Because the electrodes are the listening devices for picking up SEMG activity, knowing where to place the that it is a little rough. Some electrode preparation pads
actually contain a small amount of pumice to facilitate abrasion. Avoid cotton balls and tissues for this purpose:
They simply do not do the intended job of removing the oils and top layer of dead or hornified skin so that the bi- ological potentials can easily reach the recording elec- trodes. When the task is done well, a slight rubor is commonly seen.
Site preparation sometimes includes the application of a small amount of electrode paste or gel directly onto the recording site: Take a cotton swab, dip it into the electrode paste, apply it to the skin, and then spin it lightly at the location where the electrode will be placed. Whether the practitioner preapplies electrode paste to the skin, applies it directly to the electrode, or uses pregelled electrodes, the electrolytic medium pene- trates the sweat glands and provides a link to the poten- tials residing below the skin. This greatly facilitates the transfer of the motor unit action potentials.
In situations where the instrument manufacturer pro- vides dry electrodes for the active electrodes, these elec- trodes eventually become moistened by perspiration of the skin. When the dry electrodes are applied to the skin, the skin eventually opens up its pores and exudes sweat in the body’s natural attempt to shed the foreign object. Thus, the body supplies its own electrolytic
25 2423 2221 2019 1817 1615 1413 1211 109 87 65 43 21
0 5
Time (sec) Scan window
Micromhos Kilohms
10 15 20 25 30 35 40 45 50 55 60
1000 200 No paste/no abrade No paste/abrade Paste/no abrade Paste/abrade
100 66 50 40
Figure 4–4 Impedance as a function of the type of electrode site preparation.
Source:Reprinted with permission from J. R. Cram and D. Rommen, Skin Preparation and Validity of EMG Scanning Procedure, Biofeedback and Self Regulation, Vol. 14, No. 4, pp. 75–82, ©1989, Plenum Publishing.
electrodes is a very important part of the process.
Although only a small amount of information is avail- able on this topic, Fridlund and Cacioppo4have high- lighted six elements that can improve the fidelity of SEMG recordings:
1. Select the appropriate proximity of a proposed site to the underlying muscle mass, keeping the minimum amount of tissue between the electrodes and the muscle fibers themselves.
2. Select the appropriate position of the electrodes relative to the muscle fibers. Whenever possible, the electrodes should be placed parallel to the fibers to maximize sensitivity and selectivity (see Figure 4–5). Perpendicular placements tend to lead to greater common mode rejection and less selectivity.
3. Avoid straddling the motor end plate region. If this is done, the amplitudes observed are typically lower owing to differential
amplification. Placing electrodes a little off the center of the muscle is better positioning.
4. Choose sites that are easy to locate (sites that have good anatomical landmarks to facilitate reliable placement of electrodes during subsequent recording sessions).
5. Choose sites that do not unduly obstruct vision or movement. Avoid areas that present problems owing to skin folds, bony obstruction, and other factors.
6. Minimize cross-talk from proximal deep or superficial muscles by selecting the best electrode size and interelectrode spacing.
The practitioner must also decide which muscles are of clinical interest. One strategy for making this decision is the educated guess. Here the practitioner considers which muscle or muscles might be associated with the clinical phenomenon being studied or treated. The prac- titioner then places the electrodes over those muscle sites to test his or her clinical assumptions. This is a good model, because it encourages the practitioner to learn about muscle synergy patterns and to begin to see the movement and postural and emotional patterns as part of a larger whole.
A common but naive strategy is to place electrodes only over the area that hurts or is dysfunctional. For ex- ample, the practitioner might study only the upper trapezius muscle in someone with neck or shoulder pain. Although this may be a reasonable place to start, such a narrow focus on SEMG recordings for solitary muscles places artificial limits on the information that is obtained. The shortcoming of this strategy becomes clear when one considers the possibility that pain may be referred from a more distal site.
An alternative strategy is to use validated clinical pro- tocols for SEMG recordings for specific disorders. For the patient with upper quarter pain, protocols have been developed that explore asymmetries and syner- gies of not only the upper trapezius but also the lower trapezius, and perhaps the serratus anterior.5Such pro- tocols are designed to provide the practitioner with a limited, but very practical, approach to understanding the roles that muscles play in a given dysfunction.
Protocols often work well, but when they fail, the practi- tioner must give further thought.
An extension of the protocol strategy is to develop variations based on clinical reasoning, knowledge of anatomy, and pathokinesiology. For the patient with shoulder pain, for example, the practitioner may want to consider also monitoring the deltoids, the infra- spinatus, or the pectoralis. Finally, the practitioner should be open to the possibility that the disorder may be due to postural or emotional components or have its source in fascia, bone, or blood vessel. Given the complexity of the problem, the practitioner should have a strategy of going from one level of assessment to another, until all of the possible contributing factors have been examined.
In considering the strategy for assessing the postural component of dysfunction, it helpful to incorporate the sampling technique called muscle scanning.6Instead of studying just one or two sites while the patient is sitting and standing, muscle scanning allows the right and left
1 3
Parallel
Perpendicular 4
2
Figure 4–5 Relationship of muscle fibers to electrode placement.
Source:Copyright ©J. R. Cram, Clinical EMG for Surface Recordings: Volume 2, Clinical Resources, Inc.
upper back. Wrist-to-wrist electrode placements allow the practitioner to see clearly any holding patterns or ac- tivations in the upper extremities, upper back, and chest. The ankle-to-ankle leads do the same for the lower extremities, buttocks, low back, and abdomen.
In dynamic relaxation protocols, such as the ones de- veloped by Ettare,8the right and left aspects of general regions are considered. For example, the right and left trapezius placement strategy would allow the practi- tioner to monitor the right and left aspects for the region of the upper back. Treatment would be directed at teaching the patient how to quiet the muscles quickly following their activation.
Strategies of electrode placement associated with specific muscle monitoring typically involve closely spaced electrodes that are placed parallel to muscle fibers or in areas with the least cross-talk. The elec- trodes are most commonly placed directly over or slightly lateral to the belly of the muscle. The electrode placement strategy for specifically monitoring the upper fibers of the trapezius, for example, is to place the recording electrode on the ridge of the shoulder, slightly lateral to the center of the muscle belly, and with the electrodes running in the direction of the fibers. In con- sidering placement of electrodes for muscles that are partially covered by another muscle or a muscle that has very close proximity to neighboring muscles, it is sometimes possible to place recording electrodes on a distal portion of the muscle to avoid or minimize cross- talk. Recordings from the flexor digitorum in the fore- arm are a good example of this strategy. Although this placement is not directly over the belly of the flexor dig- itorum muscle, it does detect enough of the action po- tentials from the distal portion of its muscle fibers to reflect finger (as opposed to wrist) movement. Specific placements of electrodes may be used to assess pat- terns of muscle recruitment associated with movement.
They are commonly used to treat the patient by teaching the patient to activate (“uptrain”) a specific muscle to improve the muscular effort. They may also be used to
“downtrain” a specific muscle—to teach the patient specifically to turn off the recruitment of a muscle fol- lowing its use.
Chapters 5 and 6 explore in great detail the place- ment of electrodes for both static and dynamic procedures. These chapters contain specific recom- mendations about placement sites, along with exam- ples of what one would expect to see given a particular electrode placement.
aspects of multiple muscle groups to be studied in both the sitting and standing positions quickly using a hand- held scanner. The handheld scanner provides a chassis for two (or three) direct contact electrodes. These recording electrodes are held in place over a muscle by hand with a light pressure. For more information, see Chapter 6. The values that are obtained are then either compared to a normative reference group or are nor- malized and compared within the individual to deter- mine which muscles are relatively hyperactive versus hypoactive. Right and left asymmetries may be consid- ered within the context of various vertebral segments.
Weight shifting or antalgic postures are commonly ob- served. Imbalances in the upper back can better be un- derstood when imbalances in the lower back are also included. Once these relationships have been deter- mined, the clinician can attach electrodes to gain a bet- ter understanding of how these relationships affect movement.
Strategies for studying or identifying the emotional aspect of the neuromuscular system should be consid- ered as well. It is common for practitioners to place widely spaced electrodes on the frontal muscle, expose the patient to stressful events, and record the patient’s re- actions. Although such a recording procedure allows the practitioner to measure some of the major negative emotional states seen on the human face (e.g., anger, fear, and sadness), it does not provide information con- cerning specific emotional activation at the injured site or its homologous counterpart. One may broaden the search for an emotional component by placing a set of electrodes on the right and left aspects of the area of re- ported pain. Flor, Turk, and Birbaumer, for example, have demonstrated exquisite specificity of emotional re- actions in the erector spinae muscles of patients with low-back pain, with little or no involvement of the facial muscles.7
Strategies associated with general relaxation are commonly used to treat the emotional component of dysfunction. Electrode placement for general relax- ation typically involves widely spaced electrodes that cross the midline. Rather than monitoring and treating one muscle group, it is better for the practitioner to monitor and treat muscular regions. Placement of widely spaced electrodes on the frontal region in- creases the probability that the practitioner will see any emotional events on the patient’s face. Widely spaced electrodes on the trapezius group allow the practitioner to see any activations of the neck and
REFERENCES
1. Loeb GE, Gans C. Electromyography for Experimentalists.
Chicago, IL: University of Chicago Press; 1986.
2. Bennett H, Kornhauser S. Assessment of general anesthesia by facial muscle electromyography (FACE). Am J Electromed.
1995;6:94–97.
3. Cram JR, Rommen DR. Skin preparation and validity of EMG scanning procedure. Biofeedback Self Regul.1989;14 (4):75–82.
4. Fridlund AJ, Cacioppo JT. Guidelines for human electro- myographic research. Psychophysiol.1986;23:567–598.
5. Taylor W. Dynamic EMG biofeedback in assessment and treatment using a neuromuscular reeducation model. In:
Cram JR, ed. Clinical EMG for Surface Recordings, II.
Nevada City, CA: Clinical Resources; 1990:175–196.
6. Cram JR. EMG muscle scanning and diagnostic manual for surface recordings. In: Cram JR, ed. Clinical EMG for Surface Recordings, II.Nevada City, CA: Clinical Resources;
1990:1–142.
7. Flor H, Turk D, Birbaumer N. Assessment of stress-related psychophysiological reactions in chronic back pain patients. J Consult Clin Psychol.1985;53(3):354–364.
8. Ettare D, Ettare R. Muscle learning therapy: A treatment protocol. In: Cram JR, ed. Clinical EMG for Surface Recordings, II.Nevada City, CA: Clinical Resources;
1990:197–234.
CHAPTER QUESTIONS
1. Which type of electrode is ideal for dynamic movement studies?
a. direct contact electrode b. cup or floating electrode c. dry electrode
d. tri-electrode
2. When bridging of electrode paste between two electrodes occurs, what effect does it have on the resulting SEMG amplitudes?
a. It quickens the response time of the SEMG signal.
b. It artificially increases the SEMG levels.
c. It artificially decreases the SEMG levels.
d. It sends the amplitude to 0.
3. Which electrode is ideal for patients who are allergic to either the paste or the adhesive collar?
a. direct contact electrode b. cup/floating electrode c. hydrogel electrode
d. percutaneous fine-wire electrode
4. Which of the following represent problems or artifacts that may be introduced into the SEMG signal by the electrode leads?
a. 60-Hz noise (the antenna effect) b. movement artifact
c. radio frequency interference d. all of the above
5. Strain relief refers to:
a. removing the weight of the electrode leads from the electrodes themselves
b. the effect of placing the muscle on stretch c. the effect on the electrode when the patient moves
through the range of motion
d. the effect of taking the muscle off of stretch 6. Site preparation for electrode placement:
a. is always recommended
b. is needed only with low-input impedance amplifiers c. is needed only with high-input impedance amplifiers d. is not needed
7. Poor electrode contact usually has what effect on the SEMG recording?
a. It artificially decreases the SEMG amplitudes.
b. It artificially increases the SEMG amplitudes.
c. It reduces the response time of the SEMG to changes in muscle function.
d. It changes values only in instruments with high input impedances.
8. When placing the SEMG electrodes for dynamic SEMG procedures, the practitioner should consider:
a. symmetry of recording electrode placement b. agonists and antagonists (myotatic units) c. the anterior compartment
d. the posterior compartment e. all of the above
9. When conducting assessments for the postural
component of muscle dysfunction, which of the following procedures yields the most complete picture?
a. muscle scanning b. dynamic SEMG protocols c. frontal SEMG recordings d. palpation examination
10. When assessing for the emotional component of dysfunction, the practitioner should:
a. place the electrodes on the facial muscles (wide-spaced frontal)
b. place the electrodes on the site of injury or pain c. place the electrodes over the zygomaticus d. both a and b
11. When conducting a general relaxation training session, it is extremely useful to:
a. use widely spaced electrodes
b. place the recording electrodes across the midline c. use closely spaced electrodes
d. place the electrodes so that they run parallel to the muscle fibers
e. both a and b
12. When placing SEMG electrodes for dynamic protocols, the practitioner should:
a. place the electrodes over the belly of the muscle fibers of interest
b. place the electrodes over the compartment of the muscle of interest
c. place the electrodes such that they avoid cross-talk from other muscles
d. all of the above
75 In the healing arts, it is commonly believed that treat- ment should naturally flow from the practitioner’s diag- nostic impressions. For surface electromyography (SEMG), this diagnosis is not the same type of medical diagnosis that is seen with intramuscular EMG studies;
these intramuscular, needle studies have to do with structure and tissue damage. With SEMG, the practi- tioner makes a functional or clinical diagnosis; instead of diagnosing tissue damage, the practitioner considers the use or misuse of muscular energy by the central nervous system. George Whatmore, one of the pioneers of SEMG, referred to this misuse of muscular energy as dysponesis, or the bad use of energy.1
As in formal diagnosis, a strong functional diagnosis re- quires the practitioner to “correctly” interpret the infor- mation collected during assessment, basing the SEMG treatment protocol upon this interpretation. To that end, this chapter focuses on the interpretation of SEMG in- formation and strategies for using SEMG to correct the observed anomaly.