Challenge the deepest stabilizing muscles in your body while exercising on the unstable base of this 55cm (22) Stability Ball. Designed to improve balance and strength as well as tone your body, this Stability Ball is also used as an office chair. Safety tested under 250kg (550lbs) of pressure. Sold individually, this Stability Ball is ideal for those under 170cm (5 3) tall. Includes BONUS Exercise Guide!