In 2007, the inaugural International Fascia Research Congress was tasked with establishing a ‘functional’ definition for the fascial system. The goal was to create and clarify the term “fascial system,” promoting clear and unambiguous communication internationally, across disciplines and professions related to fascia.
This is the definition they proposed: The fascial system consists of the three-dimensional continuum of soft, collagen-containing, loose and dense fibrous connective tissues that permeate the body. It incorporates elements such as adipose tissue, adventitiae and neurovascular sheaths, aponeuroses, deep and superficial fasciae, epineurium, joint capsules, ligaments, membranes, meninges, myofascial expansions, periostea, retinacula, septa, tendons, visceral fasciae, and all.
During their examination of the subject they also came up with four categories of fascia. Each category was named based on the function of the fascia and classified according to 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 of fascia, creating a complex mix of different fascial types.
1. Linking fasciae: Predominantly dense, regular, parallel ordered, unidirectional connective tissue with a significant amount of collagen type I. Collagen Type I is a fibrous protein that is a major component of the connective tissues, including tendons, ligaments, skin, and bones. It provides strength and structure to these tissues and is known for its tensile strength. Collagen Type I is crucial for maintaining the integrity and resilience of various bodily structures, including 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 Pacinian 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.
2. 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.
3. Compression fasciae is a mixture of dense, regular multidirectional and parallel ordered connective tissue layers that wrap around 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, creating a dynamic and resilient structural network that adapts to varying mechanical stresses. The presence of loose connective tissue between adjacent layers permits effective local sliding.
This fascia also contains proprioceptors, however its role as a sensory organ is less significant than that of the linking, or fascicular categories.
4. 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, forming a mesh-like structure, and elastin fibers, providing elasticity in the tissue composition, are the main components of the extracellular matrix (ECM). Trace amounts of other collagen fibers are also present. The reticular fibers offer a supporting framework, and the elastic fibers create a three-dimensional network, enabling separating fascia to respond effectively 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 mainly to detect when tissues are stretched or compressed. Pacinian corpuscles, sensitive to deep pressure, and Ruffini’s corpuscles, which respond slowly to sustained pressure and lateral forces, are believed to be concentrated in many parts of separating fascia, such as in subcutaneous tissue. Deep sustained pressure may be necessary for manual practitioners to affect this fascial tissue.
As research continues and we learn more about fascia, and its many complex roles, we also gain insights into effective ways to maintain its health.
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