Winner Space Wincspace Wrist Trainer Powerball Arm Strengthener Essential Gyroscopic Wrist and Forearm Exerciser Ball (Red) Strengthen fingers, wrists, hands, forearms, shoulders and bicep etc., and also be beneficial in promoting co-ordination and blood circulation. Rehabilitates sore muscles and joint, great for musicians, guitarists, pianists, drummers. Small, compact and transportable, you can take anywhere. Simple to start with a pull-string. All you need do is to increase the speed by making a rotational wrist movement and to keep in sync with the spinning of the ball.Powerful and High performance rotor with up to 12,000 RPM The faster you spin the harder your muscles work.