The colourful light bar inside the ball changes colour as the speed of the core increases, making it more fun to exercise. Self-starting without the fuss, no need for traditional pull cords, just follow the arrows and push to the end to release the ball centre to start. The wrist ball is mechanically powered and requires no power source. The centrifugal force generated by the interaction between the wrist rotation and the internal rotating core keeps the core rotating at high speed. A special wrist strap must be worn to prevent the ball from spinning out too fast due to excessive force. Effective for relieving musculoskeletal pain and strain caused by prolonged use of the wrists and arms, and also for strength training for the fitness enthusiast. This metal wrist power ball has a built-in automatic bouncing mechanism that can be easily activated with a push and release, and can be controlled for added entertainment and fun with a variable speed light to experience the power of impact. Description: This metal wrist ball has a built-in automatic bouncing mechanism that can be easily activated with a push and release, and can be controlled for added entertainment and fun. The wrist ball is mechanically powered and requires no power supply. The centrifugal force generated by the interaction between the wrist rotation and the internal rotating core keeps the core rotating at high speed. It can be used to relieve musculoskeletal pain and strain caused by prolonged use of the wrist and arm, and can also be used for strength training. A special wrist strap must be worn to prevent the ball from spinning out too fast due to excessive force. The colourful light changes with the speed of the ball, making it more fun to exercise. Specifications: Core material: Zinc alloy Shell material: Polycarbonate silicone Colour:Black Size: 70*70*55mm Package Including 1*Wrist ball with light