Core Balance Stability Trainer by Harbinger Highly versatile, the Harbinger Core Balance Trainer can be used in a variety of exercises to enhance core muscle strength and development, as well as improve balance and posture. This compact, inflated disk is two sided - smooth and nibbed - to use on different training surfaces. You'll be amazed by its multiple uses and effectiveness. Core Balance Stability Trainer Features: Anti-burst, can withstand 500 pounds of pressure, and can be re-inflated using standard bicycle pump and pump adapter Enhances core muscle strength and development by isolating specific muscle groups Can be used standing, sitting, kneeling, lying down, and in tandem with exercise equipment such as balls or resistance cables Made of soft, pliable PVC with a nibbed surface on one side, and a smooth surface on the other 13 inches in diameter and 3 inches in height