The ProSource Core Balance Disc is a small but useful tool to help train your core, tone muscle, and improve your posture. The unstable surface requires your body to engage all of your core muscles, resulting in better balance and overall strength. The inflation amount can be adjusted for less or greater sturdiness, depending on your workout need, and the non-slip grip surface prevents slipping. Comes with a pump, making it easy to inflate and deflate. Manual is available for download in Product Details section.