Here is a quick run down on your VOLT workings.
The JetBlack VOLT™ EMS Smart Trainer uses an electromagnetic system to apply resistance. An electric current level is calculated and applied to an impermanent magnet to generate an electromagnetic field. The electromagnetic field exerts an electromagnetic force on the magnet, which provides resistance to the VOLT trainer in turn applying resistance to the user. This electromagnetic magnet system provides resistance over the conventional gravitational force used in free weights. Other forms of resistance systems used in bike trainers are wind, magnet (non-electrical) and fluid.