Work on your posture, balance and core strength while sitting in your favorite chair with the FitBALL Seating Disc from Ball Dynamics. This 15in inflatable disc forces you to engage your core muscles while seated, which provides you with extended core training at home or work. The FitBALL Seating Disc can also be used as a balance disc while working out. Use it when doing push-ups or sit-ups for increased muscle training.