Electrical muscle stimulation, or EMS, is the use of electrical impulses to cause muscles to contract. EMS has long been used in physical therapy, and research has shown that it can help strengthen and tone muscles, though only to a certain extent. However, manufacturers' claims that EMS devices promote weight loss or fat loss have never been proven.
Function
EMS works by simulating the natural process of exercising muscles. When you want to move your arm, for example, your brain sends electrical impulses down the spinal cord and out through nerve pathways to reach the proper muscles for the job. Those impulses stimulate the muscles, causing them to contract, and your arm moves just like you wanted it to. With EMS, however, the impulses come from electrodes attached to the skin over the muscle, not from your brain. The electrodes deliver impulses--tiny electric shocks, really--and the muscles contract.
Benefits
Doctors and physical therapists regularly use EMS to treat people who have suffered a loss of muscle function, such as from a stroke, spinal cord injury or other nerve damage, or who are unable to exercise certain muscles because of injury or surgery. Because EMS simulates natural muscle activity--muscles contract when the impulses are applied and relax when they aren't--it can help maintain tone and strength in muscles that would otherwise "atrophy," or waste away from lack of use. Another common use of EMS is to relieve muscle spasms.
Misconceptions
A misconception about EMS, and the basis for many of the weight-loss claims surrounding it, is that since it mimics natural muscle movement, it will produce the same effects as a workout. Exercise is really nothing but repeated cycles of muscles contracting and relaxing, whether it's your arms lifting weights, your legs carrying you along on a run or your "abs" doing crunches. As your muscles work, your body burns calories to keep them going, and that's why exercise helps you lose weight. However, when you undergo EMS, the energy to move your muscles isn't coming from your body; it's coming from the EMS device. Your muscle cells may be getting a nice little workout, which may help their tone, but you aren't burning the calories you would with a workout.
Warning
According to the Food and Drug Administration, which regulates EMS devices, there is no evidence to back up claims that EMS "belts" and other wearable devices sold to consumers produce advertised benefits such as "rock-hard abs," a firmer body or drastic fat loss. A study by researchers at the University of Wisconsin-LaCrosse came to a similar conclusion--even when used exactly as directed, stimulators didn't have any effect on appearance.
Expert Insight
Fabio Comana, an exercise physiologist, tells Fitness magazine that EMS's supposed effects on appearance are rooted in the "spot reduction" myth--the idea that working a particular area of the body will reduce fat in that area. No matter how well-toned your abdominal muscles may be, for example, you aren't going to have "six-pack abs" if there's a layer of fat on top of them. The only way to reduce fat is with diet and cardiovascular exercise. And you can't pick where the fat comes off, either. That's determined by genetics.
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