A Muscular Approach to Headache
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
I. Frowning II. Smiling III. Deglutition IV. TMJ Open V. TMJ Closed VI. TMJ Protrusion
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.
I. Flexion Standing II. Extension Standing III. Right Rotation Standing IV. Left Rotation Standing V. Right Bend Standing VI. Left Bend Standing
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.