Physiology ReviewHuman resting muscle tone (HRMT): Narrative introduction and modern concepts
Introduction
A systems level understanding of the human body is more complex than defining characteristics of isolated parts of a cell or the organism. Aristotle perceptively propounded, “the whole is greater than the sum of its parts” (Aristotle). Emergent concepts from systems approach to applied research often require integration of many fields of thought. We review the mainly neglected area of human resting muscle (myofascial) tone (HRMT). The aim is to update current concepts and to stimulate critical discussion for better understandings in the future.
Section snippets
Life is movement and muscle has been studied almost entirely in its activated state
Following Hippocrates, Claudius Galen, a second century physiologist, empiricist philosopher and writer, is often considered the most important contributor to medicine. He had particular interest in types of body movements. Galen considered muscle tone as belonging to the fourth type of movement in which static resistance is generated; an example being a shield held against a striking sword (Galen). Such description of muscle tone generated in static resistance is more accurately described as
Notable literature affirming human resting muscle tone (Table 1)
The classical CNS-activated stretch reflex theory of muscle tone predominates in the literature. However, it overlooks clinical and experimental research supporting resting muscle tone (EMG-silent) in intact animals and humans, as cited in Table 1 (titles are included in the reference section). The absence of EMG evidence of muscle contractile activity of normal resting muscle (Table 1) has indicated that such clinically recognized tone is caused by intrinsic viscoelastic properties (Walsh, 1992
Experimental research evidence for passive muscle tone and its categorization
Space limitation does not permit detailed review of experimental evidence for low-level tension in isolated, denervated muscle. Briefly, Hill (1968) applied slow small stretches (0.2% isometric length) to a resting, denervated frog sartorius. He inferred that a small elastic part of resting tension is due to interaction of thick myosin and thin actin filaments. He called the initial tension on small passive stretch, as “short-range elastic component (SREC)”. The passive tension was labeled
Review of JBMT papers referring to muscle tone
The concept of HRMT is novel and has not been well incorporated into current patient assessment or management. This review is intended to begin a dialogue concerning resting muscle tone. We examined all past issues of JBMT, and those statements referring to muscle tone were extracted from relevant articles. The information was integrated and synthesized in order to understand the varied viewpoints. No statement was found that explicitly defined or endorsed HRMT. Also, no statement contradicted
Structural integration (SI)
Structural integration (SI) evolved from the earlier teachings of Ida Rolf (Rolf, 1977) and is now popularly referred to as ‘rolfing’. It is a systematic program of postural repatterning via connective tissue manipulation (Myers, 2004a, Myers, 2004b). The focus of SI is on the balance of the myofascial tensional structures around the skeleton (Myers, 2004a, Myers, 2004b). However, mention was not made of HRMT and its role in helping to maintain balanced postures.
Principle of least effort
The concepts of the preceding founders on gravity and movements have led to more current approaches to manual and movement therapy. Gravity is an unseen force of constant direction and intensity which influences the principle of least effort (Hannon, 2000c), and should be considered in patient assessment and management.
Differentiating resting muscle tone from co-contractions and extraneous contractions
By definition, HRMT is a separate intrinsic component for achieving low-level energy-efficient muscle tone (Abitbol, 1988). It has been profoundly stated, “We have never encountered poor engineering in nature” (Albrecht-Buehler, 1985). Accordingly, if HRMT truly exists, as we believe that it does (see below), then it should serve an important role. Kinesiologically, agonist/antagonist balance achieves stability and smoother movements. Balance refers primarily to myofascial tissues on either
HRMT should be considered among biomechanics that promote stability (Table 2)
According to the conventional concepts of Panjabi (1992), the following subsystems work together to promote stability: (1) central nervous subsystem (control); (2) osteoligamentous subsystem (passive), and (3) muscle subsystem (active). The fascial system has been more recently added as a fourth stability component of the body, in terms of its known passive (Lardner, 2001) and newly recognized active myofibroblast tissues (Schleip, 2003a, Schleip, 2003b).
Fibroblasts can transform into
Views on muscle tone and muscle grouping found in JBMT
As indicated, muscle tone involves intrinsic as well as CNS-activated tensional elements (Simons and Mense, 1998; Figure 1). Passive tone is the component of intrinsic viscoelastic resistance of resting muscle to stretch, whereas active tone is the readiness with which the nervous system activates the muscle in response to stimuli (Basmajian and DeLuca, 1985; Davidoff, 1992; Hagbarth, 1994; Ng et al., 1998). Hypertonicity is defined as, literally, too much muscle tone (Ng et al., 1998; Simons
Variable relaxation of muscle tone and effects of balance
As reviewed above, it is possible for some people standing in comfortable balance to fully relax with no EMG evidence of muscle activity (Basmajian and DeLuca, 1985; Table 1). In a passively moved (flexed or extended) resting (EMG-silent) muscle, e.g., biceps brachii, length does not alter muscle tone (Basmajian and DeLuca, 1985). A common problem, however, is that some persons are unable to relax and often are susceptible to increasing their muscle tension at a moment's notice (Myers, 1998;
Structural balance and achieving favorable postures
Achievement of structural balance, and, most assuredly, ease and generosity of movement, are priority therapeutic ideals (Myers, 2004a, Myers, 2004b). Understood in such statements, but not always stated, is avoidance of unnecessary co-contractions. Also, the energy-efficient passive myofascial tone should be utilized during gravity-neutral activities. The topic of posture, and how the individual uses their body is central to most bodywork and movement therapies (Hannon, 2000a). Upright stance
Myofascial–osteoligamentous connectivity of the musculoskeletal system
The upright human displays a unique interdependence between the skeleton, the extra-cellular matrix (ECM) webbing, and interstitial fluid. The neurally controlled muscle provides the active or reflexive adaptation responses (Myers, 1997). We fully agree with this concept in movements or in static resistance. However, in gravity-neutral, balanced equilibrium, the passive myofascial tonicity provides important stability to the body. The body itself seems to work over a continuum of structural
Biotensegrity as a model of the body's balanced tensional forces
The body is a structure that depends on the balance of tensional forces to maintain its stability (Myers, 1999). Such structural model has isolated compression elements (bones) within a balanced ocean of tensional members (myofascial). The model was popularly dubbed ‘tensegrity’ (a contraction of ‘tensional integrity’) structures by Fuller and Loeb (1975). This architectural concept was based upon earlier Kenneth Snelson's smaller art sculptures and larger closed structural systems (//www.nlm.nih.gov/exhibition/tour/treei.html
Current concepts of myofascial trigger points (MTrPs) as related to HRMT
Expressed concepts of HRMT pertain to pain-free healthy subjects without myofascial tissue restrictions in active or passive movements. Yet, evolving research on myofascial pain syndromes (MPS) and their hallmark trigger point (TrP) clinical indicator may offer basic and clinical clues to factors influencing HRMT. Simply described, MPS are regional pain disorders associated with a hypersensitive palpable nodule (TrP) in a taut band of skeletal muscle (Simons et al., 1999a). A snapping palpation
The 2007 International Fascia Congress and interface with HRMT
The landmark Fascia Congress (2007) illustrated that fascia is the soft tissue component of the connective tissue system that exists throughout the human body. It forms a whole-body, three-dimensional cell and extra-cellular matrix of support, continuity, and communication (Chaitow, 2006). Importantly, fascial tissues are connected to and integrated with the musculoskeletal system to provide stability and effect movements. Fascial and muscular components are united to form combined myofascial
Acknowledgments
We thank Jessica Debis for her invaluable technical assistance in completing this manuscript, Dr. Sam Betts and Profs. Jacek Cholewicki, Diane Lee, and Robert Schleip for their expert critiques of the manuscript. Support for this project was provided by the Department of Medicine, University of Illinois College of Medicine at Peoria, and a grant from the MTM Foundation.
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