LOW-VOLTAGE VERSUS HIGH-VOLTAGE CURRENTS

Voltage generators producing 150 volts (V) or less are catergorized as producers of low-voltage current. Although they can cause muscle contractions, these generators are more effective in producing chemical and thermal reactions.

High-voltage therapeutic units, which produce waveforms with amplitudes of more than 150 volts, are highly effective in causing muscle contractions. The high amplitude and short pulse widths allow nonirritating stimulation of both nerves and muscles.

Pulsed Direct Current Muscle Stimulation

The use of pulsed direct current high-voltage stimulation is becoming increasingly popular in sports medicine. New devices are able to stimulate muscles and nerves directly.

Indications
In general, electrical stimulation as therapy for stimulation as therapy for athletes is used to decrease muscle atrophy, decrease swelling, reeducate movement, decrease pain,introduce anti-inflammatory and analgesic drugs through iontophoresis, and localized trigger points.

Application
In electrotherapy, moist electrode pads are fixed directly to the skin. The smaller active pad, which brings the current to the body, can range from very small to 4 inches square; the larger disposal pad, from which the electrodes leave the body, should be as large as possible. Because the current flows between the two pads, the distance between the two pads depends on the type of muscle contraction desired. The closer the pads are, the shallower and more isolated the contraction; the farther apart the pads are, the deeper and more generalized the contraction. The physiological effects can occur anywhere between the two pads, but they usually occur at the active electrode, since current density is greater at this point.

Direct current is mainly used for its ability to reduce pain, reduce edema, stimulate denervated muscle, and perform iontophoresis. Interrupted, or pulsed, high-voltage direct current can stimulate muscle contraction as well as alternating current. This pulsed high-voltage electrical stimulation is becoming the treatment of choice for acute pain, swelling, postoperative pain, and muscle reeducation.

In some cases a tetanizing current has relieved a muscle spasm. A frequency between 30 and 40 pulses/sec will produce tetanus. The tetanizing period should be relieved by a time of relaxation. A ratio of 1 to 3 is desirable, with 10 seconds of contraction followed by 30 seconds of relaxation. The treatment time should range from 15 to 30 minutes, two or three times a day.

Active exercising can be used while the muscles are being electrically stimulated. Electrical stimulation with exercise seems to increase muscle fiber innervation. Other therapies that can be effectively combined with electrical stimulation are ice pack tratments or cold water immersion. Care should be taken not to stimulate muscles immediately after an acute injury or to open wounds or incision sites.

Iontophoresis

Iontophoresis is the precess whereby chemical ions are transported through the intact skin by an electrical current. Using a direct current low-voltage uninterrupted generatkor with positive and negative electrodes, the medication is transported into the body through the positive electrode. The polarity of the electrode used in iontophoresis depends on the polarity of the ion introduced. medications of choice for treating musculoskeletal inflammatory conditions have commonly been pain relievers such as lidocaine (Xylocaine) and anti-inflammatory agents such as hydrocortisone or dexamethasone. Commonly, this treatment approach is for tendonitis, bursitis, myositis, and arthritis,

The anti-flammatory medication and if desired, an analgesic are applied beneath the positive pole.

TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION (TENS)

In recent years, transcutaneous electrical nerve stimulation (TENS) has become popular for treating both acute and chronic pain. This approach stems from Melzack and Wall's gate-control theory of pain. it is theorized that through TENS there is inhibition of spinal cord neurons, direct peripheral blockage of nerve fibers, and activation of endogenous opiates such as endorphins. TENS units are designed to stimulate the afferent sensory nerve fibers, which respond best to a medium frequency of 2 to 150 pulses per second and with a pulse width of 40 to 500 m sec. The TENS unit is commonaly set just below the cite where a muscle contraction is produced.

The electrodes of TENS are placed at trigger points or dermatome sites adjacent to the injury of surical incision. Because TENS does not have to be worn continuously; 1/2 to 1 hour application will often relieve pain hours after it is removed. Another major value of TENS is that it allows pain-free exercise.

Special considerations
As with any modality, electrotherapy, in general, must be conducted with great caution. Protocols for a given stimulation unit and physical condition must be carefully adhered to. When using uninterrupted direct current, tissue damage can occur from excessive current. No stimulator should be placed over the carotid sinus, the abdomen of a pregnant woman, or where there is a pacemaker. When extremitites are treated, the indifferent of dispersive electrodes should be placed on the same extremity and not the thorax to avoid having the current go through the heart.