Unlike other therapeutic modalities presented in this text, electromyographic biofeedback does not deliver energy to the body. Instead, biofeedback measures the amount of a specific type of physiological activity that is occurring. In the case of muscle contractions, the amount of motor nerve activity is being observed. The biofeedback unit then converts this activity into a visual or audible form that can be interpreted by the patient and clinician.
• Biofeedback is the process of detecting physiological activity in the body and converting that activity into visual and/or auditory cues that the patient can use. With electromyographic (EMG) biofeedback, the unit amplifies the body's neuromuscular electrical activity and converts it to auditory and/or visual signals. The patient then uses this feedback to modify further activity such as increasing muscle contraction.
Consider, for example, a patient who is recovering from anterior cruciate ligament (ACL) surgery who is unable to voluntarily contract the vastus medialis oblique (VMO) muscle. Because of swelling, lack of use (disuse atrophy), and pain, the patient does not contract this muscle. With time, the normal neurological loop used to innervate the VMO is lost; the patient "forgets" how to contract the muscle. When biofeedback is used over the VMO, the feedback indicates when motor nerve impulses are being directed to the muscle (Fig. 18-1).
Electromyographic Biofeedback. Electrode placement for the vastus medialis oblique muscle.
Biofeedback measures at least one of five biophysical properties (Table 18-1). The resulting feedback can be used to reeducate muscle, facilitate muscular relaxation, control blood pressure and heart rate, and decrease the physical signs of emotional stress.
TABLE 18-1Types of Biofeedback ||Download (.pdf) TABLE 18-1 Types of Biofeedback
|TYPE ||PRINCIPLE |
|Electromyographic (EMG) ||Measures the electrical activity in skeletal muscle. |
|Mechanomyographic ||Measures the transverse displacement of the skin over the target muscle based on the sound produced and/or skin tension. Quantifies oscillations in skin caused by changes in muscle fibers.179 |
|Peripheral temperature ||Measures temperature changes in the distal extremities (e.g., fingers). |
| ||Increased temperature indicates a relaxed state (increased superficial blood flow). |
| ||Decreased temperature indicates stress, fear, or anxiety (decreased superficial blood flow). |
|Photoplethysmography ||Measures the amount of light reflected by subcutaneous tissues based on the amount of blood flow. |
|Galvanic skin response ||Measures the amount of perspiration on the skin by passing a small current through the fingers and/or palm. Sweaty skin contains salt and is a better conductor than dry skin. |
Biofeedback does not monitor the actual response itself (e.g., the strength of the contraction), but rather it measures the conditions associated with response (e.g., neurological activity). The normal proprioceptive input is amplified through the use of sound, light, or meters. The strength of the feedback increases as ...