Terms such as muscle tension headache reflect the traditional view that tonically elevated activity of the muscles of the head and neck are responsible for headache pain. Muscle tension itself has been considered synonymous with various forms of back pain. However, evidence suggests this concept will neither lead to an understanding of the actual etiology of these conditions, nor even to descriptions of the functional pathology that causes the pain.
For chiropractors, the importance of expertly assessing the functional state of the motor system is emphasized by studies suggesting faulty motor control is the most likely source of at least half of low back pain syndromes.4 The evidence now shows with greater clarity than ever that inflammation or injury produces specifically identified inhibited muscles. Controlled clinical studies have shown that dysfunction and pain specifically in the ankle, knee, lumbar spine, temporomandibular joint and cervical spine will produce inhibited muscles.5-16 These data indicate that the body's reaction to injury and pain is not increased muscular tension and stiffness. Instead, muscle inhibition is often more significant.
Because of Sherrington's Law of Reciprocal Inhibition, these two functional states in muscles are related.17 Sherrington's Law states that decreased activity of certain muscles leads to facilitation, and thus increased activity and tension, of their antagonist muscles. Poor motor control goes hand in hand with decreased joint stability and may be the fundamental force creating and perpetuating spinal dysfunction.9-16 Later works report that muscles predictably respond to pain, inflammation and/or injury with weakness.18-27 These researchers have demonstrated that - to use Lewit's phrase - functional pathology of the muscle system is the most common clinical finding in pain patients presenting to chiropractors and other musculoskeletal physicians.18 However, this disorder of the muscle system is routinely ignored in the diagnosis and treatment of these patients because physicians do not have a tool in their offices to diagnose it.
There is no clinical tool available for testing specific muscle strength and function as reliable, easy-to-use, inexpensive and valid as the manual muscle test (MMT).28 MMT presents a clinical strategy to assess these muscular impairments that have been shown to drive so many of the clinical conditions affecting chiropractic patients. Assessing the function of muscles with MMT pre- and post-treatment can also help assess the benefit of your therapeutic intervention. This assessment process is the basis of applied kinesiology (AK) and a family of associated chiropractic techniques that investigate muscle dysfunction using MMT.
Several hundred studies that used age- and sex-matched controls are available for review at the International College of Applied Kinesiology Web site. These studies show that the level of muscle activity is not higher than normal in most of the common musculoskeletal conditions, but actually is reduced.29 These studies are part of the reason for the demise of the hyperactivity-causality model of musculoskeletal pain. In the older hyperactivity-causality model, if "muscle tension" or "muscle hyperactivity" are pathognomonic of these conditions, EMG and maximum voluntary contraction levels should be higher in this patient population compared to other similarly matched groups.
The research instead demonstrates that pain does not cause muscles to become tonically hyperactive. The ability to contract them forcefully is reduced by pain, rather than increased. These results are more in line with the common impression that pain makes muscles difficult to use and less powerful.31
Most measurements of force output of the lower back flexor and extensor muscles when they act as agonists indicate that the maximum voluntary contraction of chronic-LBP patients is less than that of matched controls.3,29 These pain-adaptations are designed to protect the injured part of the body.30 Motor programs control the premotor nociceptive interneurons to agonist and antagonist motoneurons in a reciprocal way (Sherrington's Law), meaning that pain creates muscular weakness and hypertonicity in combination.17 Because there is a direct relationship between the tone of a muscle and the relative hypertonicity in its antagonist muscle, imbalances develop that lead to postural fatigue, structural distortion and articular pain with movement.
Dishman, et al., have shown that spinal manipulative procedures lead to an increase in central motor excitability, rather than overall inhibition.1 Specifically, there is post-synaptic facilitation of alpha-motoneurons and corticomotoneurons that may be unique to chiropractic SMT.
Previous work has demonstrated that there is an immediate strengthening effect upon the peripheral muscles after SMT.32-37 This factor has been consistently demonstrated in AK and other manipulative systems that use MMT. Measuring the effect of manipulative treatment upon the motor system can be made after every intervention. Manipulative procedures that are specifically designed to improve the function of muscles during daily life should improve spinal function and reduce disability.
Virtually every condition chiropractors face involves some form of muscle dysfunction and inhibition. MMT, when properly taught and executed, gives practitioners the unique ability to diagnose these problems. A major reason that MMT for all of the peripheral muscles should be added to standard diagnostic methods and taught in the chiropractic colleges is that most parameters of dysfunction identified in low-back and neck pain patients have not been shown to precede the pain. Rather, the dysfunction only accompanies the pain. An important exception is muscle strength, which can predict future low back and neck pain in asymptomatic individuals.9-16,38-42
The muscle weakness revolution that is now occurring in the scientific literature requires the use of a clinical tool like MMT that is uniquely designed to detect this important neuromuscular impairment in the patients whom chiropractors treat. A new paper published in Chiropractic and Osteopathy described clinical guidelines for the use of MMT, which will help perfect the precise diagnosis of this fundamental problem in our patients.43 If we miss a fundamental component of their dysfunction, treatment of complex neuromusculoskeletal disorders is that much more difficult.
- Dishman JD, Greco DS, Burke JR. Motor-evoked potentials recorded from lumbar erector spinae muscles: a study of corticospinal excitability changes associated with spinal manipulation. J Manipulative Physiol Ther, 2008 May;31(4):258-70.
- Fryer G, Morris T, Gibbons P. Paraspinal muscles and intervertebral dysfunction: part two. J Manip Physiol Ther, 2004 Jun;27(5):348-57.
- Lund JP, Donga R, Widmer CG, Stohler CS. The pain-adaptation model: a discussion of the relationship between chronic musculoskeletal pain and motor activity. Can J Physiol Pharmacol, 1991;69:683-94.
- Mannion AF, Junge A, Taimela S, et al. Active therapy for chronic low back pain: part 3. Factors influencing self-rated disability and its change following therapy. Spine, 2001 Apr 15;26(8):920-9.
- Nicholas JA, Marino M. The relationship of injuries of the leg, foot, and ankle to proximal thigh strength in athletes. Foot Ankle, 1987 Feb;7(4):218-28.
- Slemenda C, Brandt KD, Heilman DK, et al. Quadriceps weakness and osteoarthritis of the knee. Ann Intern Med, 1997 Jul 15;127(2):97-104.
- Stokes M, Young A. Investigations of quadriceps inhibition: implications for clinical practice. Physiotherapy, 1984;70:425-428.
- Spencer JD, Hayes KC, Alexander IJ. Knee joint effusion and quadriceps reflex inhibition in man. Arch Phys Med Rehab, 1984;65:171-177.
- Nummi J, Jarvinen T, Stambej U, Wickstrom G. Diminished dynamic performance capacity of back and abdominal muscles in concrete reinforcement workers. Scand J Work Environ Health, 1978;4(Suppl 1):39-46.
- Hodges PW, Richardson CA. Inefficient muscular stabilization of the lumbar spine associated with low back pain. Spine, 1996;21:2640-50.
- Hossain M, Nokes LDM. A model of dynamic sacro-iliac joint instability from malrecruitment of gluteus maximus and biceps femoris muscles resulting in low back pain. Med Hypoth, 2005;65(2):278-81.
- Zafar H. Integrated jaw and neck function in man. Studies of mandibular and head-neck movements during jaw opening-closing tasks. Swed Dent J Suppl, 2000;(143):1-41.
- Jull GA. Deep cervical flexor muscle dysfunction in whiplash. J Musculoskel Pain, 2000;8:143-54.
- Jull G, Barret C, Magee R, Ho P. Further clinical clarification of the muscle dysfunction in cervical headache. Cephalgia, 1999;19:179-185.
- Vernon HT, Aker P, Aramenko M, et al. Evaluation of neck muscle strength with a modified sphygmomanometer dynamometer: reliability and validity. J Manip Physiol Ther, 1992 Jul-Aug;15(6):343-9.
- Edgerton VR, Wolf SL, Levendowski DJ, Roy RR. Theoretical basis for patterning EMG amplitudes to assess muscle dysfunction. Med Sci Sp Exer, 1996;28:744-51.
- Brown DD, Ed. Selected Writings of Sir Charles Sherrington. Oxford: Oxford University Press, 1979:274-82.
- Lewit K. Manipulative Therapy in Rehabilitation of the Locomotor System, 3rd Edition. London: Butterworths, 1999.
- Liebenson C, Ed. Rehabilitation of the Spine: A Practitioner's Manual, 2nd Edition. Philadelphia: Lippincott, Williams & Wilkins, 2007.
- Janda V. Muscle Function Testing. London: Butterworths, 1983.
- Goodheart GJ. Applied Kinesiology Research Manuals. Detroit: 1964-1995.
- Kendall HO, Kendall FP. Posture and Pain. Baltimore: Williams & Wilkins, 1952.
- Panjabi M. A hypothesis of chronic back pain: ligament subfailure injuries lead to muscle control dysfunction. Eur Spine J, 2005 Jul 27.
- Janda V. "Muscle Strength in Relation to Muscle Length, Pain and Muscle Imbalance." In: Muscle Strength, Harms-Ringdahl K, Ed. New York: Churchill Livingstone, 1993.
- Sahrmann S. Diagnosis and Treatment of Movement Impairment Syndromes. St. Louis: Mosby, 2001.
- Bergmark A. Stability of the lumbar spine. A study in mechanical engineering. Acta Orthop Scand, 1989;230:20-4.
- Hammer WI, Ed. Functional Soft Tissue Examination and Treatment by Manual Methods, 2nd Edition. Gaithersburg, Md.: Aspen, 1999:415-45, 12, 27-33.
- Cuthbert SC, Goodheart GJ Jr. On the reliability and validity of manual muscle testing: a literature review. Chiropr Osteopat, 2007 Mar 6;15(1):4.
- International College of Applied Kinesiology. www.icakusa.com/scientificresearch.php
- Panjabi M. The stabilizing system of the spine. Part I. Function, dysfunction, adaptation, and enhancement. J Spinal Disord, 1992 Dec;5(4):383-9; discussion, 397.
- Mills KR, Edwards RH. Investigative strategies for muscle pain. J Neurol Sci, 1983 Jan;58(1):73-8.
- Shambaugh P. Changes in electrical activity in muscles resulting from chiropractic adjustment: a pilot study. J Manip Physiol Ther, 1987;10(6):300-4.
- Dishman JD, Bulbulian R. Spinal reflex attenuation associated with spinal manipulation. Spine, 2000 Oct 1;25(19):2519-24; discussion 2525.
- Suter E, McMorland G. Decrease in elbow flexor inhibition after cervical spine manipulation in patients with chronic neck pain. Clin Biomech (Bristol, Avon), 2002 Aug;17(7):541-4.
- Floman Y, Liram N, Gilai AN. Spinal manipulation results in immediate H-reflex changes in patients with unilateral disc herniations. Eur Spine J, 1997;6(6):398-401.
- Unger J. The effects of a pelvic-blocking procedure upon muscle strength: a pilot study. Chiropr Technique, Nov 1998;10(4).
- Perot D, Goubel F, Meldener R. Quantification of the inhibition of muscular strength following the application of a chiropractic maneuver. J Biophysique Biomecanique, 1986;32(10):471-4.
- Helkimo M. Studies on function and dysfunction of the masticatory system. IV. Age and sex distribution of symptoms of dysfunction of the masticatory system in Lapps in the north of Finland. Acta Odontol Scand, 1974;32(4):255-67.
- Biering-Sorensen F. Physical measurements as risk indicators for low-back trouble over a one-year period. Spine, 1984 Mar;9(2):106-19.
- Karvonen MJ, Viitasalo JT, Komi PV, et al. Back and leg complaints in relation to muscle strength in young men. Scand J Rehabil Med, 1980;12(2):53-9.
- Barton PM, Hayes KC. Neck flexor muscle strength, efficiency, and relaxation times in normal subjects and subjects with unilateral neck pain and headache. Arch Phys Med Rehabil, 1996 Jul;77(7):680-7.
- Cady LD, Bischoff DP, O'Connell ER, et al. Strength and fitness and subsequent back injuries in firefighters. J Occup Med, 1979 Apr;21(4):269-72.
- Schmitt WH, Cuthbert SC. Common errors and clinical guidelines for manual muscle testing: "The Arm Test" and other inaccurate procedures. Chiropr Osteopat, 2008;16:16.
Dr. Scott Cuthbert is the author of Applied Kinesiology Essentials: The Missing Link in Health Care (2013), and Applied Kinesiology: Clinical Techniques for Lower Body Dysfunctions (2013), the content of which forms the basis for this and subsequent articles. Dr. Cuthbert is a 1997 graduate of Palmer Chiropractic College (Davenport) and practices in Pueblo, Colo. He has published Index Medicus clinical outcome studies and literature reviews, and 50 peer-reviewed articles on chiropractic approaches.