The 65cm two-tone Reebok Gymball is one of the most versatile pieces of exercise equipment for improved all-round fitness, used to perform a wide variety of exercises which will considerably improve your core strength, posture and flexibility. Its weighted base provides additional grip and helps to stop the ball rolling away during every type of exercise. Though they may appear the same, gymballs come in many diametrical sizes and materials, so it's important to choose the right exercise ball for you.