Evidence suggests measurable muscular inhibition (weakness) is associated with injury, inflammation and pain, as reviewed in my recent four-part series in this publication.1-4 This evidence is part of the rationale for the chiropractic physician's use of the manual muscle test (MMT) for the assessment of muscular inhibition in our patients. Muscular imbalance is the combination of weakness and hypertonicity (tightness); however, there are differing approaches as to the diagnosis and treatment of these muscular imbalance phenomena that are a fundamental component for patients with manipulable disorders.
The voluntary skeletal muscle system is the largest single organ in the body. It measures in at over 40 percent of body weight and is maintained in a sophisticated state of balance and coordination throughout a wide range of postures and activities. The muscles are at once the source and the recipient of the greatest neural activity in the body. This includes sensory and motor activity, segmental and cerebral pathways, plus autonomic activity in relationship to the metabolic, visceral, and circulatory demands required during human movement.
The focus of treatment for muscular imbalance is where the Goodheart and Janda models divide. Goodheart and Janda agreed that the muscles are in fact "the most exposed part of the nervous system." Muscle imbalance therefore brings us back to the nervous system, which is at the core of all human activity - this is where D.D. Palmer started from in the first place.
George J. Goodheart Jr., DC (1918-2008) and Vladimir Janda, MD (1923-2002) influenced generations of practitioners spanning many disciplines. One difference between Goodheart's approach (a chiropractor) and Janda's (a physical therapist) is that muscle inhibitions are identified and treated first with chiropractic manipulative therapy (CMT). In agreement with the literature cited in previous articles, muscle inhibition is seen as an etiological factor and/or common co-factor in neck, low back, and extremity pain and dysfunction.1-4, 5
Sherrington's law of reciprocal innervation states that muscle inhibition usually generates hypertonicity/tightness in antagonist muscles, and that the relationship between weak and tight muscles is reciprocal, with inhibition producing the same influence on their antagonist muscles as tightness. Sherrington advises that "Knowledge of reflex inhibition equally with that of reflex excitation is essential for the study of nervous co-ordination."6 This means that abnormal muscle inhibition is as neurologically important as over-facilitation in patients with pain and dysfunction.
In fact, Lund and others have confirmed Sherrington's early insights, showing that inhibition is frequently found in muscles resulting from injury, inflammation or pain and that the inhibition or weakness leads to reciprocal facilitation of its antagonist(s) and aberrant behavior of its synergist(s).1-4, 7 It is also true that hypertonicity in a muscle leads to reciprocal inhibition of its antagonist(s) and aberrant behavior of its synergist(s).8 This is the reciprocity of Sherrington's Law, with due respect paid to both the Goodheart and Janda models of diagnosis and treatment for muscular imbalance.
Goodheart's model is the one used by members of the chiropractic profession who employ the MMT for diagnosis of neuromusculoskeletal dysfunction.9-11 Inhibited muscles found in the chiropractic setting are capable of spontaneous strengthening when the inhibitory reflex is identified and remedied (most commonly through joint or soft-tissue manipulation).
In Janda's model, Sherrington's Law of reciprocal innervation operates primarily in one direction: Muscle hypertonicity/tightness/spasm generates inhibition in its antagonists, and so spasm is treated first. For this reason, muscle spasm and tightness are considered the etiological factors of articular dysfunction. In Janda's approach, hypertonic muscles are treated with physiotherapeutic means such as massage, stretching, proprioceptive neuromuscular facilitation, electrotherapy and other methods that do not usually include CMT.12-13 In Janda's classic text on MMT, there is little mention of spinal or other joint manipulation options for the muscle inhibitions found, and no correlations are observed between manipulative corrections (or cranial, meridian, nutritional, or psychological treatments) for specific muscle inhibitions.8
In Janda's model, the inhibited (weak) muscles are treated with exercise, rocker boards, wobble boards, balance shoes, and mini trampolines, among other strategies. The principles of this physical therapy approach to muscular imbalances were based on the work of Bobath and Bobath, who developed physiotherapy programs for children with cerebral palsy.14
It is of major concern that patient compliance and participation is poor for exercise programs. Most rehabilitation, stretching, and exercise programs report a reduction in patient participation (even when the individuals felt that the effort was producing benefits).15 Correcting muscle inhibitions with remedial exercise is quite time-consuming, and patients are remarkable in how incorrectly they perform their exercises. Although chiropractors employ exercise and rehabilitation programs in their treatment of patients, they focus their unique training and skills to provide CMT for correction of neurological inhibitions. Furthermore, articular dysfunctions that produce muscle inhibition in patients will not be effectively addressed with exercise, stretching, and other non-manipulative modalities.
Janda asserted throughout his remarkable career that postural muscles tend to be short and tight and usually hypertonic. However, the current literature does not always agree with Janda's classification of which muscles are "postural" or "phasic."16 Janda's conception that postural muscles tend to be tight and phasic muscles tend to be weak is too restrictive, as shown by many studies that suggest postural muscles are so often inhibited in physical disturbances, especially low back and neck pain.1-4, 17 Muscle fiber types (tonic and phasic, and slow-twitch and fast-twitch) are not fixed and evidence shows the potential for adaptability of muscles based on use and need, so that muscle fibers can be transformed from slow twitch to fast twitch and vice versa.18
Naming the muscle category and then treating the category is equivalent to giving all patients a general adjustment, or the same all-purpose multivitamin pill.
It is the clinical experience of manual muscle testers that muscle imbalances relate primarily to the individual patient's adaptations to specific injuries and stresses, rather than to any properties of these muscles to be either hypotonic or hypertonic as a rule. If a muscle becomes hypotonic or hypertonic, this occurs as a result of a lifetime of adaptive neurological events in a patient's history, and not because a particular muscle is "postural" or "phasic." The fact that postural muscles frequently show inhibition on MMT assessment is more in line with the common impression that pain makes muscles difficult to use and less powerful.19
There is considerable variability in the changes of muscle activity between individuals with neck pain, as demonstrated by the large standard deviation of EMG data.2, 20 Edinger as well as Strong showed that individuals with leg-length inequality who placed their feet in a normal position a few inches apart showed substantial individual variations in the standing EMG.21-22
In the Goodheart model, if muscle inhibition is caused by a manipulable articular or soft-tissue disorder, then the inhibited muscle's response to the proper CMT will be immediate and the tight antagonist muscles will relax. This brings about postural balance on visual inspection and corrects the positive MMT findings, both of which are evidence of the muscle imbalance phenomena.
A risk with Janda's model of muscle dysfunction is that practitioners may expect to find set changes to occur and fail to adequately assess the patient's genuine state. This can result in poor treatment outcomes. Every muscle that is part of an articular and postural dysfunction (or part of a kinematic chain of muscular dysfunction) must be specifically assessed for strength, coordination, ease of use, length and tone, no matter what model you follow clinically.
Although the distinctions between hypotonic and hypertonic muscles (including Janda's upper- and lower-crossed syndromes) can usefully assist the clinician, they are not cast in stone. Diagnosis of muscular imbalances underlying articular dysfunctions must be refined to reveal the subtleties of the muscle system's reactions to injury, pain, altered use and pathology in the particular patient under study.
Goodheart points out that muscular adaptation can involve a wide variety of influences (structural, chemical and mental).9 The chiropractor therefore must keep in mind that what is presented and observed in a patient with muscle imbalances may represent only the acute problems that brought the patient in for care, which have evolved out of chronic adaptive patterns. Discovering the core of the problem and diagnosing the treatable obstacles to normal function involves patience, adaptability and skill; and if you are using chiropractic hands-on treatment methods, the correct model of muscle imbalance helps.
Experienced clinicians agree that unpredictability and individuality are the rule where muscular compensations are concerned, especially when recent adaptations are added onto chronic adaptation patterns in the typical patient. In the case of the muscle imbalance phenomenon, this should lead clinicians to evaluate individual muscles in individual humans with the MMT. In agreement with previous literature, muscle inhibitions will be found to be major generators of the disorders chiropractors treat in their patients.
References
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