Gyroscopic exercise balls are hand-held devices used in therapy and strengthening exercises, primarily to exercise the hand and wrist. are commercially available.

U.S. patent number 3,726,146 from Archie Mishler describes a gyroscopic exercise ball including a rotor which rotates about its spin axis and about a second axis at right angles to the spin axis, which rotor increases in speed by applying a torque about a third axis. This phenom enon is commonly referred to as precession.

Typically, a gyroscopic exercise ball includes a rotor centrally disposed on a shaft within a spherical housing. The housing almost fully encases the rotor except for a small circular opening through which a portion of the rotor extends in order to give the rotor an initial spin about its spin axis. The ends of the shaft are mounted in notches of a lightweight ring, or gimbal, which is disposed in a groove of the housing which circumferentially surrounds the rotor. The groove is wider than the diameter of the ends of the shaft and also allows the lightweight ring to spin therein. In response to an external torque, applied by the wrist, one end of the shaft rolls around the top edge of the groove while the other end rolls around the bottom edge as the lightweight ring rotates, thereby causing the rotor to speed up. As a general rule, the higher the applied torque, the faster the rotor will spin.