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10 Articles in Volume 6, Issue #3
A Muscular Approach to Headache
Adjuvant Analgesia for Management of Chronic Pain
Breakthrough Pain In Non-Cancer Patients
Case Presentation of Munchausen Syndrome
Electroanalgesic Medical Device
On Knowing
Opioid Malabsorption: Can You Stomach This?
Sedation Safety and Comfort
The American Board of Independent Medical Examiners (ABIME)
The Role of MMPI-2 in Assessment of Chronic Pain

A Muscular Approach to Headache

Muscular dysfunction of head muscles —through their range of motion and at rest—may result in headache due to muscle over-exertion and fatigue

The present article presents a novel approach to evaluating the potential contribution of dysfunctional muscles of the head to headache. The analysis is based on dynamic and quantitative surface electromyography (SEMG) of a number of muscles through a range of motions and facial expressions.1 The hypothesis underlying this approach is that muscular fatigue and ensuing pain is generally the result of muscular over-exertion and asymmetry in terms of contra-lateral function.2 This hypothesis is derived from the results of SEMG dynamic protocol studies that will be presented below. The hypothesis may be further supported by the SEMG findings of agonism/antagonism of a number of head muscles. The definition of synergism/agonism and antagonism is derived from the statistical analysis of muscular inter-relations during any given range of motion.3

This electrophysiological modality has a dual application: (1) the investigation of the muscular dysfunction through motion and rest during the classic or functional head & neck ROM, and (2) the muscular re-education of the resting tonus and activity tonus of the dysfunctional muscles.1,4 Both applications can be achieved by utilizing well-established protocols within the framework of the clinical presentation.5

This modality is rather unique in terms of the rehabilitation component: it is active. The healing process noticed peripherally on the head & neck muscles is related to the re-establishment of the neuro-motor engram and the positive neuroplastic process.6,7

Data presented in Tables 1 and 3 below refer exclusively to database studies performed on 569 asymptomatic muscles, involving a total of 21,350 readings. The testing has been conducted with standard SEMG dynamic protocols through the classic ROM of the neck, facial motions, and TMJ motions at the minimal voluntary contraction level. The values shown on the tables represent the average SEMG curve amplitude (µV RMS). For a more complete set of data, the reader is directed to specialty texts. 3,5

Figure 1. Head ROM Segmental Activity

I. Frowning II. Smiling III. Deglutition IV. TMJ Open V. TMJ Closed VI. TMJ Protrusion

Physiology

The muscles of the human head can be generally divided into three distinct groups: those innervated by the facial nerve, those innervated by the trigeminal nerve, and those muscles spanning the occiput and the neck, which are innervated by cervical nerves.4 The muscles innervated by the facial nerve comprise the majority of the head muscles. The embryologic origin is that of the second branchial arch. The expression “Ontogeny Recapitulates Philogeny” may use these muscles as a paradigm. The respiratory muscles of the embryologic gills evolved into the muscles of facial expression. Of great interest, the same muscles may participate as accessory muscles of respiration, consciously or unconsciously. The frontalis/corrugator muscles activity show a very direct connection to the respiratory center: if a person frowns, one is unable to breathe unconsciously at the same time!5 Unlike most muscles of the body, few facial muscles connect directly to bone. Most interconnect to each other and to the trigeminally innervated muscles. One muscle in particular—the fronto-occipitalis muscle—has divided into two bellies with a common very long fascial interconnection. This muscle is better known as the frontalis and the occipitalis.

The trigeminal nerve innervates the muscle of the jaw: temporalis, masseter and the pterygoids. With regards to the temporalis, the human skull has undergone evolutionary changes. The vertex muscular insertion in the crista galli is the same but the crista galli has diminished significantly in size. These muscles perform the high energy-consuming tasks of biting, gnawing, cutting the food, and chewing. They do have tendons that connect directly to the skull bones and also provide the fascial support for the insertions of most muscles innervated by the facial nerve.

The other muscles of the head include the muscles of the external ear and those of the lower occiput and upper neck. In functional terms, the muscles of the external ear are under the conscious control of very few people and are only rarely of pathological significance.

Figure 2. Neck ROM Segmental Activity

I. Flexion Standing II. Extension Standing III. Right Rotation Standing IV. Left Rotation Standing V. Right Bend Standing VI. Left Bend Standing

Rehabilitation Implications

Testing performed on over five hundred symptomatic muscles encompassing the ten major joints showed that the amplitude potentials through any given range of motion conducted at the minimal voluntary contraction level were, on the average, 50% higher than those of the corresponding asymptomatic muscles.3 The abnormal amplitude potentials were most commonly associated with abnormal SEMG electric curve patterns, defined as spasm and hypertonus, as well as co-contractions and co-activation.2,3,5,6

The rehabilitation process of dysfunctional head and neck muscles needs to take into consideration a number of factors. These include, but are not limited to the following: the diagnosis, current treatments, age, overall state of muscular conditioning, motivation to improve the overall muscular function and reduce pain, emotional make-up and emotional state, and concurrent psycho-social and familial change of roles related to the muscular dysfunction and concurrent conditions.4,8 Specifically, the facial muscles have a higher than average resting potential and probably related to ongoing stressors affecting the facial response and behavior.

Table 1 presents the SEMG amplitude potentials data derived from 8 head muscles tested through three temporo-mandibular joint segments of motion and through three facial motions. The testing was conducted in accordance with well established protocols. The level of effort was that of minimal voluntary contraction. The persons tested were not symptomatic for TMJ dysfunction, headaches, or any other head-related symptoms or signs. The table has been organized in an ‘effort descending fashion’, i.e. muscles and motions in descending SEMG amplitude potential indicating decreasing effort. Thus, of the muscles tested, orbicularis oris exhibits the highest overall amplitude potentials of activity and frontalis exhibits the least effort through the motions tested.

“Unlike most muscles of the body, few facial muscles connect directly to bone. Most interconnect to each other and to the trigeminally innervated muscles.”

In terms of ranking of the motions, TMJ closing requires the overall highest average of amplitude potentials summated from the muscles tested while TMJ protraction requires the least. Ranking of the muscles and of the motions from ‘high to low’ allows for a simple, organized observation and understanding of the table contents—both for investigative and rehabilitative purposes.

Analysis

The calculation of the amplitude potentials averages per muscle—and for the group of muscles through the same segments of motion—allowed for another statistical consideration, namely, regression analysis. This consideration is necessary for defining the relationships between any two muscles from the same myotatic unit and helps to elucidate, scientifically, the age-honored expressions of ‘agonism-antagonism.’

Table 3 presents the regression analysis data derived from Table1 in terms of the positive (i.e. synergism, agonism) and negative (i.e. antagonism) correlations between any two given muscles tested with SEMG through the facial expressions and the TMJ segments of motion. A summary of the table shows that the anterior digastric muscle has only negative correlations with all the other muscles in the group. The masseter has almost perfect correlations with all but two of the other muscles. No muscle in the group has only positive correlations with the other members of the same myotatic group. Thus, agonism and antagonism of the muscles of the head could be understood within the realm of the activity amplitude potentials generated through a number of motions. The data from Tables 1 and 3 also document the fact that all muscles of the head function simultaneously at particular levels of activity through any given motion or set of motions. The adage that ‘while the agonist moves, the antagonist is inhibited from motion’ is simply not borne out by observation.

Table 1. Average SEMG amplitude potentials (µV RMS) of the 7 muscles tested with SEMG through the head ROM segments Table 2. Average SEMG amplitude potentials (µV RMS) of the 4 neck muscles tested with SEMG through the neck ROM segments

Tables 2 and 4 document similar sets of data for the neck muscles tested with SEMG through the cervical ROM. Table 2 shows that, of the four muscles tested, the scalenus group shows the highest level of activity amplitude potentials through the segments of the cervical ROM and the upper trapezius muscle shows the least level of activity. The ranking permits the investigator and clinician to organize a given set of data in a logical, hands-on manner.

Table 4 shows that the anterior digastric muscle has only agonistic relationships with the other three muscles in the group. The upper trapezius muscle has antagonistic relationships with the scalenus group and the sternocleidomastoid (SCM), as expected on an anatomical basis.

It is possible to notice again that all the cervical muscles are active at different levels of effort during any motion and there is no ‘inhibition’ of any muscle activity at any time, only engram-related modulation. Each muscle of the head and neck contributed in its own way, at its own level of amplitude potentials, to the concerted movements tested with SEMG dynamic protocols. This is easier visualized pictorially, as shown in Figures 1 and 2.

Discussion

Data presented in Tables 1 through 4 helps provide a better understanding of head and neck pain of muscular origin. One can understand pathology better if one has a good grasp of the underlying physiology. The abnormal can be understood only in terms of comparison with the normal. Asymptomatic muscular activity, as evidenced by SEMG dynamic testing, shows a general pattern of average amplitude potentials—with 95% coefficient intervals—within a 20% range from the average population sample values.11

Muscles associated with pain show markedly different electric potentials pattern during activity and rest.3,5,7 While asymptomatic muscles show minimal resting potentials around 2 microvolts RMS (root mean square), symptomatic muscles show resting potentials far above that value.11

Thus, one general feature of muscles in pain—be it neck pain, tension headache, or TMJ pain, etc.—is that the muscles do not rest at an optimal level. The lack of appropriate rest is obviously associated, on one hand, with poor energy regeneration and, on the other hand, with the accumulation of potentially noxious catabolites— themselves sources of perpetuating pain.5,8,9,12,13,14

Another feature of symptomatic muscle activity amplitude potentials is that of elevated levels of activity.3 The amplitude potentials, as measured by SEMG, represent the summation of the action potentials coursing through the active electrodes per unit of time. If an asymptomatic muscle uses an average number of X action potentials for a given motion and a symptomatic muscle uses on the average 2X action potentials, it stands to reason that the energy supply of the contractile elements of the latter may become easily in deficit and the muscle may fatigue earlier than expected. Often, fatigue is followed by pain, as documented by the fact that resting relieves both the pain and the fatigue. When one considers the two features together—lack of adequate rest and poor energy regeneration, as well as energy over-utilization—one can more easily understand the phenomena of muscular fatigue and pain.4

In the case of the head and neck, the facial muscles are embryologically derived from muscles of respiration and the neck muscles are also accessory muscles of respiration.

All these muscles are easily ‘overcharged’ in sympathetic overflow conditions, as in the case of anxiety and demonstrated elevated resting potentials. The tension can be easily transformed over time to a chronic state of contraction and self-perpetuating pain.

The clinician interested in SEMG investigation and neuromuscular rehabilitation with SEMG may utilize the data from Tables 1 and 3 as a functional database in the clinical work related to tension headaches, TMJ dysfunction, and neck pain. The numerical values shown in the tables are typically higher by over 20% in symptomatic muscles—both in terms of the activity amplitude potentials values and in terms of the resting values as shown in other specialty articles or texts.11 Thus, from the investigative point of view, the clinician may compare the patient values with those of asymptomatic muscles and, from the treatment point of view, one may establish the ‘end-points’ desirable for the rehabilitation program. The same principle applies to the data presented in Tables 2 and 4. These tables show the expected agonist or antagonist relationships of any two given muscles of the head and neck. Symptomatic muscles may show different sets of relationships and different numerical values. The end point of the neuromuscular rehabilitation program, with SEMG or other modalities, should bring about not only the normalization of the symptoms but also the normalization of the amplitude potentials data in terms of the regression analysis shown on those tables.8,15

Table 3. Head and neck muscles correlation coefficients (r) among the 7 muscles tested with SEMG for TMJ ROM Table 4. Neck muscles correlation coefficients (r) among the 4 muscles tested with SEMG

Conclusion

This article presented an SEMG perspective in understanding the muscular contribution of head and neck pain related phenomena. The amplitude potentials of muscular activity of symptomatic muscles were found to be greater than 20% higher (at the 95% confidence level) than those for the average asymptomatic muscles recorded. The values and ranges presented in specialty texts may serve as a ‘template and an end-point’ for the interested clinician, both in the investigative and in the rehabilitative realm, for the treatment of pain in the head region. n

Last updated on: December 22, 2011
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