The Pearl Violet PTP CoreBall features a 55 cm diameter, which makes it suitable for individuals between 140 cm (4 ft 7) and 165 cm (5 ft 4). Specifically designed to develop your core strength, balance and coordination, the PTP CoreBall will help you improve your back muscle imbalances and maintain a healthy posture. Exercising on the CoreBall will stimulate your motor reflexes and force your body to react as an integrated system, providing you with a more beneficial dynamic exercise movement. As your body tries to remain stable on the CoreBall, you will be able to engage your abdominal muscles and back muscles more efficiently.