The Core Stability Ball is a fun, yet challenging way to stretch, tone and tighten your body. Unlike training on a stable, flat surface, the ball is a round, unstable surface, so you not only train the primary muscle groups, but also the smaller stabilizing muscles - primarily used for balance, alignment and posture. The ball should be large enough so that when you sit on it, your knees bend at a 90-degree angle. The 55cm ball is recommended for most people 5' to 5'5". This kit includes a ball pump, 2 ball plugs, an easy-to-follow exercise wall poster and a 25-minute workout DVD.

Sizes S (55 cm), M (65 cm) and L (75 cm)