By: Christopher Kent, DC
Objective Assessment of the Relationship Between Lower Extremity Abnormalities and Paraspinal Muscle Function Using Surface Electromyography
Physical, chemical, and emotional stress may result in spinal problems, including vertebral subluxation. A common cause of physical stress is aberrant posture due to structural asymmetry in the lower extremity. Chronic physical stress caused by leg length inequality, pronation, inversion, or eversion of one or both feet leads to altered posture. The body is forced to compensate through the muscular system.
Electromyography (EMG) is the technique of recording electric potentials associated with muscular contraction. Electrodes may be inserted in the muscle being monitored, or surface electrodes may be placed on the skin overlying the muscles being studied. When surface techniques are employed, the procedure is abbreviated “sEMG.” Surface and inserted electrode techniques are not interchangeable. Inserted electrode methods are frequently used to evaluate specific nerve roots, while surface electrode procedures provide information concerning groups of muscles working together.
In Chiropractic practice, surface electrode techniques provide objective, quantitative information. Paraspinal sEMG scans, taken in concert with other examination findings, may be helpful in evaluating the following:
- Asymmetrical contraction
- Areas of muscle splinting
- Severity of the condition
- Aberrant recruitment patterns
- Effects of orthotic interventions
- Responses to dysafferentation
- Responses to Chiropractic adjustment
Decades of research by independent investigators show that surface electrode electromyography exhibits very good to excellent test-retest reliability. Spector conducted a study at New York Chiropractic College which yielded correlation coefficients ranging from 0.73 and 0.97. Komi and Buskirk compared the test-retest reliability of surface electrodes vs. needle electrodes in the deltoid muscle.1,2 The average test-retest reliability for surface electrodes was 0.88 compared to 0.62 for inserted electrodes.
Other investigators have evaluated the reliability of surface electrode techniques using hand-held electrodes. This method is referred to as surface EMG scanning. Thompson et. al. of the Mayo clinic found that the scanning electrode technique correlated well with the “gold standard” of attached electrode technique.3 Cram et. al. evaluated the reliability of surface EMG scanning in 102 subjects in the sitting and standing positions.4 The authors concluded, “With adequate attention given to skin preparation, EMG sensors held in place by hand with a light pressure provide reliable results.”
In a review of surface EMG, Lofland et al. state that “Recent methodologically sound research has shown modern multichannel surface EMG to be reliable and valid.”5
A study examining surface EMG reliability was conducted at the NZCA School of Chiropractic in New Zealand.6 The study examined the results of Chiropractic care provided by 19 Chiropractic interns to 30 patients in a teaching clinic. The equipment used was an Insight 7000 Subluxation Station. The investigators stated, “Under the conditions of this study, it is concluded that SEMG is an objective measure of change which can be used as an assessment of patient progress.”
The clinical utility of the procedure may be evaluated by determining the ability of the test to perform up to the standards predicted by a theoretical model or construct.7 In the case of sEMG, the assumption is made that significant changes in sEMG activity will occur following Chiropractic adjustment, and that significant changes will not be observed in controls.
Shambaugh conducted a controlled study where surface electrodes were used to record paraspinal sEMG activity pre- and post-Chiropractic adjustment.8 Shambaugh concluded, “Results of this study show that significant changes in muscle electrical activity occur as a consequence of adjusting.” In the osteopathic literature, Ellestad et. al. conducted a controlled study which found that paraspinal sEMG activity decreased in patients following osteopathic manipulation.9 Such changes were not observed in controls in either study. Therefore, these studies support the construct validity of paraspinal sEMG as an outcome assessment for Chiropractic adjustment.
Paraspinal Scanning Technique
Protocols and normative data for paraspinal sEMG scanning have been published in the refereed literature.10 Hand held electrodes are applied to the skin of the patient overlying the spine at 15 paired sites. EMG signals are measured in microvolts (millionths of a volt). A computer analyses these signals, and compares them to a normative data base. In the interpretation of sEMG scans, two factors are considered:
- Amplitude. This refers to the signal level in microvolts. The higher the signal level, the greater the extent of the paraspinal muscle activity. By comparing these readings to a normative database, elevated or decreased signals can be identified.
- Symmetry. This refers to a comparison of the left side to the right side.11
Postural Disturbances and Surface EMG
Posture is defined as distribution of body mass in relation to gravity over a base of support. Kuchera wrote, “Postural homeostatic lessons are learned gradually by the central nervous system from visual and proprioceptive input as the individual grows and develops… The nature of postural compensation is to react to a disturbance of posture with change throughout the remaining somatic tissues.”12
Postural changes are mediated by receptors, which monitor the dynamics of the internal and external environment, and the relationship of the individual with the environment. The receptor systems that may contribute to postural alteration include:
- Vestibular apparatus
- Joint mechanoreceptors
- Disc mechanoreceptors
- Golgi receptors
Asymmetrical paraspinal sEMG activity is frequently seen in cases where adaptive strategies to lower extremity stresses are present. This, in turn, often results in vertebral subluxation. If vertebral subluxation results in further aberrant afferent input to the CNS, a “vicious cycle” is established. Such individuals often do not “hold” their adjustments, and sEMG patterns tend to recur.
Historically, aberrant posture has been associated with a variety of health-related conditions. Jenness cites three studies relating posture to general health.13 Kuhns suggested that poor posture was associated with many pathological processes, and that good posture could prevent disease processes.14 Thompson suggested that many conditions could be “cured” by postural correction.15 Garner proposed that proper posture aids in “minimizing fatigue” and “building resistance to infection.”16
More recent writings have related postural aberrations to increased susceptibility to sports-related injuries.17–21 Alterations in posture have also been associated with adverse mechanical tension on the spinal cord and vertebral subluxation.22
Clinical strategies must be developed to minimize the adverse effects of stressors that result in recurring patterns of vertebral subluxation. If the source is leg length inequality, pronation, inversion, or eversion of one or both feet, custom orthotics, such as Foot Levelers’ functional orthotics, may enable the body to develop paraspinal muscle responses which minimize the recurrence of subluxation patterns.
Foot Levelers’ sEMG Evaluation
Foot Levelers, Inc. and the Chiropractic Leadership Alliance have collaborated to produce special software for the Insight Subluxation Station. This software facilitates the Foot Levelers evaluation, and the ordering process. The Foot Levelers module provides:
An analysis of surface EMG muscle imbalances to identify those patients that might benefit from an examination of foot posture.
- Automated data entry for the results of the foot exam.
- Automated report of findings for the foot exam.
- Automated Foot Levelers product information reports, including doctor-controlled patient pricing.
- Automated Foot Levelers order form generation for patient and doctor.
- Automated Foot Levelers order form generation for patient and doctor.
Employing surface EMG as part of the Foot Levelers evaluation provides the doctor with objective evidence, which facilitates clinical decision making. Furthermore, the color reports and product pieces enhance patient compliance through education.
- Spector B. Surface electromyography as a model for the development of standardized procedures and reliability testing. J Manip Physiol Ther 1979; 2(4):214.
- Komi P, Buskirk E. Reproducibility of electromyographic measurements with inserted wire electrodes and surface electrodes. Electromyography 1970; 10:357.
- Thompson J, Erickson R, Offord K. EMG muscle scanning: stability of hand-held electrodes. Biofeedback Self Regul 1989; 14(1):55.
- Cram JR, Lloyd J, Cahn TS. The reliability of EMG muscle scanning. Int J Psychosomatics 1994; 41:41.
- Lofland KR, Mumby PB, Cassisi JE, et al. Assessment of lumbar EMG during static and dynamic activity in pain-free normals: implications for muscle scanning protocols. Biofeedback and Self-Regulation 1995; 20(1):3.
- Kelly S, Boone WR. The clinical application of surface electromyography as an objective measure of change in the Chiropractic assessment of patient progress: a pilot study. Journal of Vertebral Subluxation Research 1998; 2(4):175.
- Patrick DL, Deyo RA. Generic and disease-specific measures in assessing health status and quality of life. Med Care 1989 (Mar); 27(3 Suppl):S217.
- Shambaugh P. Changes in electrical activity in muscles resulting from Chiropractic adjustment: a pilot study. J Manip Physiol Ther 1987 (Dec); 10(6):300.
- Ellestad S, Nagle R, Boesler D, Kilmore M. Electromyographic and skin resistance responses to osteopathic manipulative treatment for low-back pain. JAOA 1988; 88(8):991.
- Kent C, Gentempo P. Protocols and normative data for paraspinal EMG scanning in Chiropractic practice. Chiropractic 1990 (Oct); 6(3):64.
- Kent C. Instrumentation and imaging. In: Masarsky CS, Todres-Masarsky M. Somatovisceral Aspects of Chiropractic: An Evidence-based Approach. New York: Churchill Livingstone, 2001.
- Kuchera ML, Kuchera WA. General postural considerations. In: Foundations for Osteopathic Medicine. Baltimore: Williams and Wilkins, 1997.
- Jenness ME. The role of thermography and postural measurement in structural diagnosis. In: Goldstein M (ed.). The Research Status of Spinal Manipulative Therapy. DHEW Publication No. (NIH) 76-998. 1975.
- Kuhns JG. Diseases of posture. Clin Orthop 1962; 25:64.
- Thompson J. The erect posture. Lancet 1922 (Jan. 14); 1:107.
- Garner JR. Posture and fatigue. International Journal of Medicine and Surgery 1932 (Jan); 45:27.
- Watson AWS. Sports injuries related to flexibility, posture, acceleration, clinical defects, and previous injury, in high-level players of body contact sports. Int J Sports Med 2001; 22:222.
- Shambaugh JP, Klein A, Herbert JH. Structural measures as predictors of sports injury in basketball players. Med Sci Sports Exercise 1991; 23:522.
- Powers CM, Maffucci R, Hampton S. Rearfoot posture in subjects with patello-femoral pain. J Orth Phys Ther 1995; 22:155.
- Watson AWS. Sports injuries in footballers related to defects in posture and body mechanics. J Sports Phys Med Fitness 1995; 35:289.
- Cowan DN, Jones BH, Frykman PN. Lower limb morphology and risk of overuse injury among male infantry trainees. Am J Sports Med 1996; 24:945.
- Breig A. Adverse Mechanical Tension in the Central Nervous System. New York: Wiley and Sons, 1978.
About the Author
Christopher Kent, DC, is co-founder of the Chiropractic Leadership Alliance. A 1973 graduate of Palmer College of Chiropractic, Dr. Kent has been the recipient of many honors, including ICA Chiropractor of the Year. He was named Chiropractic Researcher of the Year by the ICA and WCA. A contributing author to textbooks, peer-reviewed journals, and popular publications, he is well known throughout the Chiropractic profession.