The History of Muscle Dysfunction and SEMG

The history of muscle pain and dysfunction is viewed through the lens of a four factor theory of histologic (tissue related) issues, psychologic (emotional) issues, sensory motor (movement) issues, and biomechanical (postural) issues. The historical antecedents of both bodywork and surface electromyography are reviewed.

Key words: Surface EMG, SEMG, bodywork, trigger points, posture, emotions, movement

Note: Parts of this article have appeared in The History of SEMG, Jour App Psychophys and Biof, In Press.

Jeffrey R. Cram, PhD and Maya Durie, MEd, CMT


Humans have had to deal with sore muscles since the beginning of time. Initially, muscle assessments and treatments were conducted by hand, and during the last century, the use of electronic instruments came into play.

To put muscle function and the clinical use of Surface electromyography (SEMG) into a perspective of history, is seems prudent to utilize a broad nomothetic net, or conceptual framework. In Clinical Applications for Surface Electromyography, Kasman, Cram and Wolf (1998) consider chronic muscle dysfunction from a four fold perspective: Histologic (Tissue related issues); Psychologic (Psychophysiology and Emotions), Sensorimotor (Movement) and Mechanical Dysfunction (Cumulative Trauma, Posture etc). In this article we will provide a brief historical overview related to each of these four areas. This will provide a deep background for the emergence of the clinical use of SEMG, including information on the history of body work, psychophysiology, rehabilitation and the emergence of electricity and SEMG instrumentation.

Tissue Related Issues

We will begin with issues pertaining to the tissues of the body. The muscle, as an organ system, contains many sensory mechanisms. The muscle spindles tell the nervous system about the instantaneous length and force of contraction of segments of muscle tissue. The golgi tendon organ measures the actual force which the muscle is exerting, and the rufini nucleus of the joints informs the nervous system of the relationship of angles of the bones. However, it is the free nerve ending within the muscle that senses local pain. And it is metabolic disturbances such as too much (lactic) acid or too much internal pressure due to swelling, congestion or edema, which activate the free nerve ending.

From a clinical point of view, up until the last two centuries, palpation and observations about movement and posture were the only tools available for assessing muscle oriented pain. Through the manual sense of touch, the practitioner can learn to feel many things. Is the muscle tissue hard to the touch? Does it feel stiff? Does it have lumps, tough fibers, etc. or is it soft, supple and relaxed? What does the fascia feel like? Is there a normal cranial-sacral rhythm? As you move the body passively through its range of motion, does it seem restricted suggesting a shortened muscle resting length? During active movement, does it appear that the body is using the correct muscles for the movement, or is there a substitution pattern? Is the patient afraid of movement due to pain? Has a trauma become lodged in the nervous system or even the muscle tissue itself? Can one see or feel problems with ligament laxities, or joint fixations? These are just some of the examples of questions we want to address, both by hand and by instrument. . Thus, one could think of body work as a means to help normalize the disturbance of tissue that might foster and create muscle pain, and SEMG as an instrumented way of assessing some of these conditions.

Massage and touch therapy date back many thousands of years. The oldest known book to have been written about massage was from China in 3000 BC. The Egyptians are credited with developing reflexology in 2500 BC. The East Indian holistic health approach called Ayerveda, dates back to around 1800 BC and included massage techniques. The Greeks massaged their athletes prior to the Olympic Games in 776 BC. Even Hypocrites, the father of Western medicine, used a massage technique, friction rub, to treat sprains and dislocations.

The most common massage approach in the Western world is Swedish massage. It had its origins in the early 1800’s and was formulated by Per Heinrik Ling, who developed a repertoire of five basic massage strokes (Claire, 1995). The two main purposes of Swedish massage are to induce the relaxation response in the body that promotes the release of stress and to improve both blood and lymph circulation which helps the body remove toxins more efficiently. Athletes, for example, whose muscles become sore and stiff from physical exercise, overuse or trauma, routinely receive massage. The massage strokes help to relax the muscles allowing more oxygen to flow and assists in flushing lactic acid buildup that comes from exercise. In addition Swedish massage strokes are used to break down adhesions that form around joints from injury thus increasing joint mobility.

Structural Integration or as it is more commonly called, Rolfing, was named after its creator Ida Rolf, and first gained recognition in the 1960’s (Rolf 1989). This method is considered deep tissue bodywork. It works to release the myofascial system, thus re-establishing flexibility and ease of movement in the body. Rolf believed that gravity is the major force that impacts our posture and movement patterns. She postulated that gravity causes the body to slump forward and thus shorten muscles. The Rolf practitioner softens the fascial tissue so it can be realigned properly, allowing the force of gravity to flow through the natural vertical and horizontal planes of the body. The vertical plane is defined as an imaginary plumb line passing through the landmarks of the ear, shoulder joint, hip joint, knee and the ankle. The Rolfer, through a series of 10 bodywork sessions, works to realign all the major body segments to achieve this proper vertical alignment. Rather than working on specific symptoms, the aim of Rolfing is to bring the whole body into alignment thus relieving the cause of the symptoms. By softening the fascia, the body is freed from restrictions and can return to its natural relationship with gravity.

Another bodywork that focuses on the myofascial system is called Myofascial Release (MFR). This work is most commonly associated with John Barnes (1990) a physical therapist who began developing this work in the 1960’s. This approach seeks to release distortions and tension in the fascia thus allowing the body to return to a more healthful balance. In its healthy, natural state fascia, which spreads like a 3 dimensional web throughout the body, is elastic and relaxed. The fascial system’s purpose is to allow the body to absorb compressive forces to the body while protecting the position of the vital organs and retaining the body’s normal shape. Through injury, stress, poor postural habits and illness the fascia develops restrictions. The fascia can become hardened and tight thus pulling muscles and bones out of alignment. This tightening effect can spread over time. The MFR practitioner believes that just removing restrictions in the muscles will not bring lasting results because constrictions in the fascial system will cause the muscle tension to return. The MFR technique uses long, sustained pressure along the fascial planes for at least 3-5 minutes to elongate and stretch the fascia returning it to a gelatinous consistency. As the softening is felt, the practitioner moves the tissue in the direction of ease until the next barrier/restriction to this ease of movement is felt. This softening allows for more freedom of movement and removes the pressure on nerves and restrictions to the blood supply created by the fascial hardening.

The history of muscle pain syndromes has been presented several times (Simons, 1975; Simons, 1976; Port, 1920), and will not be repeated here. Suffice it to say that muscle oriented pain grew out of the clinical concept of rheumatism, and by the mid 1800’s writings were beginning to appear describing “tender points”, localized areas of pain within the muscle. It was not until the early part of the last century that “referred pain” found its way into the medical literature (Kellgren,1938). A little later, a physician by the name of Gutstein ( Kraft, 1968) is credited with introducing the observation of tender spots associated with a “jump sign”. A decade later, Kelly (1945) described “nodules” associated with these tender points along with patterns of referred pain. By this time, the concept of a functional, reflex component to trigger points was beginning to emerge. In 1942, Janet Travell and her colleagues wrote their first paper on trigger points (Travell et al, 1942). By 1976, she had authored or co-authored 38 papers on these tender/trigger points, and summarized her theory that trigger points depended on a feedback mechanism between the trigger point and the central nervous system (Travell, 1976). The prevalence of the problem of trigger points was highlighted by Sola in 1955, finding that 60% of the population had latent, or inactive, trigger points. More recently, Fishbain (1986) noted that 85% of the patients in pain clinics had active trigger points.

Janet Travell, and her colleague David Simons are probably best known for work in this area. Their book, Myofascial Pain and Dysfunction: A Trigger Point Manual (Travell and Simons, 1983) is a very scholarly work which provided the basic foundation of understanding the mechanisms behind trigger points, along with the body maps for knowing where to palpate for trigger points and diagrams of their pain distributions. The trigger point, when palpated feels like a small pea or area of congestion, along with a “taut band” within the muscle. When the taut band is stimulated it twitches, and when the trigger point is pressed upon, it provides several possible responses, including the jump sign and referred pain distribution to distant locations. Trigger points may be treated or cleared by needling them with or without an anesthetic. Or they may be treated with ischemic pressure techniques used in massage therapy. In essence, trigger points within the muscle are a sign of muscle based pain, and are associated with a disturbance in the neuromuscular system and myoelectric potentials within the muscle.

From an electrophysiological perspective, needle EMG studies of trigger points (Weeks and Travell, 1957; Chen, et al, 1998) have shown a high level of spontaneous electrical activity (SEA) at the locations of the trigger points. Hong and Simons (1998), after reviewing the research on this topic, have concluded that myofascial trigger points are related to integrative mechanisms in the spinal cord in response to sensitized nerve fibers associated with SEA and extrafusal endplate noise activity. Another point of view comes from Hubbard and Berkoff (1993) who argue that the SEA emanates from the intrafusal fibers of the muscle spindle. They observed that the SEA was found only in the trigger point zone, and not a few millimeters away in adjacent extrafusal muscle tissue. The location of the SEA is very specific, and has now been termed the “nidus” of the active trigger point. In addition Hubbard (1996) clearly demonstrated that the SEA was diminished or blocked by a beta adrenergic (sympathetic) blocker (phentolamine), and not by an alpha motor blocker (curare). McNulty et al (1994) demonstrated that the SEA activity at the trigger point increased during a stress induction, while the EMG activity in the adjacent extrafusal muscle tissue did not. Earlier research on muscle spindles by Passatore (1985) had clearly demonstrated autonomic innervation of the muscle spindle, and thus provided one of the mechanisms for contraction of the intrafusal muscle fibers.

The question of whether trigger point activity can be seen using SEMG recording techniques has still to be answered. Simon and Dexter (1995) noted that the SEA seen with needle electrodes could not be observed using surface recording techniques. Donaldson, et al (1994), on the other hand, found muscles containing trigger points to be more active when studied using the dynamic SEMG procedure of flexion/extension. Symptomatic muscles showed a higher peak amplitude during movement compared to asymptomatic muscles. Cram and Kasman (1998) have also noted that muscles that contain trigger points tend to have a poor recovery following movement (termed post movement irritability). Lastly, Donaldson (personal communication) has stated that SEMG biofeedback retraining techniques will be impeded if initiated before the trigger point is eradicated from the muscle. Thus, bodywork should precede SEMG retraining when trigger points are present.

The Psychologic and Emotional Level

As Cacioppo et al (1990 ) state, “The skeletomotor system is the final common pathway through which humans interact with and modify their environment.” The implications of this statement have very broad implications for SEMG. The emergence of psychophysiology at the turn of the last century held forth the promise of being able to study complex human behaviors such as thoughts and emotions by monitoring their physiology. Amongst all of the physiological systems available for study, the specificity and sophistication of the neuromuscular or skeletomotor system provided a very strong basis for studying the non-verbal language of emotions.

While Duchenne (1959) is best known for the original studies of the dynamics and functions of intact skeletal muscles, it was Charles Darwin (1872) who announced a rather complex theory of overt emotional behaviors in both animals and humans. Most of his visual observations were limited to emotional displays on the face along with postural gestures. A few years later, William James (1890) introduced an ideomotor theory of emotions, which placed the proprioception of facial muscle activity at the forefront of the emotional experience. Using crude measuring instruments, attempts were made at quantifying the micro-momentary displays of emotions seen on the human face. But it was not until Edmund Jacobson (1925, 1927, 1930, 1931) conducted a series of experiments using biological amplifiers while displaying the signal on the cathode ray tube to monitor the facial muscles of his subjects, that the concept took hold. Using this new technology, clear and convincing evidence was brought forth to show that SEMG responses were evoked by imaginal tasks (visualizations), and that these responses were very minute and highly localized. This was confirmed by R.C. Davis (1939), a major researcher in psychophysiology and SEMG, a few years later.

Facial displays of emotions were given additional life when Ekman, et al. (1969) demonstrated an almost universal quality to the recognition of emotions across cultures. Ekman and Friesen (1975) provided a very powerful guide to understanding facial action patterns in their book Unmasking The Face. During the 1970’s, detailed investigations of SEMG activity of the human face were attempted. Rusalova et al (1975) used method actors and normal subjects to study the intentional display of emotions. When asked to show four emotions (anger, fear, joy and sadness), the method actors showed consistent patterns of facial SEMG for all four emotions, while the untrained subjects were only able to clearly display joy and sadness. Gary Schwartz and his colleagues (Schwartz, et al. 1974, Schwartz, et al 1976) were able to show that facial SEMG allowed one to observe “covert” emotional responses to imaginal tasks of various emotions. Interestingly enough, their study demonstrates one of the primary goals of psychophysiology: To see patterns of emotional responsiveness that could not be seen through usual sensory channels of information (such as seeing the emotions on the face).

Over the years, numerous studies have been done looking at patterns of SEMG in psychiatric populations. For an excellent review of these see Thompson (1988) or Goldstein (1972). As early as 1941, Reusch, et al (1941) had observed that patients who reported feeling fidgety, uncomfortable or tense showed elevations in resting forearm SEMG. Malmo et al (1950) observed the startle response in extremely anxious patients and noted a poor recovery in forearm SEMG, compared to controls. Later Malmo, et al (1951) demonstrated that psychotic and neurotic patients showed higher levels of SEMG in the forearm flexors and neck muscles, compared to controls. Of course, the history of SEMG is replete with contradictory findings. And this could be seen as early as 1956, when Martin (1956) did not replicate Malmo’s findings.

George Whatmore, a student of Edmund Jacobson, studied the arousal patterns of SEMG in various disorders. Whatmore and Ellis (1958) found higher levels of SEMG in the forehead, jaw, forearm and leg muscles in schizophrenics compared to normals. Interestingly enough, the same type of elevated SEMG was noted in severely depressed individuals (Whatmore and Ellis, 1959). These tension levels were observed to decrease as a function of treatment of the depression, and to return prior to relapse.

Whatmore went on to study and treat a variety of disorders using SEMG measurement techniques, culminating in his book The Physiopathology and Treatment of Functional Disorders (Whatmore and Kohli, 1974). Here, he presents a thesis that all psychosomatic disorders are due to dysfunctional muscular efforts that he terms “dysponesis”, or bad energy. He clarifies four types of muscular efforts: Bracing, performing, representation and attention. When one puts too much muscular effort into any one of these four types of efforts, physiological symptoms are thought to develop due to imbalances in the nervous system. According to Whatmore, treatment of these disorders is best conducted by teaching the patient how to reduce these dysponetic efforts. To do this, he embellished Jacobson’s Progressive Relaxation Technique (Jacobson, 1976) in 1952, by adding an analog audio tone (or feedback) driven by the SEMG signal (Whatmore and Kohli, 1974). In some ways, Whatmore should be considered to have created the first SEMG biofeedback instrument, and thus is the unrecognized father of SEMG biofeedback.

Eventually the “key muscle” hypothesis emerged (Alexander and Smith, 1979), in which the Frontalis or forearm musculature was thought to be a strong indicator of overall muscle tension. Unfortunately, several studies have reported low correlations between the frontal or forearm site to other sites (Suarez, et al, 1979; Shedivy and Kleinman, 1977). Interestingly enough, Cahn et al (1990) found the T10 paraspinals to correlate 0.76 with the overall resting muscle activity of 24 sites. Perhaps the mid back is the best indicator of general tension levels. However, the vast majority of the SEMG literature supports a model of specificity of the neuromuscular system rather than a generalized arousal model.

Clinically, several treatment techniques were developed to treat the emotional layer of muscular disturbance. The technique of progressive relaxation was introduced by Edmund Jacobson in 1934 (Jacobson, 1976). Jacobson’s thesis was that nearly all muscular and functional disorders (eg, irritable bowel syndrome) were due to a dysregulation of the nervous system and that all of these could be treated with his technique. In some ways, his therapy was replaced with Valium™ when the pharmaceutical revolution took place in the 1950’s.

Jacobson developed a set of exercises in which the patient was instructed in how to systematically tense and release the major muscle groups of the body. The patient would initially be taught to tense the muscles to the extent that they would vibrate with intense effort, and then “zero down”, and let go of the muscle contraction or tension as completely as possible. As time went on the patient was to learn how to let go of small, even minute levels of tension. This was the key to his success. Below is a list of 16 muscle sets he would focus upon: Forearm (wrist flexors and extensors), upper arm (biceps and triceps), lower leg (foot flexors and extensors), upper leg (quadriceps and hamstrings), abdomen and back extensors, chest and scapular retractors, shoulders and neck, forehead, eyes, lips and jaw. Such tensing and releasing are commonly found in SEMG biofeedback work.

Autogenics training, a more cognitive approach, was developed in Germany in the 1950’s by Wolfgang Luthe (Luthe, 1969). His intense interest in the phenomena of hypnosis and the effects it could have on the human body led he and his colleagues to begin researching the effects of words on physical functioning. Using physiological monitoring devices they tested over a thousand phrases. From this, a series of key phrases or “formulae” were discovered to consistently evoke physiological responses. The key word for the neuromuscular system was “heavy”, and the phrase consisted of four variations of “my right arm is heavy” for the different limbs. The autogenic (self-cleansing) phrases are as follows and may be used to induce emotional and general physiological relaxation: “I am completely calm.” “My right arm is heavy.” “My right arm is warm.” “My heart beat is slow and regular.” “My breathing is slow and regular.” “My abdomen flows warmly.” “My forehead is cool.”

A number of bodywork therapies have been created to work with the emotions. The Rosen method of bodywork was created in the mid 1900’s by Marion Rosen (Mayland, 1984), a physical therapist. She believes that old, forgotten emotions and memories are stored in the body and that these are the source of the holding patterns that cause pain and dysfunction. The Rosen method consists of gentle touch. With the fingertips, pressure is applied to areas of tension in the muscles. The pressure is applied slowly and seeks to meet the level at which the resistance, or muscle tension is felt. The practitioner uses one hand to work with the muscle tension while the other hand remains still to listen for changes in the tissue or in the movement of the breath. These changes typically indicate some emotional release has occurred.

Rosen believes that as we become socialized we develop patterns of holding and restriction in order to be socially appropriate. We tighten our muscles to inhibit the expression of emotions and physical motions of defense, such as hitting, kicking or pushing away. These inhibited emotions and motions are stored in the body limiting our freedom of expression and movement. Restriction of breathing is a key way in which we learn to inhibit our emotions. Thus freeing up the tightness in the diaphragm is a major focus in the Rosen work. As muscle tension and holding patterns from past injury and trauma are released the individual is freer to respond more authentically to the present moment.

Sensory Motor Aspects: Movement Oriented Approaches and Rehabilitation.

As surface EMG emerged in the 1940’s, studies on dynamic movement began. Inman and his colleagues (1944), for example, conducted a widely accepted SEMG study that was able to measure muscle activity associated with movements of the shoulder. This interest in dynamic movement quickly spread to the clinical arena and by the early 1950s, Floyd and Silver (1955), presented an exceptionally strong study of SEMG and the erector spinae muscles. They clearly demonstrated that as the person goes through forward flexion of the trunk the back muscles shut off as the trunk goes out onto ligament support. Thirty years later, Wolf et. al. (1978, 1982) utilized SEMG biofeedback techniques in the assessment and treatment of low back pain. For a comprehensive review of the history of SEMG assessment and biofeedback treatments for low back pain up into the early 1990’s see a chapter by Sherman and Arena (1994) or an earlier review article by Dolce and Raczynski (1985).

During the 1960’s, biofeedback was born. Part of the impetus for this birth was the work on single motor unit training of the neuromuscular system by Basmajian (1963). While this type of training entailed the use of fine wire electrodes rather than surface electrodes, it clearly demonstrated that the neuromuscular system could be trained using EMG biofeedback techniques, down to its most basic element: The single motor unit. With all the excitement around his discovery, Basmajian conceived of an international forum to share information on SEMG, and in 1965, the International Society of Electrophysiological Kinesiology (ISEK) was formed. It still exists today and provides one of the only journals that specifically addresses issues pertaining to SEMG: The Journal of Electromyography and Kinesiology.

Nearly 30 years later, Cram (1990) edited a book on the Clinical EMG for Surface Recordings, Volume 2 and formed an organization which focused on the clinically applied aspects of surface EMG. The Surface EMG Society of North America (SESNA) still exists and is currently found as a chapter of the Association for Applied Psychophysiology and Biofeedback (AAPB).

From a biofeedback perspective, the history of surface EMG began with Elmer Green (1969) at the Menninger Clinic, where he modified the concepts behind Basmajian’s single motor unit training paradigm and applied these to a general relaxation training paradigm. A few years later, Budzynski and Stoyva (1970) began using SEMG feedback to treat muscle contraction headaches. From there, the SEMG biofeedback arena began to rapidly expand.

Clinical use of SEMG biofeedback for the treatment of more specific neuromuscular disorders also began in the 1960’s. Hardyck et al (1966) were amongst the first to use SEMG to teach students not to sub-vocalize during silent reading, and thus accelerate their reading development. Booker et al. (1969) demonstrated neuromuscular re-education methods for patients with various conditions, and Johnson and Garton (1973) utilized SEMG to assist in the restoration of function of hemiplegic patients. Brucker began working with stroke and spinal cord injured patients in the 1980’s, taking on cases where traditional physical therapies had given up. His work on neuromuscular re-education has recently been published (Brucker, 1996), reporting success where others had failed. In addition, there is a meta-analysis (Moreland, et al, 1998) comparing traditional methods of treating cardiovascular stroke to traditional methods augmented with the use of SEMG biofeedback. Across studies, they found that the use of SEMG biofeedback improved the outcome of the therapy. Given these findings, we are continually amazed that SEMG biofeedback isn’t part of the standards of care for the stroke patient.

Neuromuscular applications in dentistry were introduced in the early 1970’s by Bernard Jankelson (1969). Jankelson recognized that the traditional concept of “centric relation” failed to consider the status of mandibular posturing muscles. He developed procedures that used SEMG as an aid in determining a physiologically balanced occlusion and building of orthotics (“splints”) for treatment of myofacial pain disorders. In addition, Cooper (1991) and Yamashita (1985), have extensively studied the role of SEMG in the assessment, understanding and treatment of occlusal and temporomandibular joint (TMJ) disorders. Recently R. Jankelson (1998) has summarized this type of clinical work. Lastly, Glaros (1996) and Hudzynski (1990) have extensively studied the role of SEMG in the psychophysiological assessment, understanding and treatment of Temporal Manibuluar Joint (TMJ) disorders.

During the late 1980’s, Donaldson (1990) normalized his SEMG recordings by calculating the degree of symmetry of homologous muscle pairs during dynamic movement. He studied the degree of symmetrical recruitment during symmetrical and asymmetrical movement patterns in both normals and pain patients, concluding that a 20% asymmetry provided adequate sensitivity between the two groups. In addition, Donaldson popularized the concept of “co-contractions”. During asymmetrical movements asymmetrical recruitment patterns should be seen in homologous muscle pairs. Again, when this doesn’t occur an abnormal finding is identified which potentially could be treated using SEMG biofeedback retraining techniques. More recently, Sella (1995) expanded Donaldson’s concepts of monitoring homologous muscle pairs to a higher level, presenting a systematic method of testing many of the muscles of the human body for deficiencies.

Also during the 1980’s, Will Taylor (1990) introduced the concept of measuring synergy patterns in the upper and lower trapezius during abduction of the arm. Following the work of Karol Lewit (1991), Taylor noted that myalgias in the upper quarter were commonly associated with a “postural” muscle doing the work of their “phasic” counterparts. For example, in upper back or neck pain, the upper trapezius (a phasic muscle) commonly dominates the stabilizing muscular action associated with abduction of the arm to 90 degrees, even though it should share this work load with the lower trapezius (a postural muscle). The hyperactivity of the upper trapezius, then, is seen as being facilitated by the inhibition of the lower traps. Susan Middaugh (1994) has also clearly delineated the role of a hyperactive upper trapezius in headache, neck and shoulder pain. She came to the conclusion that almost all of the dysfunctional patterns in the upper back involve hyperactivity of upper trapezius.

The American, European and international academic communities have provided a strong fundamental basis for understanding electromyography in general and surface electromyography in particular. Space limits the ability to acknowledge the many contributors to this field, and thus I can provide only a limited sample of the major contributors. The influence of DeLuca and his colleagues at the Neuromuscular Research Institute in Boston cannot be overlooked. Much of their work on spectral analysis and muscle fatigue (DeLuca, 1984) has shed light on both the physiology of muscle and its methods of measurement. Kadefors (1978) from Sweden, and Masuda (1999) and Sudyoma (1981) from Japan have also contributed to our understanding of muscle fatigue. Clinically, the role of muscle fatigue in back pain was clearly delineated in a study by Roy et al (1989).

The work of the Scandinavian community on tension myalgia in the workplace is very impressive. Hagg (1991) has provided a vast amount of information concerning work and the upper trapezius muscle, as have Maithessen (1995), Hagberg (1981), Westgaard (1987) and Jonsson (1978). They have clearly added to our understanding of muscle dysfunctions in the workplace. Veiersted (1993) and Hagg et al (1997) should also be recognized for their studies on the importance of rest. In addition, an excellent summary of SEMG issues related to the workplace may also be found in an edition by Soderberg (1992).

The Europeans have also focused strongly on the engineering and technical aspects of SEMG, and have created an organization called Surface EMG for Non-Invasive Study of Muscles (SENIAM). Through this effort, several books have been created which look at standardizing the recording methods for SEMG (Hermens, et al 1999), the state of the art for SEMG sensors and sensor placements (Hermens and Freiks, 1997), European activities on SEMG (Hermens et al, 1996), and European applications on SEMG (Hermens, 1997). They have also created a “concerted action” (Merletti and Hermens, 2000) to help clarify technical standards for SEMG.

Clinically, there have been several body work techniques developed to work dynamically with muscle oriented pain. The Feldenkrais method (1972) is an approach to movement re-education. Moshe Feldenkrais believed that we learned the vast majority of our movement patterns during the first few years of life, and then repeat these compulsively to the exclusion of other possible movement patterns. He is so bold as to say that we use only five percent of our total potential movement ability.

He also believes in the innate movement wisdom of the body. The goal of the Feldenkrais practitioner is to assist the patient in experiencing more efficient forms of movement. Once experienced, the ease associated with this new pattern may automatically become part of the patient’s movement repertoire, or may consciously become available to the patient.

Feldenkrais was a master at understanding and breaking down movement patterns into their components. As part of a Feldenkrais session, the therapist might ask the patient to begin with their habitual pattern. The therapist might then scramble these components, introducing chaos into the system, in order to disrupt the habitual patterns. For example, normally the eyes move in the same direction as the rotation of the head. In working with neck problems, the Feldenkrais practitioner might ask the patient to move the eyes in the opposite direction of the head. In general, there are six elements to doing Feldenkrais movements. They are: Be consciously aware of each movement, move in a relaxed fashion, make the movements very small, make them slowly, and never go into pain. Lastly, also practice these movements through visualization only. For some nice examples of Feldenkrais exercises please consult Relaxercize by David Zemach-Bersin et al (1990).

The Trager Approach was developed by Milton Trager in the mid 1900’s (Juhan, 1989; Claire, 1995). The underlying theory of this work is that pain and dysfunction begin and are maintained in the unconscious portion of the mind. His approach seeks to communicate with the unconscious aspect of the client’s mind and to re-educate the nervous system toward a more relaxed way of being. To do this, the Trager practitioner enters into a deep meditative state which Trager called a “hookup”. While in this active, yet meditative state, the practitioner moves the client’s body while mentally asking the client’s unconscious such questions as , “How should this feel? What could be softer? Lighter? Freer?” The practitioner is at the same time being aware of their own body seeking to be as light, free and soft as s/he can be as well. In this way her/his body can transmit this way of being to the client’s body.

The technique consists of gentle wiggling and jiggling of different parts of the body. Through this jiggling, habitual holding patterns in the nervous system are disturbed, introducing chaos into the muscular system thus allowing for a healthier reorganization of the energy patterns. During a Trager session the practitioner encourages the client to become aware of changes in their body and to remember how this new sense of ease or lightness feels. This is called “recall” and is felt to assist in the mind’s ability to release these habitual holding patterns.

Biomechanics and The Role Of Posture.

Posture is the foundation upon which movement rides. Therefore, the history of SEMG would not be complete without some information concerning posture. Posture can be thought of as a purely biomechanical event, bearing weight against gravity, or it may be thought of as a manifestation of emotions. We will briefly look at both.

Janet Price and her colleagues (1948) in the 1940’s, began to study clinical populations of back pain patients using SEMG. They noted that SEMG activation patterns began to migrate away from the site of original injury to other muscle sets. This study represents the first documentation on antalgic postures or protective guarding patterns.

There is an SEMG assessment technique that provides a “big picture” of bracing and holding patterns, thus allowing the practitioner to describe and quantify postural disturbances from a muscular point of view. The muscle scanning procedure developed by Cram (1986) utilizes “hand held” electrodes which allow one to quickly sample the right and left aspect of multiple muscle groups. If one were to sample the paraspinal muscles at each 4th vertebral segment, for example, the postural pattern of resting tone along the spine would emerge. Using this technique, Cram and Engstrom (1986) studied 104 normal individuals and compared them to over 200 chronic pain patients to demonstrate the clinical sensitivity of this technique in studying pain related disorders. From this study a normative database was developed which may be used to guide clinical interpretations of patterns or sites of muscular activation, asymmetrical activation patterns, and postural (antalgic) disturbances. Cram and Kasman (1998) present a clear case study of “antalgic” or painful posture. Here activations on the left erector spinae are evident as the patient’s weight shifts away from a right sciatic type pain. With the ability to see SEMG resting tone at higher vertebral sites, this case study allows one to see a compensatory bracing pattern in the right T2 and C4 paraspinals. It is no wonder that patients with low back pain, as Price had noted, eventually begin to hurt in the upper back and neck as well.

The role of SEMG in the chiropractic community cannot be ignored, since it has adopted paraspinal muscle scanning as a method for helping to describe the neuromuscular elements of the subluxation complex (Brody, 1987; Kent and Hyde, 1987). A few studies have demonstrated the usefulness of SEMG paraspinal scanning as an outcome measure (Myerowitz,1994). Cram (1993) has encouraged the chiropractic community to expand the scope of their use of SEMG to include dynamic procedures as well.

Florence Kendall (1993), in her most recent book Muscles: Testing and Function, provides a beautiful guide to understanding and assessing the mechanical aspects of posture. It shows stances against postural grids, and simultaneously describes postural disturbances for the involved muscles. Along with the “ideal posture”, the faulty postures of Kyphosis-lordosis; Sway Back; Military Type; Flat Back and Scoliosis are presented. Special sections on head position, shoulders and scapulae and knees, feet and legs are available.

Body oriented psychotherapists and Somatics practitioners have also focused upon the role of emotions and posture in neuromuscular health. Stanley Keleman (1985) has developed a model of layers and compartments in understanding how the body and muscles function as a whole in physical and emotional health. He conceptualizes the body as having three compartments or pouches located roughly in the abdomen, chest and head. In addition he views the body as having three distinct layers. The outer layer represents our interaction with the world and includes the nervous system and the skin. The middle layer encompasses the muscles, bones and connective tissues. The inner layer consists of the internal organs of digestion, assimilation, respiration and distribution. The biological and psychological integrity of the body entails adequate pumping of life bearing fluids and energy through all three layers and between the all three compartments.

According to Keleman, the fluidity of these compartments may become disturbed by stress and insults to the organism. He describes a startle/stress continuum which affects posture through six variations. The first three postures involve getting bigger and expanding outward. The postures evolve from a rigid cautionary stance to a threatened bracing and finally a turning, as if getting ready to run away. The next three postures involve getting smaller, shorter and becoming fixed. These represent a freezing type response. The postures evolve through the stages of a contracted bracing, to a withdrawal and submission and finally a downward collapse in defeat. Over time, if the stressors are perpetuated, Keleman suggests that there will be changes in the density of the layers and the directions in which he pouches pulsate or flow. The postural muscles and postures involved can lead to one of four somatic defenses: Rigid and controlled; Dense and shamed; Swollen and manipulative; and Collapsed compliant. Each type has a variety of complex physical, social and psychological sequeli.

Thomas Hanna (1988), who studied with Feldenkrais, has described two common reflexive postural stances. The first is called the “Red Light” reflex and is best represented as a withdrawal response from perceived stress or danger. Here, the facial muscles contract, the shoulders rise, the head moves forward, the elbows and knees bend and the abdominal muscles contract, pulling the trunk forward and the chest down. This limits the ability to breathe and affects the heart and other internal organs. This may become habitual in individuals who live in a high state of alertness or fear.

The second is the “Green Light” reflex. It is considered assertive and active. This reflexive pattern opens the eyes, pulls the neck backwards, the shoulders downward, hyper extends the elbows and knees, lifts the chest and activates the lumbar muscles to hyperextend the back. When repeatedly triggered, as it commonly is in Western society, Hanna suggests that it may be the primary culprit for the high incidence of back pain.

Both reflexes are triggered by one’s response to their environment. While the red light reflex brings us to a stop, the green light puts us into action. Both reflexes co-exist. There is a competition between these two. Over time, both postural reflexes may be seen in the same individual. This Hanna refers to as the “senile reflex”. One reflex may dominate over the other. If, for example, the red light reflex has been dominant over the course of a person’s life, they will have a more pronounced stooped over posture and may even develop a dowager hump.

Hanna (1988) has presented a very nice series of sensorimotor exercises in his book Somatics. These floor exercises focus on becoming sensorially aware of movement, and may be used to break up dysfunctional habitual postural reflexes and patterns. Underlying the emphasis on sensory awareness is Hanna’s concept of “sensory motor amnesia”. He utilizes these floor exercises to bring a renewed sensory awareness to the afflicted areas. The set of floor exercises include learning to control the extensor muscles of the back, the flexor muscles of the stomach, the muscles of the waist, efforts related to rotation of the trunk, controlling of the hip joints and legs, and controlling of the muscles of the neck and shoulders. There are also exercises for improving breathing and improving walking. Practitioners using SEMG to treat various pain disorders may want to familiarize themselves with Hanna’s work.

Another approach to understanding and treating posture was developed by F. Matthias Alexander (Alexander, 1985; Maisel, 1990) at the turn of the last century. This is a system of postural re-education with a focus on the proper relationship of the head, neck and torso. Alexander posited that most people have learned a less than optimal way of carrying themselves, thus causing pain and discomfort. He states that when the head and neck are in proper alignment with the torso, the head “floats” upward and the neck and spine are released and lengthened. The Alexander teacher provides a combination of gentle guidance by touch and verbal instruction to register an awareness of the student’s postural alignment. There are three steps to the Alexander process that the SEMG practitioner might want to adopt in their own work. The first is to assist a student in becoming consciously aware of their posture and movement patterns. The second is to master the ability to inhibit dysfunctional and habitual patterns. The third step is to consciously break old habits and establish new and better postural and movement patterns. The SEMG practitioner working on cervical problems would be wise to familiarize themselves with the tactile and verbal suggestions utilized in this technique.

Electrode Atlases

In the world of SEMG, knowing where to place the recording electrodes is essential. The SEMG electrodes are like little microphones which “listen” for the muscle action potentials or MAPS. Having these microphones in the right locations facilitates the nature of the recording. The SENIAM group has demonstrated that slight changes in the placement of the recording electrodes may dramatically alter the amplitude and quality of the SEMG recording (Hermens, 1999).

The first SEMG electrode atlas was constructed by Davis (1952). Since much of the original SEMG research was conducted by Davis, he provided researchers with electrode placement maps to assist in the standardization of SEMG recordings. Nearly 30 years later, Basmajian and Blumenstein (1989) wrote a small book to guide electrode placements. This expanded and updated the initial recommendations of Davis to include more sites relevant to rehabilitation. Cram and Kasman (1998) produced an electrode atlas of 69 sites, classifying each recording site for the quality of the recording (specific, quasi-specific and general recordings). Since SEMG recordings may be subject to issues of volume conduction from surrounding and distant muscles, “specific” recordings were felt to be relatively free of such contamination. “Quasi-specific” sites were thought to record from the muscle named, as well as volume conducted signals from surrounding muscles. “General” recordings were considered recordings from a region rather than from specific muscles. In addition to the sites for placement, sample recording from standardized movements are presented in both raw SEMG and processed modes.

SENIAM, the European effort, has also created a very concise and well illustrated book on standardized SEMG electrode placements for 27 muscle sites across the areas of the shoulder and neck, the back muscles, the arm and hand, the upper leg and hip, and the lower leg (Hermens, et al, 1999).

A Brief History Of Electricity and SEMG Instrumentation

The history of SEMG has to do with the discovery of electricity, and the ability to see phenomona through the aid of instruments which one could not see, feel or touch with the normal senses.

The theme of the development of SEMG can be traced back to Francesco Redi (1617) in the mid 1600’s, whose work with the electric ray fish documented that a highly specialized muscle was the source of its energy. By 1773, Walsh had been able to clearly demonstrate that the eel’s muscle tissue could generate a spark of electricity. During the 1790’s, Luigi and Lucial Galvani (1953) had conducted a series of studies that demonstrated that muscle contractions could be evoked by the discharge of static electricity. Concurrently, Volta (1792) had developed a powerful tool that could be used to generate electricity, which, incidentally, could be used to stimulate muscle. The technique of using electricity to stimulate muscles gained wide attention during the 1800’s. The documentation of the use of electrical stimulation to study muscle function was conducted by Duchenne (1959). As mentioned earlier, his work is truly the first systematic study of the dynamics and function of the intact muscle.

It was not until the early 1800’s, that the galvanometer, a robust tool for measuring electrical currents and therefore muscle activity was invented. In 1838, Matteucci (1844) used the galvanometer to clearly demonstrate an electrical potential between an excised frog’s nerve and its damaged muscle. By 1849, Du Bois-Reymond (1983) had provided the first evidence of electrical activity in human muscles during voluntary contraction. Du Bois-Reymond’s classic experiment involved placing blotting cloth on each of the hands or forearms of his subject and immersing them in separate vats of saline solution, while connecting the electrodes to the galvanonmeter. He noted very minute but very consistent and predictable deflections whenever the subject flexed his hand or arm. He thought that the magnitude was diminished by the impedance of the skin, and therefore removed a portion of the skin of the subject, replaced the electrodes and noted a dramatic increase in the magnitude of the signal during wrist flexion. Please note that the importance of good skin preparation before electrode placement has been present from the very beginning of SEMG. By the early 1900’s, Pratt (1917) had begun to demonstrate that the magnitude of the energy associated with muscle contraction was due to muscle and the recruitment of individual muscle fibers, rather than due to the size of the neural impulse. And by 1922, Gasser and Eralanger (1921) were able to use the newly invented cathode ray oscilloscope to show the signals from muscles. This feat won them the Nobel prize in 1944.

The concentric needle electrode, developed by Adrian and Bronk (1929) in 1929 provided a powerful tool , still widely used today for needle EMG studies. Vacuum tube amplifiers (Mathews, 1934) and later solid state differential amplifiers made it possible to obtain a better and cleaner EMG signal. By 1962, John Basmajian (1962) had compiled all of the information available on electromyography into his book Muscles Alive. Over the years, it has been updated through five editions. With the last edition, he shared the book with DeLuca (Basmajian and Deluca, 1983).

DeLuca pioneered much of the mathematical language and models for understanding motor unit action potential (MUAP) of the EMG (DeLuca, 1979). This modeling was further elaborated upon by Dimitorova (1974), who provided mathematical tools for understanding the biophysics of EMG, and therefore the information contained within the signal. Later Lindstrom (1977) provided the mathematical foundation for decomposing the EMG using spectral analysis. Spectral analysis was further considered in Deluca’s (1984) description of muscle fatigue. Broman et al (1985) have induced a method of linear electrode arrays and double differential amplification techniques which allows the researcher to see the electrophysiological characteristics of the MUAP as it travels down the muscle fiber. Recently Merletti (2002) has presented information on the use of these linear electrode arrays.


Surface EMG technology is found across many disciplines, ranging from manual therapies to psychology. Those providers who have come into SEMG work through psychology may have been unfamiliar with some of the bodywork approaches to treatment, and the manual therapists may have been unfamiliar with the emotional aspects of SEMG.

Hopefully, by reviewing the history of the four domains of tissue, emotions, movement and posture, a broad understanding of SEMG can be appreciated by all disciplines involved. It is hoped that such a broad exposure will encourage providers to learn more about applications that they are unfamiliar with, to consider referral to other providers when necessary, or to learn how to blend new techniques into what they are doing. As one uses SEMG to its fullest potential, one learns to walk the mind-body interface, and to practice a body oriented psychotherapy.

With that in mind, as practitioners, we all must attempt to use SEMG responsibly. As far back as 1977, DeLuca (1977) was warning about the uses and abuses of SEMG. By the 1990’s, several negative reviews on surface EMG began to appear in the scientific literature (Haig, 1996; Rechtien, 1999; Pullman, 2000). In response to the initial critique on SEMG, the European Community sponsored a “concerted action” on Surface EMG for Non-Invasive Assessment of Muscles (SENIAM), founded in 1996 and funded for three years (Merletti, et al, 2000). This has resulted in a concise set of recommendations for the use of SEMG (Hermens, et al, 1999). We would all be well advised to join the Europeans in embracing their technical standards for the use of SEMG. In addition, we would be wise to study the clinical protocols for the use of SEMG presented by Kasman et al (1998).


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