Small, precisely timed electrical pulses are sent to the nerve supplying the target muscle. These pulses act as a message, telling the muscle fibers to ‘contract’. The muscle fibers contract in much the same way as if the message had come from the brain.
Whereas in conventional muscle contraction signals are sent from the motor cortex area of the brain. These signals travel down along the spinal cord. Signals go to the intended muscle by means of the peripheral nervous system. Once at the muscle, the signals result in muscle activation/contraction.
We just by-pass the brain and spinal cord and send the signals to the nerves directly over the muscle! Signals are sent via the gel pads. Signals activate the nerves. Nerves switch on the muscles.
EMS results in the same end result as working out in the gym – muscle activation! The premise being, if you activate a muscle strongly enough, enough times, over a sufficient training period the end result will be a muscle training effect.