Electrical stimulators work similarly to the nervous system -- in both cases, an electrical signal causes a specific muscle to contract. A key difference is that the body generates electrical signals internally, while electrical stimulators generate the electrical signal outside of the body. Electrical stimulation units must be approved by the U.S. Food and Drug Administration before they can be sold to the public and are typically very safe if used properly. The devices are not completely without risk, however.
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Interference With Implanted Medical Devices
If you use an implanted medical device that is electrically powered, such as a pacemaker, use caution when applying electrical muscle stimulation. Although implanted medical devices are designed to work properly around other electronic devices, it is still possible for their function to be altered by electromagnetic interference, or EMI, from muscle stimulators. Implanted pacemakers and heart defibrillators can mistake EMI from the electrical muscle stimulator for a physiological signal coming from the body itself. This causes the devices to respond to the signal -- pacemakers do so by changing their rate, and implanted defibrillators may deliver an unnecessary shock.
Research published in the "European Journal of Applied Physiology" in 2011 shows that certain types of muscle injury can be caused by electrical muscle stimulation if the tissue becomes too tense during the electrically induced contraction. Muscles are most easily injured at the musculotendinous junction and can tear at these sites if the stimulator is turned up too high. Electrical stimulation can also cause pre-existing muscle injuries, such as tears and deep bruises, to get worse and may even prevent full tissue healing. If a muscle begins to hurt more when stimulation is applied, turn off the machine and consult a medical provider for guidance on appropriate parameters.
Improper use of a muscle stimulation unit can easily lead to skin burns, according to research published in "The Journal of Arthroplasty" in 2005. Dr. Daryl Lawson states that if a strong electrical current is delivered through a small electrode, the skin is exposed to a higher concentration of electricity per unit of area, which can cause burns. Be wary of skin pain and discomfort at the area under the electrode during stimulation. While stimulation often causes a strong tingling sensation, it should not be painful or cause distress of any sort. If the stimulation is painful, turn off the machine and remove the electrodes so your skin can recover.
According to Bioness, a manufacturer of electrical stimulation units, skin irritation can occur because of a reaction to the electrode adhesive or the electrical current itself. To help prevent a reaction to the adhesive used on electrodes, the company recommends thoroughly cleaning and drying the skin before applying the electrodes. Areas of skin that you have recently shaved may also be more prone to being irritated and inflamed by the flow of the electric current. If you have continued skin irritation even after taking precautions, seek guidance from a medical professional.