Principle: Using gyroscope (eccentricity and constant rate of inertia) Power: Power is generated by wrist rotation, no battery or plug-in rotation, the faster the kinetic energy. < p>Function: improve grip, endurance, wrist strength, arm strength and other sharp tools, and can promote blood circulation, strengthen wrist ligaments, and reduce sports injuries Use effects: For those who love golf, bowling, baseball, basketball, volleyball, handball, tennis, badminton, kendo, etc. Various sports players who need to rely on the wrist can make you more powerful and powerful. Those who are engaged in computer typography and piano practice avoid ligament injuries. Workers accustomed to wrists usually need more practice.Rehabilitation function to prevent muscle stiffness. Advantages: The world's smallest ball with the strongest kinetic energy. It is suitable for all ages and is not limited by space. It can be used anytime and anywhere in home activities, watching TV, climbing mountains, going out and in the office. Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement.