy, but have since been used in gym workouts to rev up traditional push-ups, sit-ups or yoga moves. The idea is for the ball's instability to improve a user's own stability, coordination and posture. The same concept ...

http://www.thestar.com.my/Lifestyle/Family/Features/2013/12/27/Steady-on-the-ball.aspx