Wirst sports crazy ball Wrist ball with NEON&counter Increase strength of fingers,wrists,hands,forearms, biceps,triceps OEM There is no any battery or electricity inside the device.It is application by centrifugal force & inertia like a gyroscope. It is powered by rotating the wrist. The speed of rotation can reach over 12,000 RPM.TheoryLike gyroscopes.centrifugal force and inertia are applied. ...