This yellow Gymnic Classic Exercise Ball is 450mm (17.75\") in diameter and the ideal aid for helping to strengthen and tone a user\'s abdominal and trunk muscles, and the arms and legs.This inflatable vinyl exercise ball also provides excellent therapy for perceptual motor training activity, especially for children with abnormal reflex patterns, or for general exercises and group activities. Gymnic Classic Exercise Balls are high quality, durable, exercise balls that have a strong seamless construction that allows them to withstand rugged use by both adults and children, and are available in a range of different diameter sized therapy balls, all of which are available in this area of our shop. Please note the exercise ball is supplied deflated and will require inflation prior to use.