• Discomfort during treatment.
• Skin irritation at the site of electrodes.
• Worsening spasticity.
• Strained muscles.

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.

However, some authors imply that EMS can lead to exercise since people toning their muscles with electrical stimulation are more likely afterwards to participate in sporting activities as the body becomes ready, fit, willing and able to take on physical activity.

“Strength training by NMES does promote neural and muscular adaptations that are complementary to the well-known effects of voluntary resistance training”. This statement is part of the editorial summary of a 2010 world congress of researchers on the subject. Additional studies on practical applications, which came after that congress, pointed out important factors that make the difference between effective and ineffective EMS.

This in retrospect explains why in the past some researchers and practitioners obtained results that others could not reproduce. Also, as published by reputable universities, 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. Some important considerations prior for the use of NMES are to make sure there are no present bone fractures, burns, skin lesions, lupus erythematosus, thromboembolic disease, deep vein thrombosis Luigi Galvani (1761) provided the first scientific evidence that current can activate muscle.

During the 19th and 20th centuries, 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 1960s, Soviet sport scientists applied EMS in the training of elite athletes, claiming 40% force gains. In the 1970s, these studies were shared during conferences with the Western sport establishments.

However, results were conflicting, perhaps because the mechanisms in which EMS acted were poorly understood. Medical physiology research pinpointed the mechanisms by which electrical stimulation causes adaptation of cells of muscles, blood vessels and nerves.

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 be purchased only with a medical prescription for therapy. Prescription devices should be used under the supervision of an authorized practitioner, for the following uses:

• 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.

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

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.