Article

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

University of Illinois College of Medicine at Peoria, Peoria, IL 61656, USA.
Journal of bodywork and movement therapies 11/2008; 12(4):320-32. DOI: 10.1016/j.jbmt.2008.05.007
Source: PubMed

ABSTRACT

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.

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    • "The estimation of muscle tone is important in clinical practice, occupational health, physiotherapy, and rehabilitation medicine as well as in other health-related areas. New technical possibilities have been elaborated for the corresponding measuring devices, with good validity and simple usage (Clemmesen, 1951; Davidoff, 1992; Masi and Hannon, 2008; Gurfinkel et al., 2011). * Corresponding author, helena.gapeyeva@ut.ee "

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    • "Although an increase in intra-muscular pressure as the result of lateral tissue constraint would increase muscle stiffness and lead to increased force production during active contraction (Purslow, 2002), muscles are not like pressurized balloons (Levin, 2002; Sharkey, 2015 ) and most of the water contained within them is tightly bound to a wide diversity of proteoglycan complexes that are cross-linked with the collagen fibres (Gillies and Lieber, 2011). While the measurement of normal intra-muscular pressures during contraction (15e141 mm Hg) is notoriously difficult (Hill, 1948; Ward et al., 2007; Aweid et al., 2012), pressures of 6e12 mm Hg at rest (Aweid et al., 2012) may be at least partly due to the passive muscle stiffness, or intrinsic tension, that naturally occurs in muscle tissues invivo (Schleip et al., 2006; Masi and Hannon, 2008). Collagens are the main tension-bearing element within ECM/fascial tissues and are aligned parallel to the local tissue strain (Purslow, 2010) with the cells contained within them also contributing to this tension (Tomasek et al., 2002). "
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