Electrical stimulation uses an electrical current to cause a single muscle or a group of muscles to contract. By placing electrodes on the skin in various locations the physical therapist can recruit the appropriate muscle fibers. Contracting the muscle via electrical stimulation helps strengthen the affected muscle. The physical therapist can change the current setting to allow for a forceful or gentle muscle contraction. Along with increasing muscle strength, the contraction of the muscle also promotes blood supply to the area that assists in healing.
A TENS unit stands for transcutaneous electrical nerve stimulation. It is a small battery operated machine that uses electrical transmission to decrease pain. Electrodes are applied to the affected area. The machine is turned on and an electrical current is sent through the electrodes. A tingling sensation is felt in the underlying skin and muscle. This signal disrupts the pain signal that is being sent from the affected area to the surrounding nerves. By breaking this signal, the patient experiences less pain.
Transcutaneous electrical nerve stimulation (TENS) is one of the most commonly used forms of electrostimulation for pain relief. Numerous clinical reports exist regarding the use of TENS for conditions such as low back pain, myofascial and arthritic pain, neurogenic pain, and postsurgical pain. The method of pain reduction produced by TENS is explained by the gate control theory proposed by Melzack and Wall in 1965. The "gate" between the level of the spinal cord and the pain centers of the brain usually is closed, thereby inhibiting constant nociceptive transmission by way of C fibers from the periphery to the T cell.
When painful peripheral stimulation does occur, the information carried by C fibers reaches the T cells and opens the gate, allowing pain transmission centrally to the thalamus and cortex, where it is interpreted as pain. Recall that the gate control theory postulated a mechanism by which the gate is closed again, preventing further central transmission of the nociceptive information to the cortex. The proposed mechanism for closing the gate is inhibition of the C-fiber nociception by impulses in activated myelinated fibers (eMedicine Clinical Knowledge Base, 1996; Gersh, 1992; Noback,1991).
A TENS unit consists of one or more electric signal generators, a battery, and a set of electrodes. The units are small and programmable, and the generators can deliver uninterrupted forms of stimuli with variable current strengths, pulse rates, and pulse widths. The preferred waveform is biphasic, which helps avoid the electrolytic and iontophoretic effects of a unidirectional current. A variety of newer transcutaneous or percutaneous electrical stimulation modalities are emerging as technology advances (Jarzem, 2005).