Fascia is almost inseparable from all structures in the body. A fibrous network of connective tissues, it surrounds all muscles, bones, ligaments, tendons and organs, holding different parts in place, suspending organs, nerves and blood vessels and allowing parts of the body to slide smoothly across each other.
Fascia has no beginning or end. It’s key characteristic, continuity, helps explain concepts such as myofascial force transmission.
The First International Fascia Research Congress (2007) defined fascia as an innervated, continuous, functional organ of stability and motion that is formed by 3-dimensional collagen matrices and include joint and organ capsules, muscular septa, ligaments, retinacula, aponeuroses, tendons, myofascia, neurofascia and other fibrous collagenous tissues as forms of fascia, inseparable from surrounding connective tissues.
There are 4 categories of fascia, named after the function of the fascia (linking, fascicular, compression, and separating fasciae) and based on collagen type ratio, extracellular matrix proteins, nerve fiber types, myofascial force transmitting potential, fiber orientation, and influence on the circulatory system. Each region of the body contains multiple categories, creating a complex mix of different fascial types.
Linking fasciae is predominantly dense, regular, parallel ordered, unidirectional connective tissue with a significant amount of collagen type I. This includes fascia of muscles, fascia of regions (head & neck, trunk, limbs), aponeuroses, tendinous arches and neurovascular sheaths.
This category is subdivided into dynamic and passive divisions. The dynamic division includes major fascial groups more significantly related to movement and joint stability and contains higher concentrations of contractile and proprioceptive fibers. The innervation of dynamic linking fascia differentiates it from other categories, by contributing to nociception and proprioception. It is also densely innervated by free nerve endings and Paciniform corpuscles which respond to rapid pressure and vibration.
The passive division is acted on by other extramuscular tissues to maintain continuity throughout the body or form tunnels and sheaths. This group can act as muscular insertion points and joint linkages and ultimately provide proprioceptive information when tension is exerted. The passive linking fasciae can only transmit force when they are stretched and loaded, while dynamic fasciae can theoretically contract more autonomously like smooth muscle, thereby affecting tension in the musculoskeletal system.
Fascicular fasciae forms adaptable tunnels which bundle vessels and fascicles within muscle, tendon, bone and nerves. Fascicular fasciae plays a role in organization, transport, strength and locomotion. This category is a mixture of both loose and dense multidirectional connective tissues that form an extensive system of tunnels that connects and dissipates force within muscle and provides intramuscular pathways and support for nerves, blood vessels and lymphatics. The fascicular fasciae of the muscle converges into a dense connective tissue link at the myotendinous junction to become fascicular fascia of the tendon. At this junction, fascicular fasciae is richly innervated by Golgi tendon organs which are stimulated by muscle contraction. Fascicular fasciae allow forces to be transferred from within muscle to synergistic muscles, and through the linking fascia, to antagonistic muscles.
Compression fasciae is a mixture of dense, regular multidirectional and parallel ordered connective tissue layers that ensheath whole limbs to create a stocking effect. This fascial category plays an important role in locomotion and venous return due to its influence on compartmental pressure, muscle contraction and force distribution. For example, the crural (relating to the leg) fascia is composed of two or three layers of parallel ordered collagenous fiber bundles, each layer being separated by a thin layer of loose connective tissue. The orientation of the collagen fibers changes from layer to layer within the compression fascia. The presence of loose connective tissue between adjacent layers permits effective local sliding.
There are proprioceptors embedded in this fascia, however its role as a sensory organ is less significant than that of the linking, or fascicular categories.
Separating fascia is generally loose connective tissue and dense irregular connective tissue. This group of fascia has a unique appearance and texture, ranging from transparent woven sheets to a fuzzy cotton-like consistency. Reticular collagen fibers and elastic fibers are the major components of the ECM, with small amounts of other collagen fibers. While the reticular fibers provide a supporting framework, the elastic fibers form a three dimensional network to allow separating fascia to respond to stretch and distention. Separating fascia divides the body in visible sheets and layers allowing it to take up forces and friction in all directions. While its major function is to allow more efficient sliding of tissues over one another, it may still form adhesions from faulty movement patterns or injury.
Separating fascia’s innervation serves primarily to sense distension and compression of tissues. Concentrations of Pacinian corpuscles (detecting deep pressure) and Ruffini’s corpuscles, which responding slowly to sustained pressure and tangential forces, are thought to be present in much of separating fascia, for example, in subcutaneous tissue. Deep sustained pressure may be necessary for manual practitioners to affect this fascial tissue.
Fascial restrictions can form in any type of fascia, through chronic stress, overuse, inflammation, inactivity or injury. When stuck, it squeezes the structures it surrounds, inhibiting movement and creating pressure, malnourishment and pain. Fascial restrictions can be so firm that they limit movement, distort muscle function, cause nerve issues, behavioral problems, myfascial pain and soft tissue injuries.
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