Clinical, Biomechanical, and Physiological Translational Interpretations of Human Resting Myofascial Tone or Tension

Abstract

Methods: Biomechanical, clinical, and physiological studies were reviewed to interpret the passive stiffness properties of HRMT that help to stabilize various relaxed functions such as quiet balanced standing. Biomechanical analyses and experimental studies of the lumbar multifidus were reviewed to interpret its passive stiffness properties. The lumbar multifidus was illustrated as the major core stabilizing muscle of the spine, serving an important passive biomechanical role in the body.Results: Research into muscle physiology suggests that passive resting tension (CNS-independent) is generated in sarcomeres by the molecular elasticity of low-level cycling cross-bridges between the actomyosin filaments. In turn, tension is complexly transmitted to intimately enveloping fascial matrix fibrils and other molecular elements in connective tissue, which, collectively, constitute the myofascial unit. Postural myofascial tonus varies with age and sex. Also, individuals in the population are proposed to vary in a polymorphism of postural HRMT. A few people are expected to have outlier degrees of innate postural hypotonicity or hypertonicity. Such biomechanical variations likely predispose to greater risk of related musculoskeletal disorders, a situation that deserves greater attention in clinical practice and research. Axial myofascial hypertonicity was hypothesized to predispose to ankylosing spondylitis. This often-progressive deforming condition of vertebrae and sacroiliac joints is characterized by stiffness features and particular localization of bony lesions at entheseal sites. Such unique features imply concentrations and transmissions of excessive force, leading to tissue micro-injury and maladaptive repair reactions.Conclusions: The HRMT model is now expanded and translated for clinical relevance to therapists. Its passive role in helping to maintain balanced postures is supported by biomechanical principles of myofascial elasticity, tension, stress, stiffness, and tensegrity. Further research is needed to determine the molecular basis of HRMT in sarcomeres, the transmission of tension by the enveloping fascial elements, and the means by which the myofascia helps to maintain efficient passive postural balance in the body. Significant deficiencies or excesses of postural HRMT may predispose to symptomatic or pathologic musculoskeletal disorders whose mechanisms are currently unexplained.

Integrative Structural Biomechanical Concepts of Ankylosing Spondylitis

“…The target enthesis lesions in AS are generally interpreted to result from inflammatory mechanisms associated with biomechanical stress at the local level [ 14 ]. The axial myofascial hypothesis proposes a centralized mechanism for increased tensional stresses in the postural musculoskeletal anatomy that can transmit excessive forces to entheses in the spine and girdles [ 15 , 16 ]. A normally relaxed muscle is relatively soft and extensible.…”

“…To the contrary, stiffer muscles less effectively absorb or distribute forces [ 13 ]. Thus, stiffer and tenser muscles could likely transmit greater stresses to tendons or ligaments and to bony enthesis sites, which serve an anchoring role [ 13 , 15 ].…”

“…Anatomical cross-bracing of the dorsal and lateral postural myofascial support systems could overload the SIJs by increased compressional forces and stiffness ( Figure 1 ) [ 16 ]. Hypertonicity of the deeper vertebral myofascial system, like the lumbar multifidus muscles, could exert its main effects on increased tensional forces at the spinal entheses and manifest as symptomatic and objective postural stiffness [ 15 ].…”

“…Axial or postural human resting muscle/myofascial tone (HRMT) is an innate polymorphic trait which is independent of the central nervous system control and contributes vitally to stability in balanced equilibrium positions [ 15 , 20 , 21 ]. Increased low-back muscle stiffness and tightness in patients with early AS was first reported by Forestier et al in 1951 [ 22 ], which was called the “bowstring sign” [ 22 ].…”

“…The concept of HRMT is believed to incorporate an innate individual variability (polymorphism), particularly of the axial postural system [ 15 , 24 ]. Variability is also likely to be clinically relevant to proximal limb muscles and girdles, but less so for the distal extremities.…”