Significance of epimuscular myofascial force transmission under passive muscle conditions

Abstract

In the past 20 yr, force transmission via connective tissue linkages at the muscle belly surface, called epimuscular myofascial force transmission, has been studied extensively. In this article, the effects of epimuscular linkages under passive muscle conditions are reviewed. Several animal studies that included direct (invasive) measurements of force transmission have shown that different connective tissue structures serve as an epimuscular pathway and that these tissues have sufficient stiffness, especially at supraphysiological muscle lengths and relative positions, to transmit substantial passive forces (up to 15% of active optimal force). Exact values of lumped tissue stiffness for different connective tissue structures have not yet been estimated. Experiments using various imaging techniques (ultrasound, MRI, shear wave elastography) have yielded some, but weak, evidence of epimuscular myofascial force transmission for passive muscles in humans. At this point, the functional consequences of epimuscular pathways for muscle and joint mechanics in the intact body are still unknown. Potentially, however, these pathways may affect sensory feedback and, thereby, neuromuscular control. In addition, altered epimuscular force transmission in pathological conditions may also contribute to changes in passive range of joint motion.

The Structure and Role of Intramuscular Connective Tissue in Muscle Function

“…This idea has since been supported by computational models (see below) and argues that shear stains in the perimysium must be larger than shear strains though the endomysium between muscle fibers in a fascicle. This is in contrast to the interpretation of those researchers (e.g., Huijing, 2009;Maas, 2019) who stress the importance of lateral force transmission between fascicles and between entire muscles (epifascial force transmission) as an important physiological function, as a perimysium easily deformed in shear would not be an efficient means to transmit contractile force laterally between fascicles.…”

“…A general recognition that force transmission can readily occur between adjacent muscle fibers has been followed by evidence that myofascial force transmission can occur between fascicles even between adjacent muscles, as summarized by Huijing (2009); Maas and Sandercock (2010), and Maas (2019). While there is some dispute that epimysial force transfer between individual muscles is significant (Diong et al, 2019), the general idea of lateral force transmission between adjacent fibers within a muscle fascicle is less controversial.…”

Principles of the Mechanism for Epimuscular Myofascial Loads Leading to Non-uniform Strain Distributions Along Muscle Fiber Direction: Finite Element Modeling

“…However, finite element modeling allows addressing mechanical principles of that, and the present findings show the role of epimuscular myofascial loads on along muscle fiber strain distributions. It was pointed out recently (Maas, 2019) that such modeling may be used to elaborate on the findings of Pamuk et al (2016). The present study accomplishes that by three model cases, which exemplify scenarios that yield uniform direction of strains if EMFT mechanism is ignored, and strains of opposite directions and heterogeneous amplitudes occurring along the same fascicles if it is not.…”

Investigating Passive Muscle Mechanics With Biaxial Stretch

“…Other efforts to characterize the anisotropy of passive muscle have employed uniaxial stretch in both the longitudinal and transverse (cross-fiber) directions (Morrow et al, 2010;Takaza et al, 2012;Mohammadkhah et al, 2016;Wheatley et al, 2016b). However, during contraction and passive stretch, force is transmitted laterally both within skeletal muscle and between muscles (Huijing, 1999;Ramaswamy et al, 2011;Maas, 2019;Csapo et al, 2020), suggesting that muscle tissue is subject to a multi-axial stress state in vivo. This is further supported by the structure of the ECM, which consists of collagen fibrils that are dispersed around the transverse plane (Purslow, 1989;Purslow and Trotter, 1994;Gillies and Lieber, 2011).…”