Physiology Review
Human resting muscle tone (HRMT): Narrative introduction and modern concepts

https://doi.org/10.1016/j.jbmt.2008.05.007Get rights and content

Summary

Human resting muscle (myofascial) tone (HRMT) is the passive tonus or tension of skeletal muscle that derives from its intrinsic (EMG-silent) molecular viscoelastic properties. The word tone has been used to convey varying clinical and physiological features that have led to confusion and controversy. HRMT is the vital low-level, passive tension, and resistance to stretch that contributes importantly to maintain postural stability in balanced equilibrium positions. In contrast, co-contraction of muscle is an active neuromotor control that provides greater levels of tonus for increased stabilization. Functionally, HRMT is integrated with other passive fascial and ligamentous tensional networks of the body to form a biotensegrity system. This review aims to achieve better understandings of HRMT and its functional roles.

Nature is frugal and man's adaptations to gravitational forces and erect postures seemingly evolved mechanisms in skeletal muscle tissues to economically enhance stability. Normal passive muscle tone helps to maintain relaxed standing body posture with minimally increased energy costs (circa 7% over supine), and often for prolonged durations without fatigue. Available data infer polymorphic variations in normal myofascial tone. However, few quantitative studies have been performed to establish normal frequency distributions of degrees of myofascial tone. Clinical experience indicates that persons with certain symptomatic musculoskeletal conditions may have palpably increased resting muscle firmness or hardness (EMG-silent), such as that of the upper trapezius in tension-type headache, and the lumbodorsal extensors (hartspann) in degenerative lumbar disc disease and ankylosing spondylitis.

In summary, resting skeletal muscle tone is an intrinsic viscoelastic tension exhibited within the body's kinematic chains. It functions inseparably from fascial (i.e., myofascial) tissues and ligamentous structures. Thus, HRMT is a passive myofascial property which operates within networks of tensional tissues, i.e., biotensegrity. This passive tension is the CNS-independent component resulting from intrinsic molecular interactions of the actomyosin filaments in sarcomeric units of skeletal muscle and myofibroblast cells. The overarching CNS-activated muscle contractions generate far greater tensions transmitted by fascial elements. Interdisciplinary research on HRMT and its biodynamics promises greater effectiveness of clinical practitioners and productivity of investigators, which warrants priority attention.

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.

References (118)

  • J.C. Hannon

    Connective tissue perspectives: stillness, salience and the sensibilities of stroma

    Journal of Bodywork and Movement Therapies

    (2000)
  • J.C. Hannon

    The physics of Feldenkrais. Part 4: Axes, levers, struts and strain

    Journal of Bodywork and Movement Therapies

    (2001)
  • J.C. Hannon

    The physics of Feldenkrais. Part 5: Unstable equilibrium and its application to movement therapy

    Journal of Bodywork and Movement Therapies

    (2001)
  • J.C. Hannon

    Wartenberg. Part 3: Relaxation training, centration and skeletal opposition: a conceptual model

    Journal of Bodywork and Movement Therapies

    (2006)
  • H. Johansson et al.

    Pathophysiological mechanisms involved in genesis and spread of muscular tension in occupational muscles pain and in chronic musculoskeletal pain syndromes: a hypothesis

    Medical Hypotheses

    (1991)
  • R. Lardner

    Stretching and flexibility: its importance in rehabilitation

    Journal of Bodywork and Movement Therapies

    (2001)
  • P. Latey

    Feelings, muscles and movement

    Journal of Bodywork and Movement Therapies

    (1996)
  • C. Liebenson

    The relationship of the sacroiliac joint, stabilization musculature, and lumbo-pelvic instability

    Journal of Bodywork and Movement Therapies

    (2004)
  • C. Liebenson

    Spinal stabilization—an update. Part 1—Biomechanics

    Journal of Bodywork and Movement Therapies

    (2004)
  • T.S.K. Lyttle

    The Feldenkrais Method: application, practice and principles

    Journal of Bodywork and Movement Therapies

    (1997)
  • T.W. Myers

    The ‘anatomy trains’: part 2

    Journal of Bodywork and Movement Therapies

    (1997)
  • T.W. Myers

    Kinesthetic dystonia: what bodywork can offer a new physical education

    Journal of Bodywork and Movement Therapies

    (1998)
  • T.W. Myers

    Kinesthetic dystonia: the contribution of bodywork to somatic education

    Journal of Bodywork and Movement Therapies

    (1999)
  • T.W. Myers

    Structural integration—developments in Ida Rolf's ‘Recipe’—I

    Journal of Bodywork and Movement Therapies

    (2004)
  • T.W. Myers

    Structural integration—developments in Ida Rolf's ‘recipe’—Part 3. An alternative form

    Journal of Bodywork and Movement Therapies

    (2004)
  • J.L. Oschman

    The electromagnetic environment: implications for bodywork. Part 1: Environmental energies

    Journal of Bodywork and Movement Therapies

    (2000)
  • R. Schleip

    Fascial plasticity—a new neurobiological explanation: Part 1

    Journal of Bodywork and Movement Therapies

    (2003)
  • R. Schleip

    Fascial plasticity—a new neurobiological explanation: Part 2

    Journal of Bodywork and Movement Therapies

    (2003)
  • J.P. Shah et al.

    Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points

    Archives of Physical Medicine and Rehabilitation

    (2008)
  • D.G. Simons

    New views of myofascial trigger points: etiology and diagnosis

    Archives of Physical Medicine and Rehabilitation

    (2008)
  • D.G. Simons et al.

    Understanding and measurement of muscle tone as related to clinical muscle pain

    Pain

    (1998)
  • M.M. Abitbol

    Effect of posture and locomotion on energy expenditure

    American Journal of Physical Anthropology

    (1988)
  • M. Adams et al.

    The Biomechanics of Back Pain

    (2002)
  • G. Albrecht-Buehler

    Is cytoplasm intelligent too?

    Cell and Muscle Motility

    (1985)
  • Aristotle, Metaphysics, Book H, 1045b, pp....
  • M. Ashina et al.

    Tender points are not sites of ongoing inflammation—in vivo evidence in patients with chronic tension-type headache

    Cephalalgia

    (2003)
  • S. Ashina et al.

    Pathophysiology of tension-type headache

    Current Pain and Headache Reports

    (2005)
  • J.V. Basmajian et al.

    Muscles Alive: Their Functions Revealed by Electromyography

    (1985)
  • K.S. Campbell et al.

    A cross-bridge mechanism can explain the thixotropic short-range elastic component of relaxed frog skeletal muscle

    The Journal of Physiology

    (1998)
  • J. Cholewicki et al.

    Relationship between muscle force and stiffness in the whole mammalian muscle: a simulation study

    The Journal of Biomechanical Engineering

    (1995)
  • J. Cholewicki et al.

    Stabilizing function of trunk flexor-extensor muscles around a neutral spine posture

    Spine

    (1997)
  • S. Clemmesen

    Some studies on muscle tone

    Proceedings of the Royal Society of Medicine

    (1951)
  • C. Couppé et al.

    Myofascial trigger points are very prevalent in patients with chronic tension-type headache: a double-blinded controlled study

    The Clinical Journal of Pain

    (2007)
  • R.A. Davidoff

    Skeletal muscle tone and the misunderstood stretch reflex

    Neurology

    (1992)
  • D. Denny-Brown

    On the nature of postural reflexes

    Proceedings of the Royal Society of London Series B

    (1929)
  • E.W. Donisch et al.

    Electromyography of deep back muscles in man

    The American Journal of Anatomy

    (1972)
  • M.R. Durette et al.

    Needle electromyographic evaluation of patients with myofascial or fibromyalgic pain

    American Journal of Physical Medicine and Rehabilitation

    (1991)
  • M. Feldenkrais

    Body and Mature Behaviour: A Study of Anxiety, Sex, Gravitation and Learning

    (1949)
  • M. Feldenkrais

    Awareness Through Movement

    (1972)
  • Cited by (122)

    View all citing articles on Scopus
    1

    Tel.: +1 805 542 9925; fax: +1 805 541 2391.

    View full text