Wrist Trainer Ball Auto-Start Gyroscopic Forearm Exerciser Gyro Ball for Strengthen Arms, Fingers, Bones and MusclesSelf starting designThe movement in the ball comes with a spring starting device, no power supply and no rope. Gently press the inner ball with both thumbs and wind it fully in the direction of the arrow. Then, you can easily start the ball by rotating your wrist in a single hand. Power controlAfter the gyro ball is started, the speed of the wrist movement varies to produce different training forces. Increase the fun of exercise. Mechanical power