Powerballs

NSD Powerballs are finely engineered, precision crafted gyros consisting of a rapidly spinning rotor enclosed in a solid [hand held] outer sphere.

You set this rotor in motion using a cord or your finger and build its speed by subtle rotation of the wrist. It contains no motor or batteries. All of the energy required to spin the gyro is generated by the user.

The faster you spin the inner rotor the more inertia it generates and the more resistance it subsequently inflicts upon the fingers, hands, wrists, arms and shoulders. The stronger you are, the faster you will be able to make your NSD Powerball spin. Most models have electronic counters built in which will allow you to see how fast you managed to spin the rotor (and keep a record of your progress).