Effective pain relief using a tens or an interferential unit only happens when the electrodes are placed to inundate the painful area with a pleasant, tingling, massaging type stimulus. The stimulus is creating nerve firings of NON PAIN FIBERS, sensory fibers, which makes those sensory nerves overpower the PAIN NERVES ( C-FIBERS), which are transmitting the pain stimulus. There is no magic, it's simply a process of understanding what is the purpose of placing the tens electrodes, generally self adhering reusable electrodes, in the proper place.
Unlike acupuncture where the needle is very small, a tens or interferential electrode has a much larger stimulation area and specificity of placement is not as critical. Needles in acupuncture often are intended to interrupt an electrical energy pain path, whereas electrical stimulation is intended to be offensive and invade the area thusly interrupting and altering the electrical energy. The surface of an electrode may be 2 inch x 2 inch or 4 square inches of surface area per electrode equaling a total of 8 sq. inches, where the acupuncture needles surface is that of the needle itself times the depth the needle is inserted.
Acupuncture is a process of finding and insertion into an area a needle(s) whereas electrical stimulation (e-stim) is a process of hovering over and transmitting electrical energy in an area. Interferential has a much greater frequency ( rate-how many times machine goes off and on per second). The higher the rate, the less the resistance is, and the greater the penetration of the electrical stimulus. Acupuncture needles have to be inserted past the point of most resistance ( skin or scar tissue ) to get into the area of electrical energy to interrupt the flow.
The dispersion of the energy with estim and reusable electrodes covers a much larger area and increases the chances of pain stimulus interruption.
Electrode placement is solely about passing electricity between two or four electrodes through the painful area. As the pain moves, which is very common for chronic pain conditions such as osteoarthritis, fibromyalgia, RSD, back pain, radiating sciatica, foot pain, knee pain, joint pain, shoulder pain, RLS -Restless Leg Syndrome, etc., then the electrodes can be repositioned to pass the stimulus through the pain area(s).
Electrodes come in many varied shapes and sizes, from butterfly to oval to rectangular to circular and many more such as skin friendly electrodes. The size of the electrode chosen is done to cover the area being treated. If the pain emanates in the spine and the painful area is 6 inches or so long then often a 1" x 6" electrode will be used, or an Oval electrode, and staggered placement, so the 6 inches per electrode of stimulation surface area (SSA) can be placed to totally stimulate the painful spine area. If the patient has knee pain then a smaller 2" Round electrode may be used to cover the popliteal space behind the knee, which is much smaller, but the stimulation will cover the knee pain area.
Often the two electrodes per channel can be of differing shape and size depending on the severity of the pain in a specific area. This process enables the electrical stimulus to be targeted by intensity, especially when using interferential therapy. Interferential therapy requires larger electrodes due to what is called "current density".
Current density is comparable to one standing in a shower that delivers 10 gallons per minute of water through only one small hole. If the patient is standing a few feet away under that shower head then the single stream of water would be uncomfortable due to the pressure behind the flow. Showering would be a painful process. That is overcome, by rather than one small hole add 100 more to the shower head, and now the sensation of showering is comfortable and possible without pain. With interferential the same principles apply to electrodes. Electrodes larger than typical tens electrodes are used to reduce the current density by increasing the stimulation surface area.
With interferential therapy, due to the 8,000+ rate, electrodes used are generally larger than a typical tens electrode of 2" x 2". Since there is considerable more energy then the dispersement area has to be greater than 4 sq. inches. Interferential therapy also prolongs the life of electrodes because, unlike tens therapy, the brief 20 - 45 minute interferential treatments produce carryover pain relief, and do not require an electrode to be worn continuously. Fewer electrodes are needed for interferential therefore also less cost.
Below is a longer video on electrode placement for both tens treatments and interferential treatments that may be helpful. It's 11 minutes long however we also have a 2+ minute shortened electrode placement version if you prefer.
How To Place Tens Electrodes For Pain Control.
More information is available on interferential by watching the below video on site: