EMS stands for Electrical Muscle Stimulation
A device generates safe impulses that are sent through electrodes to your muscles. These impulses cause your muscles to contract - just like they do during natural 
movement. The key difference is that EMS activates more muscle fibers than traditional exercise.
Sessions are short, but highly effective. A 20-minute EMS workout can engage the same muscles as 2 hours in the gym. More efficient training - more efficient results.
 

 During traditional strength training the brain sends impulses which stimulate certain muscles to contract. However, not all muscles have a well-developed connection to the brain and these muscles are not activated as easily and therefore they will not 
develop so well. 

EMS Training stimulates all the major muscle groups and also helps to develop the motoric nerve connections relating to muscle movement. By sending electric impulses directly to these motoric nerves, even the weakly connected muscles are activated. 

EMS training is a completely safe form of working out and as such,it has been used for medical and rehabilitation purposes for a long time. 

The EMS device is able to achieve what the human brain cannot. 
Electric muscle stimulation (EMS) induces muscle contraction with the help of electric current. Such contraction is different from the one induced in traditional training controlled by the central nervous system. 
The nature and intensity of the stimulus depends on the parameters configurated on the device. 
Electric impulse provides the tools for engaging the muscles. This impulse is transmitted from the EMS device through the neurons and motoneurons to the muscles. Its role is to induce muscle motion.