55cm JumpUSA Exercise Ball with free pump included (The diameter of ball will measure 55 cm before it is inflated.). Core strength training is the only way to exercise. You can take your exercise balls with you wherever you go or exercise at the convenience of your home. Ideal for stretching, strengthening and toning exercises. First used by physical therapists over 30 years ago, Exercise Balls are now used in leading health clubs around the nation and are quickly becoming a standard item for any home gym. The JumpUSA Exercise Ball is safe, durable, and easy-to-use.