A ring shaped structure having a ring shaped inner channel, and a ball which is located inside the ring shaped structure and which rolls in the ring shaped channel. The ring shaped structure may be comprised of a first ring shaped structure and a second ring shaped structure which are attached together to form the ring shaped structure. The ring shaped structure may have an inner diameter； and the apparatus may further include a handle which spans the inner diameter of the ring shaped structure. The apparatus may further include a first attachment device； and a second attachment device； wherein the first attachment device connects to the second attachment device inside of the handle to attach the first ring shaped structure to the second ring shaped structure. The apparatus may include a device for measuring movement of the ball. The device for measuring movement of the ball includes an accelerometer.
