What is Electric Muscle Stimulation?
Electrical muscle stimulation (EMS), also known as neuromuscular electrical stimulation (NMES) or electromyostimulation, is the elicitation of muscle contraction using electric impulses. EMS has received increasing attention in recent years due to its versatility. It has the potential to serve as a strength training tool for healthy subjects and athletes, a rehabilitation and preventive tool for partially or totally immobilized patients, a testing tool for evaluating the neural and/or muscular function in vivo, and a post-exercise recovery tool for athletes. 
The impulses are generated by a device and delivered through electrodes on the skin in direct proximity to the muscles to be stimulated.  The impulses mimic the action potential coming from the central nervous system, causing the muscles to contract. Sports scientists have cited EMS  as a complementary technique for sports training and published research is available on the results obtained.  In the United States, EMS devices are regulated by the U.S. Food and Drug Administration(FDA).