Introduction

Researchers disagree on a single comprehensive definition of "fascia." Despite scientific uncertainty, medical texts agree that fascia covers every structure of the body, creating structural continuity that confers form and function to all tissues and organs. Fascial tissue exhibits ubiquitous distribution throughout the body. This tissue can wrap, interpenetrate, support, and constitute blood vessels, bone tissue, meningeal tissue, organs, and skeletal muscles. Fascia forms interdependent layers from the skin to the periosteum, creating a 3-dimensional mechano-metabolic structure.[1][2][3]

Several major scholarly groups have proposed definitions of fascia. The Federative Committee on Anatomical Terminology (FCAT, 1989) distinguished between the superficial fascia—a loose subcutaneous tissue layer—and the deep fascia located underneath. The Federative International Programme on Anatomical Terminologies (FIPAT, 2011) described fascia as any dissectible connective tissue beneath the skin that attaches, encloses, and separates muscles and organs. This definition emphasized fascia as connective tissue that divides, supports, and structures bodily components, excluding only the epidermis. 

In 2014, the Fascia Nomenclature Committee, part of the Fascia Research Society, proposed the broader concept of a fascial system as a continuous 3-dimensional network of connective tissues, including fasciae, tendons, ligaments, membranes, and additional structures, that integrates all body systems. In 2013, the FORCE (Foundation of Osteopathic Research and Clinical Endorsement) group similarly expanded on this concept, describing fascia as a dynamic continuum linking tissues, fluids, and organs that transmits mechanical and metabolic information throughout the body (see Image. Structural Elements Identified as Connective Tissue). Collectively, these definitions portray fascia as an uninterrupted connective network derived from mesodermal tissues, essential for maintaining structural and functional unity.[4][5][6]

Structure and Function

Mechanical Function

Normal movement of the body is facilitated by fascial tissues and their inseparable interconnections, which allow sliding of muscular structures, sliding of nerves and vessels between contractile fields and joints, and coordinated mobility of all organs according to body position. A fundamental characteristic of fascia is its ability to adapt to mechanical stress, remodeling cellular and tissue structures to reflect the functional demands of the surrounding environment. For example, the plantar fascia in the foot employs a mechanical model known as the "windlass mechanism" to provide dynamic support for the medial longitudinal arch while the limb transitions from the heel-strike to the toe-off phases of the gait cycle (see Image. Plantar Aponeurosis).[7]

The fascial continuum enables proper distribution of tension information generated by tissues covered or supported by fascia. This mechanism allows the entire body system, including the epidermis, to interact in real time.

Emotional Function

Fascial unity influences not only movement but also emotional states. Dysfunction of the fascial system, perpetuated by habitual movements, can induce emotional alterations. These alterations may originate from constant myofascial nonphysiological afferents, aligning the emotional state with the myofascial pathology. Body position stimulates emotional centers, and the presence of myofascial alterations produces postural changes.[8]

The myofascial system exhibits extensive, fine, and diversified innervation. Myelinated proprioceptive terminations (Ruffini, Golgi, and Pacini) are located inside or near connective tissue in close association with muscles, while numerous fine unmyelinated free nerve endings contact the periosteum, connective tissue layers such as endomysium and perimysium, and the connective tissue of all viscera. These receptors mediate proprioception, nociception, and interoception. Afferent pathways of interoception project to autonomic and medullary centers and the brainstem, where sorting occurs in the anterior cingulate cortex and posterior dorsal insula via thalamocortical extensions. Interoception modulates exteroceptive body representation and pain tolerance. Dysregulation of interoceptive pathways can distort body image and influence emotional states.

Fascia maintains a close relationship with the nervous system, influencing both proprioception and emotional regulation. Fascial tissue demonstrates increased tightness and reduced elasticity in patients with chronic depression, whether due to illness or pain.[9]

Embryology

Many tissues are derived from connective tissue, including blood, bone, cartilage, lymphoid and hematopoietic tissue, adipose tissue, tendons, ligaments, perimysium, epimysium, endomysium, meningeal tissue, and all visceral communication and coverage fasciae, originating from mesenchyme. During embryonic development, connective tissue directs the morphogenesis of the structures it will contain and connect.

Embryonic mesenchyme, also termed "connective embryonic mesenchyme" or "undifferentiated mesenchyme," consists of star-shaped cells with high mitotic activity. These cells are considered pluripotent, capable of differentiating into multiple tissue types. Embryonic mesenchyme serves as the source of numerous connective structures and stromal stem cells. During development, mesenchymal cells occupy spaces between embryonic layers, connect diverse structures, and constitute organ stroma.

Mesenchyme is present in and derived from all 3 embryonic layers—ectoderm, mesoderm, and endoderm—particularly from mesoderm and ectoderm. Current data and animal models indicate that all structures encompassed by the fascia definition in the head (eg, muscles, bones, and skin) and cervical region originate from mesoderm and ectoderm.[10]

Blood Supply and Lymphatics

Blood and lymph originate from mesoderm and are classified as connective tissues. In addition to nutritive functions, blood functions as a conduit linking organs, which communicate through hormones and chemical mediators, ensuring integration of organismal functions. Immune cells and platelets are transported to sites requiring their activity, including areas of inflammation, sites containing antibodies and clotting system proteins, and locations reached by numerous transport proteins such as lipoproteins, transferrin, ceruloplasmin, and albumin, which bind water-insoluble circulating compounds.

Blood is connective tissue composed of cells and cell fragments suspended in an extracellular matrix of complex composition. A distinctive feature of blood is its liquid extracellular matrix, classifying it as a fluid connective tissue. Centrifugation separates blood into 2 components. The 1st component is a fluid matrix termed "plasma." The 2nd component consists of corpuscles, which are cells or cell fragments.

Corpuscles comprise erythrocytes, platelets, and leukocytes. Only leukocytes are complete cells. Erythrocytes are anucleate, and platelets are cell fragments. Erythrocytes are present in greater quantities than other elements, which accounts for their predominant influence on hematocrit values compared with leukocytes or platelets, which constitute approximately 1% of total blood volume. Erythrocytes, like other blood elements, are generated by pluripotent stem cells located in the bone marrow, particularly in the ribs, sternum, pelvis, and vertebrae.

Leukocytes are divided into distinct types. Granulocytes contain large cytoplasmic granules that are visible under an optical microscope after staining. Granulocytes are classified as neutrophils, which exhibit affinity for neutral dyes; eosinophils, which stain with acidic dyes; and basophils, which stain with basic dyes. Lymphocytes, including T and B lymphocytes and natural killer cells, participate in specific immune defense by recognizing, targeting, and attacking pathogens. This targeted response almost always involves the production of circulating proteins called "antibodies." Monocytes are the largest leukocytes and are characterized by a large, horseshoe-shaped nucleus.

The Lymphatic System

The lymphatic system efficiently removes excess interstitial fluid, solutes, and various cells, directing them into the bloodstream and maintaining the balance between plasma and interstitial fluid volumes. The system originates from interstitial structures known as initial lymphatics, which are small capillaries bounded by discontinuous endothelium and basement membrane, providing low resistance to the flow of fluids and substances, including hydrophilic molecules, cells, viruses, and bacteria. Initial lymphatics attach to the cell surface via collagen fibrils (type VII collagen). This collagen facilitates transmission of mechanical forces toward the lumen of the lymphatic vessel. Some lymphatic vessels exhibit autonomous contraction driven by filaments analogous to actin.

Initial lymphatics enlarge to form collecting ducts composed of collagen, smooth muscle cells, and elastic fibers. Recent data indicate that lymphatic vessels possess intrinsic tone and probable autonomous contractile activity, with high sensitivity to flow variations, reflecting sensory functions. Lymphatic vessels are surrounded by autonomic nerves, predominantly sympathetic fibers, which may coordinate lymphatic transport. These vessels adapt and modify their elastic properties, enhancing or impairing lymphatic transport function.

Primary valves are formed by cytoplasmic extensions of adjacent endothelial cells linked by tight junctions. The valves protrude into the lumen, preventing retrograde flow. Intraluminal valves, which are weaker, consist of 2 sheets attached to opposite sides of the lymphatic vessel and connected to zonules, peripheral junctions formed by a band encircling the cell. Lymph flow is driven by external mechanical compressions, such as those generated by muscle contraction, and by intrinsic contractile activity of the vessels.

The lymphatic system undergoes aging, resulting in reduced elasticity, formation of aneurysms, and decreased numbers of blood vessels or lymphangions, the functional units of the lymphatic system. Recent evidence demonstrates that lymphatic vessels are innervated by vagal cholinergic and sympathetic fibers capable of modulating peristaltic contractions in vessels containing contractile fibers with actin-like proteins. These thin nerves penetrate from the external layer of the lymphatic vessel to the deepest endothelial layer. The neural network deteriorates with age. Parasympathetic and sympathetic innervation likely functions both as modulators of vessel tone and sensors of the contractile layer.

The Dural System

The dural system contains a lymphatic network known as the glymphatic system. Cerebrospinal fluid (CSF) is drained through both venous and lymphatic pathways.

Dural lymphatic vessels run adjacent to cerebral veins and arteries. These vessels exit the skull, following the reverse course of the pterygopalatine artery and a branch of the internal carotid artery, and traverse external venous routes as well as cranial nerves emerging from the skull.

Lymphatic vessels follow venous pathways across the cribriform plate toward the nasal mucosa, providing routes for CSF egress. The lymphatic system absorbs interstitial fluid and CSF from the subarachnoid space and transports it out of the skull, primarily from the base to the cervical spine. This drainage mechanism is most active during sleep.

Nerves

The innervation influencing the fascial system is autonomic, comprising sympathetic and parasympathetic components. The fascial system constitutes the connective tissue layers of the nerve, including the epineurium, perineurium, and endoneurium. All layers receive innervation and contain a thin but potentially significant plexus of nociceptors. The sliding of fascial structures surrounding the nerve, as well as the gliding of the nerve among the tissues it traverses and innervates, is essential for maintaining nerve health.

Muscles

Influence of Connective Tissue Organization on Muscle Form

Fascial structures largely determine the capacity to transmit generated force (see Image. Fascial Layers). This capacity not only enables the transport of mechanical tension but also allows the storage of mechanical energy, conserving myoelectric energy. The connective tissue forming the various muscular layers is predominantly derived from fibroblasts.

Muscles contribute to the regulation of mechanical tension by rapidly altering the morphology of their cytoskeleton, a process facilitated by fibroblasts. Transient morphological changes occur in the myofascial system in response to brief mechanical stimulation of its connective and contractile components. Persistent mechanical forces induce chronic modifications in the form and function of the myofascial system.

Individual fibroblasts can sense the functional state of both neighboring and distant cells, ensuring fascial and mechanical continuity. Additional cell types are present within connective tissue, many of which have not yet been fully characterized or cataloged.

Superficial and deep fascia covering and compartmentalizing muscles contain specialized fibroblasts referred to as "fasciacytes." These cells are responsible for the production of hyaluronic acid, a high-molecular-weight glycosaminoglycan polymer of the extracellular matrix. Hyaluronic acid dampens mechanical tension, occupies intercellular spaces, and facilitates sliding between tissue layers. Fasciacytes are predominantly located in regions with dense innervation, including nerve endings, Pacini corpuscles, and Ruffini corpuscles.

Another cell type present within connective tissue is the telocyte. Limited studies have examined these cells in fascial structures, particularly in the fascia lata, thoracolumbar fascia, crural fascia, and plantar fascia. Telocytes are widely distributed across human tissues and participate in diverse biological processes. These cells form networks within the fascia, establishing homocellular junctions with other telocytes and heterocellular junctions with other cell types, including fibroblasts, endothelial cells, stem cells, and adipocytes. These interactions allow telocytes to influence the metabolic environment and contribute to tissue repair and remodeling. Telocytes likely affect hyaluronic acid production. However, the precise role of these cells within fascial tissue remains unknown.[11]

Surgical Considerations

Surgical adhesions arise from impaired sliding between fascial layers. The resulting restriction of movement generates an inflammatory environment that promotes adhesion formation. Adhesions subsequently develop their own vascularization and innervation, establishing autonomous tissue distinct from surrounding structures. These adhesions can contribute to recurrent pain in numerous postsurgical syndromes.

Clinical Significance

The muscular system constitutes an integral component of the fascial continuum. Muscular function undergoes nonphysiological alterations in the context of systemic diseases and disorders, whether visceral, genetic, vascular, metabolic, or alimentary in origin. Epigenetic processes induce adaptation in the absence of mechanotransduction, further compromising muscular properties.[12]

Chronic Fatigue

Chronic fatigue may be associated with the fascial system, particularly when pathological disorders persist over several years. Fibrosis of fascia or impaired sliding between tissue layers restricts bodily movements. Restricted and uncoordinated movements produce elevated levels of anaerobic metabolites, which are interpreted by the central nervous system as fatigue. Fibromyalgia exemplifies this mechanism.

Pain

Elevated levels of circulating cytokines derived from the connective tissue system in systemic diseases may contribute to neuropathic pain. Connective tissue can directly transmit nociceptive signals, as it contains receptors capable of converting mechanical stimuli into pain. Nonphysiological mechanical stimuli may transform proprioceptors into nociceptors. Nociceptors synthesize neuropeptides that modify the surrounding tissue and create an inflammatory environment. The epineurium and perineurium, components of the fascial system, are innervated by nervi nervorum. Exposure to pro-inflammatory molecules in these structures can generate pain sensations and establish a self-perpetuating cycle of nociception.

All fascial layers require hyaluronic acid to slide over one another. Decreased quantity or nonhomogeneous distribution compromises the ability of local or systemic sliding of connective tissue. Substantial evidence indicates that changes in the viscoelasticity of the fascial system are an important cause of nociceptor activation. Hyaluronic acid may become adhesive and less lubricating, altering the lines of force within different fascial layers. This mechanism could contribute to joint stiffness and morning pain.

Altered adjustable tension may arise from the contractile capacity of fibroblasts, generating fascial tone independent of neurological input. This contractile activity can create an inflammatory environment with fibroblast hyperplasia, leading to chronic inflammation and nociceptor sensitization. Inflammation mediated by fibroblasts increases extracellular edema, which depends not solely on vascular permeability but also on the loose fascial tissue that retains fluids. The edema elevates tension and rigidity, impeding the sliding of fascial layers and producing pain. This framework stimulates fibroblasts to release adenosine triphosphate (ATP), thereby activating nociceptors.

Nociceptor sensitization may result from local ischemia induced by nonphysiological fascial tension. This ischemia impairs skeletal muscle function and can generate trigger points.[13][14]

Immune Response

Fibroblasts influence the immune system and, consequently, bone tissue—a relationship described as osteoimmunology. The immune system and bone tissue share molecular interactions, including transcription factors, signaling molecules, and membrane receptors. Osteoclasts and cytokines reciprocally sensitize one another. Impaired flow of the fascial continuum, with its layers stacked from the most superficial fascia to the periosteum, generates an inflammatory environment, either acute or chronic. Cytokines produced under these conditions may stimulate osteoclast activation and bone resorption, which can contribute to the development of osteoporosis over time.

Fibrosis or fibromatosis arises from disorganization of connective tissue, accompanied by hyperplasia and hypertrophy of fibroblasts due to chronic inflammation, nonphysiological mechanical stress, or immobility. This condition is a recognized phenomenon associated with calcification. When fibromatosis resembles scar tissue, as observed in Dupuytren pathology, the proportion of fibroblasts differentiating into myofibroblasts increases, altering the tension sensed by the fascial continuum. This process establishes a vicious cycle of inflammation and nociceptor activation, since connective tissue is significantly more sensitive to nociceptive stimulation than muscle tissue.

Numerous chronic conditions, including heart failure, chronic obstructive pulmonary disease, fibromyalgia, and diabetes, exhibit alterations in the fascial system. These changes exacerbate the symptomatic burden experienced by affected individuals.

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References

1.

Bordoni B, Marelli F, Morabito B, Sacconi B. The indeterminable resilience of the fascial system. J Integr Med. 2017 Sep;15(5):337-343. [PubMed: 28844209]

2.

Wilke J, Schleip R, Yucesoy CA, Banzer W. Not merely a protective packing organ? A review of fascia and its force transmission capacity. J Appl Physiol (1985). 2018 Jan 01;124(1):234-244. [PubMed: 29122963]

3.

Adstrum S, Hedley G, Schleip R, Stecco C, Yucesoy CA. Defining the fascial system. J Bodyw Mov Ther. 2017 Jan;21(1):173-177. [PubMed: 28167173]

4.

Bordoni B, Simonelli M, Morabito B. The Other Side of the Fascia: Visceral Fascia, Part 2. Cureus. 2019 May 10;11(5):e4632. [PMC free article: PMC6623997] [PubMed: 31312558]

5.

Bordoni B, Escher AR, Tobbi F, Ducoux B, Paoletti S. Fascial Nomenclature: Update 2021, Part 2. Cureus. 2021 Feb 11;13(2):e13279. [PMC free article: PMC7880823] [PubMed: 33604227]

6.

Bordoni B, Escher AR. Fascial Manual Medicine: The Concept of Fascial Continuum. Cureus. 2025 Apr;17(4):e82136. [PMC free article: PMC11992952] [PubMed: 40226146]

7.

Bourne M, Talkad A, Varacallo MA. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Aug 14, 2023. Anatomy, Bony Pelvis and Lower Limb, Foot Fascia. [PubMed: 30252299]

8.

Bordoni B, Marelli F. [Emotions in Motion: Myofascial Interoception]. Complement Med Res. 2017;24(2):110-113. [PubMed: 28278494]

9.

Overmann L, Schleip R, Michalak J. Exploring fascial properties in patients with depression and chronic neck pain: An observational study. Acta Psychol (Amst). 2024 Apr;244:104214. [PubMed: 38461580]

10.

Bordoni B, Morabito B. Reflections on the Development of Fascial Tissue: Starting from Embryology. Adv Med Educ Pract. 2020;11:37-39. [PMC free article: PMC6970272] [PubMed: 32021541]

11.

Schleip R, Wilke J, Schreiner S, Wetterslev M, Klingler W. Needle biopsy-derived myofascial tissue samples are sufficient for quantification of myofibroblast density. Clin Anat. 2018 Apr;31(3):368-372. [PubMed: 29314236]

12.

Bordoni B, Marelli F, Morabito B, Sacconi B. Emission of Biophotons and Adjustable Sounds by the Fascial System: Review and Reflections for Manual Therapy. J Evid Based Integr Med. 2018 Jan-Dec;23:2515690X17750750. [PMC free article: PMC5871034] [PubMed: 29405763]

13.

Bordoni B, Marelli F, Morabito B, Sacconi B, Severino P. Post-sternotomy pain syndrome following cardiac surgery: case report. J Pain Res. 2017;10:1163-1169. [PMC free article: PMC5439996] [PubMed: 28553137]

14.

Wilke J, Schleip R, Klingler W, Stecco C. The Lumbodorsal Fascia as a Potential Source of Low Back Pain: A Narrative Review. Biomed Res Int. 2017;2017:5349620. [PMC free article: PMC5444000] [PubMed: 28584816]

Disclosure: Bruno Bordoni declares no relevant financial relationships with ineligible companies.

Disclosure: Navid Mahabadi declares no relevant financial relationships with ineligible companies.

Disclosure: Felix Jozsa declares no relevant financial relationships with ineligible companies.