Challenge the deepest stabilizing muscles in your body while exercising on the unstable base of this 55 cm (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 250 kg (550 lbs) of pressure. Sold individually, this Stability Ball is ideal for those under 170 cm (5’ 3") tall. Includes bonus exercise guide! Ideal for those 4'11 to 5'3" Includes hand pump and bonus downloadable exercise guide Anti-burst up to 550lbs Merrithew 22-in Black Stability Ball with Pump