It is application by centrifugal force & inertia like a gyroscope. Dynamic There is no any battery or electricity inside the device, it is powered by rotating the wrist, and the speed of rotation can reach over 12..000R.P.M FUNCTION 1. Perfect exercise gadget for sports like golf, tennis, squash, cricket, badminton, baseball, bowling, basket-ball,, motocross, mountain climbing, 2. Increases strength in fingers, wrists, hands, forearms, biceps, triceps, ligament and shoulders 3. Great benefit for musicians, guitarists, pianists, drummers, 4. Rehabilitates sore muscles and joints.