Electrical muscle stimulation (EMS), also known as neuromuscular electrical stimulation (NMES) or electromyostimulation, is the elicitation of muscle contraction using electric impulses. 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. The electrodes are generally pads that adhere to the skin. EMS is both a form of electro therapy and of muscle training.
The machine is good as others have said for retraining muscles that have experienced some sort of atrophy like Lee's did when he was laid up with that broken back of his... laying round for weeks or even months at a time can lead to atrophy and so the muscles tend to forget what they're supposed to be doing.... in a sense. But understand the movie didn't show much of his own rehabilitation beyond that machine... he busted his *** to get back into shape and being stronger than before... that superb physique of his was from long hard dedicated work.
Building up muscle mass requires the tearing of muscle fibers in the area desired, small tears when the muscles are stretched out to their present limits and are rebuilt when they grow back but instead of shrinking the muscle tissue grows towards the broken/torn ends and thereby over time... builds mass... Or didn't you know that already?
Understanding HOW the body works, grows, repairs itself really goes a long way in getting the kind of body you want... understanding how exercise machines work and what they offer helps in getting the RIGHT equipment instead of some gimmick device that really doesn't do anything than put money in the inventor's pocket.
Find a good reputable body builder in your area (there's at least a dozen serious knowledgeable ones in every town/city) and ask them how to and find a regime that works best for you.
It does exist but I have not tried it. Those that have displayed some levels of progress with it. They actually have one you can purchase off t.v. for your abs... basically... it fires electricity into muscles to increase the rate of expansion and contraction thereby working them out temendously without the physical workout dynamics...