Xiaomi has got several partners especially under its ecological products category and one of such is Yunmai. The company is best known for the Smart Weighing scale which has been one of the rapid selling products released under Xiaomi’s crowdfunding platform. Yunmai has just launched an exercise Powerball which comes with a 69 Yuan (~$10) price tag.
Powerball is perfect for the rehabilitation of Repetitive Strain Injuries (RSIs), Sprains, Breaks & Fractures and general wrist strengthening. The device is also useful for the treatment of wrist pain and other conditions that affect the wrist. The device is purely mechanical and does not need any power, neither will any electromagnetic radiation be produced. The use also extends to merely relieving stress and strengthening of the muscle around the hands. 
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The Powerball has a rotor, also called green wheel, which spins on its axis creating resistance against the user. This resistance is created by the rotor as you turn your wrists which is known as gyroscopic precision. The faster the rotor spins the more resistance there is to the user’s hand. This resistance is purely isometric which makes it ideal for rehabilitation, exercise and wrist pain relief. The shell of the Yunmai wrist exercise Powerball is made of polycarbonate material with a built-in aluminium alloy plating core. It is highly stable and will not crack since the part of the structure of the boot has been optimized to promote smoother and lower noise. In addition, it has a built-in automatic elastic device as well as an array of light which comes on as the device spins.
(source)
