Electrical muscle stimulation

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 electrotherapy and of muscle training. It is cited by important authors as complementary technique for sport training, and there is published research on the results obtained. In the United States, EMS devices are regulated by the U.S. Food and Drug Administration (FDA).

History
Luigi Galvani (1791) provided the first scientific evidence that current can activate muscle. During the 19th and 20th century researchers studied and documented the exact electrical properties that generate muscle movement. It was discovered that the body functions induced by electrical stimulation caused long-term changes in the muscles. In the '60s Soviet sport scientists applied EMS in the training of elite athletes, claiming 40% force gains. In the '70s these studies were shared during conferences with the Western sport establishments. However, results were conflicting, perhaps because the mechanisms in which EMS acted was poorly understood. Recent medical physiology research pinpointed the mechanisms by which electrical stimulation causes adaptation of cells of muscles, blood vessels  and nerves.

Theory
EMS causes adaptation, i.e. training, of muscle fibers. Because of the characteristics of skeletal muscle fibers, different types of fibers can be activated to differing degrees by different types of EMS, and the modifications induced depend on the pattern of EMS activity. These patterns, referred to as protocols or programs, will cause a different response from contraction of different fiber types. Some programs will improve fatigue resistance, i.e. endurance, others will increase force production.

Use
EMS can be used both as a training  and a therapeutic  tool.

In medicine EMS is used for rehabilitation purposes, for instance in Physical therapy in the prevention of disuse muscle atrophy which can occur for example after musculoskeletal injuries, such as damage to bones, joints, muscles, ligaments and tendons. However, this should not be confused with TENS (Transcutaneous Electrical Nerve Stimulator): the use of electric current in pain therapy.

Because of the effect that strengthened and toned muscles have on appearance (a stronger muscle has larger cross-section ), EMS is also used by a niche of practitioners for aesthetics goals. The FDA rejects certification of devices that claim weight reduction. EMS devices cause a calorie burning that is marginal at best: calories are burnt in significant amount only when most of the body is involved in physical exercise: several muscles, the heart and the respiratory system are all engaged at once. In general, spot reduction of fat deposits by exercising only a few muscles underneath, voluntarily or electrically, does not work.

In EMS training few muscular groups are targeted at the same time, for specific training goals. The effectiveness of the devices for sport training has been debated. A niche of coaches regularly use professional EMS devices as integral part of the training of their athletes; some of these are high profile coaches, such as track coach Charlie Francis, who used the technique to supplement the training of Olympic-level athletes. Non-professional devices target home-market consumers with wearable units in which EMS circuitry is contained in belt-like garments (ab toning belts) or other clothing items.

FDA certification
The U.S. Food and Drug Administration (FDA) certifies and releases EMS devices into two broad categories: over-the counter devices (OTC), and prescription devices. OTC devices are marketable only for muscle toning; prescription devices can only be purchased with a medical prescription for therapy and should be used under supervision of an authorized practitioner, for the following uses: The FDA mandates that manuals prominently display contraindication, warnings, precautions and adverse reactions, including: no use for wearer of pacemaker; no use on vital parts, such as carotid sinus nerves, across the chest, or across the brain; caution in the use during pregnancy, menstruation, and other particular conditions that may be affected by muscle contractions; potential adverse effects include skin irritations and burns
 * Relaxation of muscle spasms;
 * Prevention or retardation of disuse atrophy;
 * Increasing local blood circulation;
 * Muscle re-education;
 * Immediate post-surgical stimulation of calf muscles to prevent venous thrombosis;
 * Maintaining or increasing range of motion.

Only FDA-certified devices can be lawfully sold in the US without medical prescription. These can be found at the corresponding FDA webpage for certified devices. The FTC has cracked down on consumer EMS devices that made unsubstantiated claims; many have been removed from the market, some have obtained FDA certification.