Surface Electromyography (SEMG) – A Diagnostic Tool
SEMG is a clinical tool used by chiropractors in the treatment of aberrant joint movement, musculoskeletal pain, and some neurological disorders.
Surface EMG may be used to better understand how a fixated joint is causing a broader problem; it allows one to see how the mobilization of a joint has allowed the muscles to reorganize themselves. When used as at training tool, one can teach the patient how to use their body and/or muscles differently so that the joint fixation won’t replicate itself in the future.
In conditions which involve chronic pain, antalgic postures may readily be identified. Surface EMG can help find the tension in a reputed tension headache; the source of such pain can reside at a distance from the site of reported pain. Potential perpetuating factors associated with myofascial pain disorders may be described, and the SEMG feedback to the patient as part of the retraining process.
Surface electromyography can provide Chiropractors the information necessary to evaluate and follow pain sufferers with muscle impairments, as well as to establish selective treatment protocols in a scientific manner. It is well known that muscular tension maintains a substantial role in the development of the pain-spasm circuit, which can be treated using techniques of self-regulation in the form of biofeedback. Traditionally, biofeedback has been associated with relaxation training as a means to lower the emotional arousal component involved in pain.
The development of “static muscle scanning” techniques in the 1980s (Cram and Steger, 1983) better allowed the practitioner to precisely map areas of chronic asymmetric muscle tension, better describing one of the characteristic of the pain syndromes. In addition, studies of the recruitment patterns (amplitude and timing) of selected muscles may show asymmetries of muscle function amongst synergists and antagonists, providing a stronger description of how pain creates and is associated with disordered movement patterns. Both the static and dynamic sEMG findings can serve as landmarks for potential biofeedback assisted relaxation or muscle retraining sites, thus enhancing the efficacy of these endeavours.
The clinical use of SEMG in the assessment of pain related disorders was originally introduced by Edmund Jacobson in the 1930 as he began to study the effect of imagination on a variety of muscles. Janet Price, in 1948, utilized multi-site recording procedures and noted that muscle bracing patterns associated with chronic pain seemed to be asymmetrical, and eventually migrated to areas other than those of the original site of pain. Later, George Whatmore (1974) one of the students of Edmund Jacobson saw disease as resulting from “dysponesis” or inappropriate muscular efforts. He conceptualized EMG activation patterns from the point of view excessive bracing, the over-representation of emotional events, inefficient movements, or inappropriate attentional efforts.
Basmajian and Wolf were one of the first teams to document a specific neuromuscular deficit in low back pain patients. Here, they noted the lack of a “flexion relaxation” response in the erector spinae muscles of back pain patients. More recently, the work of DeLuca and his colleagues has focused on changes in the energy spectrum of the muscles in back pain patients. Using spectral technique, they have noted that these individuals tend to demonstrate a higher level of muscle fatigue than compared to normal data.
Surface EMG represents the summation of all of the alpha motor unit activity which reaches the recording electrodes. Typically, the electrodes are placed close together and the recording area is relatively small and specific. Rather than considering these recordings as representing innervations from specific nerve roots, it is more appropriate to think of this activity in terms of motor or muscle function. Such function is organized at multiple levels, including a segmental level.
Also, one should consider the dynamic interplay between the excitation associated with muscle spindle activity versus the inhibitory influences of the golgi tendon organ. The gamma motor system modulates much of the sensitivity of this interaction and is partially regulated by the cerebellum. It is also excited by nocioception. These afferent fibers give rise to an excitatory push on the gamma motor system, providing the basis for “muscle splinting” around the injured area or joint. This may also modulate posture, potentially leading to learned alpha and gamma motor behavior and antalgic postures. If this postural adjustment is maintained over an extended period of time, trigger points as well as changes in the resting lengths of muscles will ensue. The patient will eventually learn to move differently, usually restricting his or her movement, while substituting inappropriate muscle groups. Lastly, the pain patient may experience changes in emotional tone associated with pain. Recent evidence has demonstrated that the muscle spindle is activated by ANS activity associated with stress. Fear of pain may increase the resting tone in the muscle due to increased sympathetic tone.
In addition, the patient may become anxious about their pain and avoidant behavior patterns may develop. Problems of learned disuse of injured muscles or muscles associated with an injured or fixated joint, may need to be addressed. All of the above described changes in muscle function associated with pain can be documented using surface electromyographic techniques.
Cram JR and Kasman GS. (1998). Introduction to Surface EMG, Aspen Publishing, Gathersburg, PA.
Donaldson S, Clasby B, Skubick D and Cram JR. (1994). The evaluation of trigger point activity using dynamic sEMG techniques, American Journal of Pain Management, 4:3, 118-122.
Kasman G, Cram JR and Wolf S. (1998). Clinical Applications in Surface EMG, Aspen Publishers, Gaithersburg, MD.
Have a great weekend,
Dr. Crysta Serné
Vancouver Chiropractor and owner of Vitality Clinic
What To Expect During Your First Chiropractic Visit