Human Resting Muscle Tone (HRMT): Narrative Introduction and Modern Concepts

Alfonse T. Masi, MD, DR.P.H. *

Professor of Medicine and Epidemiology

University of Illinois College of Medicine at Peoria

One Illini Drive, Peoria, IL 61656, USA

Tel: +1 309 671 8428

Fax: +1 309 671 8513

Email: [email protected]

John Charles Hannon, DC

Certified Feldenkrais Practitioner

1141 Pacific Suite B

San Luis Obispo, CA 93401, USA

Tel: +1 805 542 9925

Fax: +1 805 541 2391

Email: [email protected]

Key Words: passive tone or tonus; viscoelastic; skeletal muscle; fascia; myofascial, biotensegrity

*Correspondence to: Dr. AT Masi

1 Abstract Human resting muscle studies have been performed to establish (myofascial) tone (HRMT) is the passive normal frequency distributions of degrees of tonus or tension of skeletal muscle that myofascial tone. Clinical experience derives from its intrinsic (EMG-silent) indicates that persons with certain molecular viscoelastic properties. The word symptomatic musculoskeletal conditions tone has been used to convey varying may have palpably increased resting muscle clinical and physiological features that have firmness or hardness (EMG-silent), such as led to confusion and controversy. HRMT is that of the upper trapezius in tension-type the vital low-level, passive tension, and headache, and the lumbodorsal extensors resistance to stretch that contributes (hartspann) in degenerative lumbar disc importantly to maintaining postural stability disease and ankylosing spondylitis. in balanced equilibrium positions. In contrast, co-contraction of muscle is an In summary, resting skeletal muscle tone is active neuromotor control that provides an intrinsic viscoelastic tension exhibited greater levels of tonus for increased within the body’s kinematic chains. It stabilization. Functionally, HRMT is functions inseparably from fascial (i.e. integrated with other passive fascial and myofascial) tissues and ligamentous ligamentous tensional networks of the body structures. Thus, HRMT is a passive to form a biotensegrity system. This review myofascial property which operates within aims to achieve better understandings of networks of tensional tissues, i.e., HRMT and its functional roles. biotensegrity. This passive tension is the CNS-independent component resulting from Nature is frugal and Man’s adaptations to intrinsic molecular interactions of the gravitational forces and erect postures actomyosin filaments in sarcomeric units of seemingly evolved mechanisms in skeletal skeletal muscle and myofibroblast cells. muscle tissues to economically enhance The overarching CNS-activated muscle stability. Normal passive muscle tone helps contractions generate far greater tensions maintain relaxed standing body posture with transmitted by fascial elements. minimally increased energy costs (circa 7% Interdisciplinary research on HRMT and its over supine), and often for prolonged biodynamics promises greater effectiveness durations without fatigue. Available data of clinical practitioners and productivity of infer polymorphic variations in normal investigators, which warrants priority myofascial tone. However, few quantitative attention.

2 Introduction application describing the general state of the tissues, such as vascular tone, nerve A systems level understanding of the tone, skin tone, general tone etc. Their human body is more complex than second use exclusively applied to muscle defining characteristics of isolated parts of tonus. They described it, ‘to represent the a cell or the organism. Aristotle result of a purely neural phenomena.’ This perceptively propounded, “the whole is neural focus of muscle tone was intensified greater than the sum of its parts” by the extensive experimental work of (Aristotle). Emergent concepts from Sherrington’s group (1906, 1915, 1919, & systems approach to applied research often 1947; Denny-Brown, 1929a,b). require integration of many fields of thought. We review the mainly neglected Muscle tone has received considerable area of human resting muscle (myofascial) neurophysiological attention over the years, tone (HRMT). The aim is to update but it has mainly been viewed as a current concepts and to stimulate critical manifestation of stretch reflex neuromotor discussion for better understandings in the control (Denny-Brown, 1929a,b; Walsh, future. 1992; Simons & Mense, 1998). Relatively little research has been done on resting muscle tone. In the early 20th century, Sir Life is movement and muscle has been Charles Sherrington (1852 – 1952) studied almost entirely in its activated investigated decorticated and spinal- state transected experimental specimens, rather than intact animals or humans. In his early Following Hippocrates, Claudius Galen, a work, Sherrington (1906) suggested a role second century physiologist, empiricist for skeletal muscle reflex tonus in philosopher and writer, is often considered maintaining postural attitude. Later (1915), the most important contributor to medicine. he wrote ‘a fairly literal meaning attaching He had particular interest in types of body to the term 'tonus' is, of course, mechanical movements. Galen considered muscle tone tension. In this sense it fits well the slight, as belonging to the fourth type of movement steady, enduring tension so characteristic of in which static resistance is generated; an muscles in their state of reflex tonicity.’ example being a shield held against a striking sword (Galen). Such description of Sherrington concluded that muscle tone muscle tone generated in static resistance is resulted from reflex neurogenic mechanisms more accurately described as an action, (Sherrington, 1919 & 1947), based upon his produced by muscle co-contraction and models which interrupted central inhibitory controlled by the nervous system pathways of muscle contraction. Post- (Sherrington, 1919). surgical recovery, the animals displayed generally exaggerated neurogenic reflexes. Tone and tonus [G. tonos, tone, or a tone] Stretch reflex mechanisms were overly- are general terms which have been used for generalized as the cause of all muscle tonus multiple meanings since antiquity, and often (Walsh, 1992; Simons & Mense, 1998). interchangeably. For instance, 100 years Diligent review of Sherrington's writings did ago, Fraenkel and Collins (1903) outlined not reveal a statement referencing the role of two uses. The first was a histological passive (non-reflex), mechanical,

3 viscoelastic tonicity of skeletal muscle. Even today, Sherrington’s experiments have promulgated the common belief that neurogenic reflex mechanisms are responsible for all forms of muscle tone, including resistance to slow passive stretch in fully relaxed normal persons. Many modern textbooks still consider muscle tone as entirely reflex in origin and resulting from a myotatic (a stretching) reflex in the muscle spindles.

Table 1 Papers Affirming Human Resting Muscle Tone (Chronological Sampling)*

1934 - Fenn WO, Garvey PH. J Clin Invest 13: 383-97.

1941 - Hoefer PFA. Arch Neurol Psychiat 46: 947-72.

1951 - Clemmesen S. Proc R Soc Med 44: 637-46.

1953 - Ralston HJ, Libet B. Am J Physical Med 32: 85-92.

1960 - Joseph J. Man’s Posture. Electromyographic Studies. Thomas, IL

1962 - Morris JM, Benner G, Lucas DB. J Anat 96: 509-20.

1966 - Stolov WC. Arch Phys Med Rehabil 47: 156-68.

1972 - Donisch EW, Basmajian JV. Am J Anat 133: 25-36.

1986 - Hnik P. Biomed Biochim Acta 45: S139-43.

1992 - Walsh EG. Muscles, Masses and Motion. London, Mac Keith

1992 - Davidoff RA. Neurology 42: 951-63.

1994 - Hagbarth K. Scand J Rehab Med, 30 ( Suppl ): 19-32.

1998 - Simons DG, Mense S. Pain 75: 1-17.

2007 - Loram ID, Maganaris CN, Lakie M. J Physiol 584: 661-75.

2007 - Loram ID, Maganaris CN, Lakie M. J Physiol 584: 677-92.

*Full titles in the reference list

4 Notable literature affirming human (MVC) (Mahieu et al., 2007; Gajdosik et al., resting muscle tone (Table 1) 1999). However, when calf muscle tone is measured under even more relaxed static The classical CNS-activated stretch reflex experimental conditions, it is EMG-silent, theory of muscle tone predominates in the and its inherent stiffness can maintain stance literature. However, it overlooks clinical in defined balanced posture (Loram et al., and experimental research supporting resting 2007a,b). muscle tone (EMG-silent) in intact animals and humans, as cited in Table 1 (titles are Importantly, both the subject and the tested included in the reference section). The muscle must be in a state of full relaxation absence of EMG evidence of muscle in evaluating HRMT, since its intrinsic contractile activity of normal resting muscle tension (without extraneous contractions) is (Table 1) has indicated that such clinically only about 1% maximal voluntary recognized tone is caused by intrinsic contractions (Woledge, 2003). The absence viscoelastic properties (Walsh, 1992; of such standardized relaxed testing Simons & Mense, 1998). For example, conditions has led to contradictions in Clemmesen (1951) was a pioneer exponent studies. of passive muscle tone, in both static and movement functions. He specified that Experimental research evidence for EMG-silent passive tone assists and resists passive muscle tone and its categorization active movements, contributes to synergists and antagonists, and counteracts inertia and Space limitation does not permit detailed external forces, including those of gravity. review of experimental evidence for low level tension in isolated, denervated muscle. Since the 1940’s, increased clinical use of Briefly, D. K. Hill (1968) applied slow small electromyography (EMG) has confirmed stretches (~ 0.2 % isometric length) to a that normal, fully relaxed muscles do not resting, denervated frog sartorius. He have reflex activation, being EMG-silent. inferred that a small elastic part of resting However, proper experimental conditions tension is due to interaction of thick myosin require that the subject’s positioning needs and thin actin filaments. He called the to be comfortable and in equilibrium- initial tension on small passive stretch, as balanced postures and relaxed to the fullest “short-range elastic component (SREC)”. extent. Superimposed EMG activity can The passive tension was labeled often be observed under other static or ‘filamentary resting tension (FRT)’. It was passive testing conditions, as previously estimated to be about 150g per 100g of reviewed (van der Meche & van Gijn, muscle tissue (Hill, 1968). Thus, it would 1986). Passively moved normal skeletal constitute about 1% of MVC (Woledge, muscles are also EMG-silent, when the 2003). Subsequent molecular research has subjects are fully relaxed, unlike demonstrated that myosin head cross- Sherrington’s animals. However, low-level bridging to actin filaments in muscle is the EMG activity may be observed under certain intrinsic force generator for active as well as intended passive experimental settings, as resting tension (Campbell & Lakie, 1998; when measuring resistive torque during Sugi, 2003). The components of passive or isokinetic motion of the ankle joint. Such resting, as opposed to CNS – activated or – extraneous contractile activity can amount to controlled, muscle tone are summarized in circa 2% of a maximal voluntary contraction Figure 1.

5 Figure 1

Legend to Figure Simplified components of intrinsic passive vs CNS-activated muscle tone, to help clinically differentiate the respective mechanisms causing detectable tension/stiffness (modified from Simons and Mense, 1998). Contracture, which results from pathological lesions of muscle, restricts extensibility and is considered to be EMG-silent. Terms are briefly described in Table 3, extracted from Panjabi (1992), and are included in Simons and Mense (1998). The passive resting viscoelastic tone is estimated to be circa 1 % maximum voluntary contraction (MVC), which helps maintain stability in balanced equilibrium postures (see text). The EMG-silent resting tone must be differentiated from extraneous contractions or co-contractions (EMG active) which are CNS-activated or -controlled. The passive elastic component is short-range (circa 0.2% of resting isometric muscle length). It was labeled "short-range elastic component (SREC)" by Hill (1968). Longer passive stretchers have viscoelastic physical properties. 6 Review of JBMT papers referring to right or left. Feldenkrais theorized that no muscle tone one succeeded because of an insensible turning of the body during gait towards the The concept of HRMT is novel and has not heavier side. He predicted this side to be the been well incorporated into current patient right because of the location of the heaviest assessment or management. This review is unpaired organ of the body: the liver. intended to begin a dialogue concerning resting muscle tone. We examined all past Feldenkrais (1949, 1972) noted that the issues of JBMT, and those statements standing body is most ready for translation referring to muscle tone were extracted from at short notice, if its center of gravity is relevant articles. The information was maintained at the highest possible position. integrated and synthesized in order to He also noted that practically no expenditure understand the varied viewpoints. No of energy was necessary and that this statement was found that explicitly defined minimum is drawn from potential energy. or endorsed HRMT. Also, no statement contradicted the validity or utility of HRMT. In the less than ideal body, Feldenkrais Thus, we conclude that the concept of (1949) described rigid muscles as “short and HRMT had not been formally addressed in never relax to assume their full length, and JBMT, and that it is now worthy of critical feel string-like to palpation. …” attention. He continued (1949), having stated, “Every Many general mentions were found on joint where the two members [bones] are muscle tone. However, the functional role inclined transmits a portion only of the force of resting or passive tension (EMG-silent) applied to either of them, and acts as a dash- was not critically addressed as opposed to pot, damping all transmission of mechanical CNS-activated tone or extraneous stress through the joint. The soft, wooly contractions. Notably, some authors punch of many boxers is due to faulty hip emphasized that gravity was an important carriage, and no amount of training can ever force that needed to be addressed in make the punch ‘hard’ so long as there are movements or postures. However, the springy, flexed joints, at the instant of energy efficient passive viscoelasticity of hitting.” the body was not raised as an evolutionary adaptation for maintaining balanced stability postures. The aim of this paper is to more explicitly differentiate passive from active Text Box 2: Dr. Ida Rolf’s (1896 - 1979) muscle tone and to stimulate discussion of selected quotes on tone the clinical and functional significance of HRMT. Rolf (1990a) stated that, “Man consists, more or less, of stackable units. The agents Text Box 1: Dr. Moshe Feldenkrais’ of this balance are the bones and the soft (1904-1984) selected quotes on tone tissue (myofascia). Bones determine position in space, but bones are held by soft Feldenkrais (1984) recalled a story of an tissue. When the myofascia is repositioned, Italian count challenging anyone to walk bones spontaneously reorient. When the blindfolded 300 yards across the cobbled tone of the soft tissue is balanced, there is a stones of the city’s plaza without deviating sensation of lightness in the body. The masses of head, thorax, pelvis, etc., are no

7 longer dragged out of true by their weight; Nimmo coined the term receptor tonus the structure presents less resistance and control method to describe his manual gravity can “flow through.” … therapy, and thought this allowed the nervous system to reset homeostasis with “In a human body, support is not something respect to muscle tone (Schneider 2007). solid. Support is relationship” (1990b). ... The developer of osteopathy, Andrew Still She continued (1990b), raising the question, (1897, 1899, 1910), wrote little on muscle “Could you translate this balance as tone? I tone or tonus in his three books. In a book don’t know. I don’t know what tone is in of 268 pages, Still (1899) mentioned tone in words, only in experience. I once equated it terms of the sympathetic nervous system’s with span, but I don’t know how to define role in controlling the tone of the ‘non- span. When you get span in a body, you get striate muscles tissue’. tone: when you get tone, you get span. Span Still (1915) wrote that the cause of diseases, is a spatial thing, tone is physiological. Both “can be found and does exist in the limited words refer to balanced structure in a living or excited action of the nerves that control body. Both tone and span indicate a the fluids of a part of or of the entire body. readiness to act and respond that is the My position is that the living blood swarms touchstone of a healthy body.” with health corpuscles which are carried to all parts of the body.”

Text Box 3: Chiropractic & osteopathic Other osteopathic authors more often founder’s selected concepts on tone mentioned tone. A representative example is McConnell (1902) who made 15 citations The cover of the founder’s textbook on on tone (see reference for pages). However, chiropractic, Palmer (1910) reads: ‘Text- none of his statements described HRMT. book of the science, art, and philosophy of Tone was described nonspecifically and chiropractic, founded on tone’. generally (vasomotor, arterial and intestinal tone, atrophied muscles and even the Wardwell (1992) quotes Gaucher-Peslherbe capsule of the kidney). as saying, “It was the ‘tonos’ of the Stoics on which Palmer founded chiropractic.” Structural integration (SI) Leach (2003) explains further and notes that “Palmer chose to adopt vibratory theory— Structural integration (SI) evolved from the that nerves vibrated normally at earlier teachings of Ida Rolf (Rolf, 1977) approximately 200 vibrations per minute, and is now popularly referred to as ‘rolfing’. representing the tone of the nervous system” It is a systematic program of postural … Further, “While Palmer’s concept that repatterning via connective tissue nerve vibrations create tone has obviously manipulation (Myers, 2004a,b). The focus been displaced, his hypothesis that too much of SI is on the balance of the myofascial or not enough nerve function is disease was tensional structures around the skeleton a forerunner to later accepted scientific (Myers, 2004a,b). However, mention was concepts of homeostasis” (Leach 2003). not made of HRMT and its role in helping to maintain balanced postures.

8 Principle of least effort In regard to active and resistance movements against gravity, Irvin Korr The concepts of the preceding founders on (1909-2004) was a neurophysiologist gravity and movements have led to more (Chaitow et al., 2004) who recognized that current approaches to manual and movement the musculoskeletal system had 90% of the therapy. Gravity is an unseen force of connections with the nervous system (Korr, constant direction and intensity which 1975). He indicated that our richest and influences the principle of least effort largest sensory organ is not the eyes, ears, (Hannon, 2000c), and should be considered skin, or vestibular system, but is in fact our in patient assessment and management. muscles with their related fascia (Korr, 1975; Schleip, 2003a,b). Such rich CNS Differentiating resting muscle tone from neuromotor control is essential for precise co-contractions and extraneous stimulation of muscles in active contractions contractions and movements. Notably, this exquisite CNS-controlled system is superimposed By definition, HRMT is a separate intrinsic upon the inherent passive viscoelastic component for achieving low-level energy- properties of muscle or myofascial tissues. efficient muscle tone (Abitbol, 1988). It has In a model of spine movements, Cholewicki been profoundly stated, ‘We have never & McGill (1996) and Cholewicki et al encountered poor engineering in nature' (1997) examined the theory that antagonistic (Albrecht- Buehler, 1985). Accordingly, if trunk muscle co-activation is necessary to HRMT truly exists, as we believe that it provide mechanical stability to the lumbar does (see below), then it should serve an spine around a neutral posture. According important role. Kinesiologically, to Cholewicki and McGill (1996), spine agonist/antagonist balance achieves stability stability is greatly enhanced by co- and smoother movements. Balance refers contraction of antagonistic trunk muscles, primarily to myofascial tissues on either side e.g. abdominal and extensor muscles (as also of a joint, as they are functioning in a reviewed in Liebenson, 2004b). Such co- gravity field. Balance can occur with contraction studies of spine stability in passive (resting) or actively contracting movement do not conflict with those of muscles, depending upon the resistance passive muscle tone stabilization in relaxed needed to counteract gravity or desired in balanced stance (Table 1). Cholewicki & intended actions or movements. Confirming McGill (1995) had earlier performed the principle of least effort (Hannon, biomechanical simulation studies of the 2000a,b), the body can achieve energy- relationship between muscle force and efficient, low levels of stabilization in stiffness in whole mammalian muscle. The gravity-neutral postures by the passive stiffness of skinned muscle fibers viscoelastic properties of muscle. The body approximated the relatively simple-cross- does not need to add active co-contractions, bridge theory, but a complete muscle-tendon until greater levels of mechanical stability or unit becomes complex and non-linear. This resistance movements are required. study emphasizes the importance of defining Extraneous contractions may reflect functionalities of integrated myofascial inefficient or tensed body posturing, at a networks. cost of extra energy or easier fatigueability. The osteoligamentous stability of the vertebral spine is barely sufficient to hold

9 the weight of the head (Lucas & Bresler, tension, independently of the skeletal 1961). Therefore, myofascial support of the muscular tonus (Staubesand & Li, 1997; spine is required for stability. The Staubesand et al., 1997; Schleip, 2003a,b). controversial question is how much is Quantitative parsing of the myofibroblast required by passive properties vs active tension into its passive vs active aspects will contractions under particular balanced vs require further research. unstable equilibrium circumstances. Unnecessary co-contraction of muscles, Table 2 occurring as a result of pain, anxiety or Components Governing Stability in the habit, is disadvantageous (Lyttle, 1997). Musculoskeletal System* Extraneous muscle tension of the anterior thigh often occurs in those unable to relax 1. The myofascial passive tonicity/tension (Hannon, 2006). In study of EMG- (HRMT) monitored voluntary quadriceps muscle 2. The fascial system passive network relaxation, about two thirds of the subjects 3. The osteo-ligamentous system passive could not abruptly relax at various tested component passive movement velocities (Ferris-Hood et 4. The muscular system active contractile al., 1996). response 5. The neural system control of reflex or HRMT should be considered among active contractions biomechanics that promote stability (Table 2) * Expanded from Panjabi, 1992; Lardner, 2001 According to the conventional concepts of Panjabi (1992), the following subsystems From this review, it is clear that the role of work together to promote stability: (1) passive muscle tone has not yet been central nervous subsystem (control); (2) adequately integrated into the conventional osteoligamentous subsystem (passive), and concepts of joint stability or optimal control (3) muscle subsystem (active). The fascial of movements (see below). Although system has been more recently added as a HRMT provides only circa 1% MVC, it is fourth stability component of the body, in important in balanced equilibrium. For terms of its known passive (Lardner, 2001) discussion purposes, we added HRMT as and newly recognized active myofibroblast another subsystem component governing tissues (Schleip, 2003a,b). stability in the musculoskeletal system (Table 2). Fibroblasts can transform into myofibroblasts, which contain smooth Views on muscle tone and muscle muscle actin fibers, and can therefore grouping found in JBMT actively contract. From a teleological perspective, it makes sense that an As indicated, muscle tone involves intrinsic interspersing of smooth muscle-like cells as well as CNS-activated tensional elements into fascial sheets equips the organism with (Simons & Mense, 1998 & Fig 1). Passive an accessory tension system to increase tone is the component of intrinsic muscular tonus (Schleip, 2003a,b). Fascial viscoelastic resistance of resting muscle to smooth muscle cells enable the autonomic stretch, whereas active tone is the readiness nervous system to regulate a fascial pre- with which the nervous system activates the muscle in response to stimuli (Basmajian &

10 DeLuca, 1985; Davidoff, 1993; Hagbarth, Besides resistance to passive stretch, muscle 1994; Ng et al., 1998). Hypertonicity is tone is often clinically assessed by its defined as, literally, too much muscle tone palpatory quality on compression by the (Ng et al., 1998; Simons & Mense, 1998). examiner, i.e., its pliability, firmness, or Accordingly, intrinsic hypertonicity is an hardness. Boris Chaitow added to the abnormal increase in the resistance to stretch methodology of the neuromuscular of a resting, EMG-silent muscle. In technique (NMT), by his NMT evaluation of contrast, neuromotor hypertonicity is an a 'variable pressure' application. He abnormal increase in the readiness with emphasized application which 'met and which the nervous system activates the matched' the tissues, but which did not muscle in response to stimuli (Ng et al., overcome their intrinsic tone (Chaitow, 1998). 1996). Thus, a pioneer in NMT recognized a palpatory quality of myofascial tonicity, Postural and phasic functional roles of and considered it to be important in muscles in the body have been interpreted to assessment and therapy. Another thought influence tonicity. The postural muscles are leader (Maitland, 1995) coined the considered to be those involved primarily in neologism, palintonicity (palin, Gr. again), maintenance of upright posture, while the as in the word palindrome, which refers to phasic muscles are those primarily involved the same meaning reading forward or in movement (Tunnell, 1998). Janda (1978) backward. He described a state of even tone first suggested the categorization of muscles across the various muscles and connective into `postural' (tonic) and `phasic' tissues of our structural body (Myers, 1999). (movement) classifications. It served as a useful way of conceptualizing several of his Variable relaxation of muscle tone and clinical theories (Murphy, in Bullock-Saxton effects of balance et al., 2000). Certain muscles tended to easily become tight and hyperactive, and As reviewed above, it is possible for some certain muscles tended to become inhibited people standing in comfortable balance to and underactive (Murphy, in Bullock-Saxton fully relax with no EMG evidence of muscle et al., 2000). Tightness of postural muscles activity (Basmajian & DeLuca, 1985 & is common and can initiate a cascade of Table 1). In a passively moved (flexed or changes in locomotor system function which extended) resting (EMG-silent) muscle, e.g., often lead to pain (Tunnell, 1998). biceps brachii, length does not alter muscle tone (Basmajian & DeLuca, 1985). A A clinical implication of hypertonic postural common problem, however, is that some muscles is that the body mechanics in persons are unable to relax and often are postures and movements are not optimally susceptible to increasing their muscle countering the extant forces of gravity, tension at a moment's notice (Myers, 1998; which we favor. An alternate viewpoint is Hannon, 2000b). that a muscle becomes hypertonic (increased muscle tone) or hypotonic (decreased Most often, balance is viewed as an active muscle tone), as a result of certain process, rather than in states of gravity- neurological events, not because the muscle neutral or balanced equilibrium. However, is `tonic' or `phasic' (Janda, 1978; Stokes & much of comfortable living occurs in such Young, 1984; Johansson & Sojka, 1991). balanced equilibrium, e.g., being reclined, sitting, or relaxed standing. Passive muscle

11 tone constitutes only about 1 % of maximum infrequently documented (Loram et al., voluntary contraction (MVC) ability 2007a,b). (Woledge, 2003). However, this small tension can be sufficient for stability in The biomechanics of muscle is complex and quiet, gravity-neutral stance (Loram et al., cannot be adequately reviewed in this paper. 2007a,b, and Table 1). However, selected biomechanical definitions and relevant terms were published The theoretical argument could be made that previously in JBMT (listed in Table 3) or EMG silence does not exclude CNS control elsewhere (Simons & Mense, 1998). of passive muscle tone. However, such neurophysiological control is not yet Table 3 documented, and such interpretation was not Selected Definitions Related to Physical favored by proponents of HRMT (Table 1). Properties of Muscle Tone* The degree of postural and structural balance directly influences whether only passive muscle tone is needed to maintain Stiffness: A material's resistance to stability or whether the greater CNS deformation neuromotor control is required. Further integrated EMG and myofascial tissue Strain: The amount of deformation that tensional (stiffness) research is needed. occurs as a result of the applied force Quantitation is needed of forces across specific joints that can be balanced by only Elasticity: The property of a material to passive vs active CNS-stimulated tone. return to its original form or shape when a Such quantitative studies have been done deforming force is removed across the ankle joint in quiet, relaxed

stance. They indicate that small ranges of forward tilt can be stabilized only by passive Viscosity: The measure of shear force calf muscle tone (Loram et al., 2007a,b). that must be applied to a fluid to obtain a rate of deformation. It is time dependent Standing men continuously oscillate, and their muscles are needed to correct Thixotropy: The property exhibited by displacements and prevent falling (Hannon, materials such as muscle of becoming fluid 2001a). A subtle, but important point is that when disturbed or shaken and of setting minor perturbations of balanced equilibrium, again when allowed to stand e.g., heart impulses and respirations, can be stabilized by the body’s intrinsic myofascial Viscoelasticity: The property of being elasticity (Gallasch, 1998). Such passive both elastic and viscous oscillations on Earth are relatively rapid (10 Hz). In contrast, control of the greater *Extracted from Panjabi, 1992 degree of body sway (not oscillations) is under active reflex control. Sway has a lower frequency (circa 1 Hz), required by Structural balance and achieving the long latency of proprioceptive CNS favorable postures pathways (circa 0.120 sec). Differentiation of passive oscillations vs active reflex Achievement of structural balance, and, control of standing sway is controversial and most assuredly, ease and generosity of

12 movement, are priority therapeutic ideals Myofascial - Osteoligamentous (Myers, 2004a,b). Understood in such connectivity of the musculoskeletal system statements, but not always stated, is avoidance of unnecessary co-contractions. The upright human displays a unique Also, the energy-efficient passive interdependence between the skeleton, the myofascial tone should be utilized during extra-cellular matrix (ECM) webbing, and gravity-neutral activities. The topic of interstitial fluid. The neurally-controlled posture, and how the individual uses their muscle provides the active or reflexive body is central to most bodywork and adaptation responses (Myers, 1997). We movement therapies (Hannon, 2000a). fully agree with this concept in movements Upright stance is generally considered an or in static resistance. However, in gravity- example of unstable equilibrium. However, neutral, balanced equilibrium, the passive balanced positions may be achieved in myofascial tonicity provides important which little force is needed to maintain stability to the body. The body itself seems stability (Hannon, 2006; Loram et al., to work over a continuum of structural 2007a,b). The trick of efficient postural solutions to its gravitational and mechanical adjustment is to have, be able to find, and challenges (Myers, 2001). When such actually employ, a neutral posture to which perturbations are minimal, then the low- we return after an activity (Myers, 1999). level passive myofascial viscoelasticity Achieving an easy, relaxed alignment of the (circa 1 % MVC) may be sufficient to basic body segments in gravity is a maintain stability, especially in static, fundamental body-mind integration tool balanced postures. With movement or (Myers, 1999). increased loading, the active muscle subsystem may then be more likely required Persons may, for various reasons, assume (Cholewicki & McGill, 1995 & 1996; overly stiffened postures that require co- Cholewicki et al., 1997). contractions (i.e., “military” stance). However, with education and rehabituation, Myofascial continuities are key to global natural relaxed posture gradually emerges pattern assessment in bodywork and (i.e., “at ease”). This posture conforms to movement treatments. Five major lines the body's response to gravity (Latey, 1996), were originally proposed and their clinical and can be maintained mainly by passive implications were earlier discussed (Myers, muscle tone (Table 1). Thus, the concepts 1996). More recently, an alternate version of postural stability and movement was developed, based on longitudinal instability are integral to modern myofascial continuities (Myers, 2004a,b). musculoskeletal care (Liebenson, 2004a,b). The lead author of this review has focused Unstable equilibrium, as a form of dynamic primarily on the muscle-ligament-fascia response, was previously reviewed (Hannon, systems required to stabilize the pelvis by 2001b). Additional research is needed on compressing the SI joints (Masi et al., the role of passive resting myofascial tone in 2003a,b & 2005). The concept of form and helping to achieve and maintain stability in force closure of the pelvis was developed by equilibrium postures and flexibility in Andry Vleeming (1990a,b) and his peripheral joint movements (Magnusson et associates (Lee, 2004). It permits better al., 2001). understanding of clinical conditions which result from insufficient or excessive pelvic (or other joint) stability, due to respective

13 hypo- or hyper- myofascial tonicity (Vleeming, 2004). Proper assessment of each muscle condition requires a different treatment approach (Ng Biotensegrity as a model of the body’s et al., 1998). Accepting the biotensegrity balanced tensional forces model, tensional alterations of myofascial tissues in a particular patient could be hypo The body is a structure that depends on the or hyper in any particular region. In the balance of tensional forces to maintain its past, emphasis has been given to painful stability (Myers, 1999). Such structural disuse and weakening of muscle. Less model has isolated compression elements attention was given to hypertonicity as (bones) within a balanced ocean of tensional contributing to painful limitation of motion members (myofascial). The model was and secondary weakening. More recent popularly dubbed 'tensegrity' (a contraction research suggests group aerobic and of “tensional integrity”) structures by Fuller stretching classes are as useful (1975). This architectural concept was symptomatically as modern active based upon earlier Kenneth Snelson’s physiotherapy, and as effective as muscle smaller art sculptures and larger closed strengthening or coordination methods using structural systems training devices (Adams et al., 2002). We (http://www.nlm.nih.gov/exhibition/tour/tree propose that abnormal alterations in HRMT i.html). The term was adapted to our human may be an overlooked mechanical factor in a body as a ‘biotensegrity’ structure (Robbie, number of non-degenerative spinal 1977; Ingber, 1998; Oschman, 2000; Levin, conditions and deserve greater clinical 2002). It incorporates not only the assessment. macroanatomical tissues, but also the subcellular fibrillar and micro-tubular Current concepts of myofascial trigger structures (Ingber, 2003). Within such points (MTrPs) as related to HRMT organic structure and tensional continuity of the body, the role of HRMT can be more Expressed concepts of HRMT pertain to clearly understood. Specifically, it is the pain-free healthy subjects without important motor generator to maintain myofascial tissue restrictions in active or pretensing and low-level stabilizing passive movements. Yet, evolving research functions (see Text Box). on myofascial pain syndromes (MPS) and their hallmark trigger point (TrP) clinical Clinically, HRMT is subtle to document and indicator may offer basic and clinical clues the concept has not received sufficiently to factors influencing HRMT. Simply critical attention. Nevertheless, one described, MPS are regional pain disorders important recognized property of healthy associated with a hypersensitive palpable muscle tissue is its extensibility, or the nodule (TrP) in a taut band of skeletal ability to lengthen (Tunnell, 1998). Passive muscle (Simons et al., 1999a). A snapping tension (“tone”) cannot be documented, palpation of the involved muscle area can unless EMG-silence is confirmed. reveal an induration (“taut band”) which Clinically, proper evaluation of muscle tone elicits a local twitch response (LTR) needs maximal relaxation of the patient in a (Simons et al., 1999b; Rivner, 2001). In comfortable gravity-neutral posture for the addition, restricted ranges of motion are practitioner's assessment of end-feel and often found in MPS. positioning (Tunnell, 1998).

14 Questions about MPS and TrPs that may be episodic headaches into the chronic relevant to concepts of normal HRMT symptomatic form (Ashina S et al., 2005). include: (1) mechanisms causing the “taut band”; (2) whether local or central factors The new magnetic resonance imaging (MRI) control tension in the focal tender areas (as technique - magnetic resonance elastography well as influencing surrounding muscle (MRE) – was recently used to quantitatively often perceived as feeling stiff), and (3) the explore stiffness of taut bands in a patient EMG activity of focal points and with MPS (Chen et al., 2007). The surrounding subjectively tight muscles. methodology is based upon shear waves Although definitive answers to these generated by a vibrator bar firmly pressed questions on MPS and TrPs are not yet on the subject’s skin traveling more rapidly available, their current concepts and basic in stiffer than softer tissues. In the MPS research can help generate hypotheses and patient, stiffness of the taut band was greater investigations pertinent to HRMT. than that of surrounding musculature, and more so than was found in the control Focal nodularities (TrPs) within taut bands subject. Although the study was exploratory can occur following muscle injury or (Chen et al., 2007), findings support clinical repetitive strains in susceptible subjects. observations and concepts of MPS and TrPs. One suggested mechanism is focal ischemia This methodology may be useful in future (“energy crisis component”) and calcium measurements of objective stiffness of release in contracted sarcomeric units HRMT. (Simons et al., 1999c; Simons, 2008). This concept could account for the absence of In other recent studies, microdialysis motor unit action potentials in the palpable catheters (Ashina M et al., 2003) or fine taut band of the TrP when the muscle is at gauge needles (Shah et al., 2005 & 2008) rest (Simons et al., 1999c). However, were used to sample interstitial fluid precise and sensitive needle EMG concentrations of inflammatory mediators in recordings from TrPs revealed occurrences tender points or myofascial trigger points of low voltage spontaneous activity (MTrPs) using microanalytic techniques. In (“endplate noise”) in some reports (Hubbard the controlled study of tender points in & Berkoff, 1993; Rivner, 2001; Kuan et al., CTTH patients (Ashina M et al., 2003), no 2008), but not in another (Durette et al., difference was found in resting 1991). In the chronic tension-type headache concentrations of inflammatory mediators or (CTTH) form of MPS, spontaneous EMG metabolites between patients and controls activity of muscles about TrPs was not during rest and static exercise. These data greater than in healthy matched control suggest that tender points in CTTH are not subjects (Couppé et al., 2007). In another sites of ongoing inflammation. However, in study of CTTH patients, muscle tenderness the controlled studies of TrPs, at which a as well as objective hardness were also LTR could be elicited at a standardized greater than in control subjects (Ashina M et location in the upper trapezius muscle, al., 1999). The above findings suggest that concentrations of multiple analytes were TrPs and surrounding muscle stiffness are significantly higher in the milieu of active local manifestations (Simons & Mense, than latent TrPs, and more so than in normal 1998), rather than CNS reflex mediated subjects (Shah et al., 2005 & 2008). phenomena. However, increased sensory excitability of the CNS may transform

15 These latter data support a concept of components are united to form combined chemical mediators being released into the myofascial units (Chaitow, 2006). local tissue milieu of active TrPs. To determine whether local ischemia Within this rapidly developing scientific contributes to this process (Simons et al., field, the integrated function of muscle 1999, pp 71-72) or a spinal cord level reflex needs to also be actively investigated as a related to LTR (Hung et al., 1995) will myofascial complex. Such concept has not require further investigations. Currently, the previously been well explored under passive multiple chemical mediators studied above states (static or kinetic), as opposed to the (Ashina M et al., 2003; Shah et al., 2005 & active contractile transmission of forces. 2008) do not seem to be important Promising clinical and research opportunity determinant factors in presented concepts of may be expected from critical attention to HRMT. Also, the newly applied MRE and better understanding of HRMT. technique (Chen et al., 2007) may provide quantitative validation for alterations or polymorphisms in HRMT. Acknowledgments The 2007 International Fascia Congress and interface with HRMT We thank Jessica Debis for her invaluable technical assistance in completing this That landmark Fascia Congress (2007) manuscript, Dr. Sam Betts and Profs. Jacek illustrated that fascia is the soft tissue Cholewicki, Diane Lee, and Robert Schleip component of the connective tissue system for their expert critiques of the manuscript. that exists throughout the human body. It Support for this project was provided by the forms a whole-body, three-dimensional cell Department of Medicine, University of and extra cellular matrix of support, Illinois College of Medicine of Peoria, and a continuity, and communication (Chaitow, grant from the MTM Foundation. 2006). Importantly, fascial tissues are connected to and integrated with the musculoskeletal system to provide stability and effect movements. Fascial and muscular

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