Fascia

What it is

Fascia terms are unusually inconsistent. Some experts count only dense, sheet-like connective tissue (a family of tissues packed with collagen) as fascia¹. Others add very soft layers, such as the loose tissue under the skin¹. A committee of 21 experts could not agree on one meaning and produced two definitions instead¹.

Two definitions, and the debate around them

The committee’s anatomical definition calls a fascia a sheath, sheet or other collection of connective tissue under the skin that can be dissected out¹. Such tissue attaches, encloses and separates muscles and other internal organs¹. The broader term, “the fascial system”, covers a body-wide continuum of soft, collagen-containing tissues¹. It takes in tendons, ligaments, joint capsules, aponeuroses (broad, flat sheets of tendon) and the connective tissue inside and between muscles¹.

A 2026 paper by a group of anatomists argues for the traditional view⁴. In it, fasciae are fibrous membranes, mainly of dense irregular connective tissue, that divide and link body parts and are not parts of organs⁴. This view leaves out tendons and ligaments, because they are usually cord-like bundles rather than membranes⁴. The same anatomists say the fascial system takes in parts of several recognised systems, so it fails the test for an anatomical system⁴. A 2026 narrative review (a summary written without a set search method) also argues fascia should not be called an anatomical system⁵.

Fascia researchers proposed in 2025 that fasciae do form an anatomical system, with superficial, deep, visceral and neural parts⁶. In their proposal, each part has two kinds of layer: a fairly stiff, collagen-rich one and a viscous one rich in hyaluronan (a slippery, water-holding substance found between tissue layers)⁶.

Layers from the skin inward

An anatomical review describes the layers in order⁷. The superficial fascia splits the fat under the skin, the deep fascia wraps the muscles, and the epimysium (a whole muscle’s sheath) lies beneath⁷. Anatomists note that “superficial” and “deep” fascia are vague, debated terms⁴.

A 2025 review describes the superficial fascia as a thin sheet with many elastic fibres that lets the skin move separately from the muscles and deep fascia⁸. Deep fascia is often split into two kinds⁹:

• Aponeurotic fascia: a thicker, pearly-white sheet with two to three layers of parallel collagen bundles, which peels easily off the muscle below⁹.
• Epimysial fascia: a thinner sheath bound tightly to its muscle⁹.

In three fresh cadavers, deep thigh fascia was thickest on the outer side, where the iliotibial band reinforces it¹⁰.

What it is made of

A literature review lists fascia’s cells as fibroblasts (cells that make collagen), myofibroblasts (similar cells that can contract), fat cells and roaming white blood cells¹¹. Hyaluronan lies between deep fascia and muscle and helps layers glide¹². One study found a cell type that makes it, which the authors named fasciacytes¹². A systematic review (a study that sums up the research on a question in a checkable way) of 23 tissue studies, ten in humans, looked at fascia’s nerve supply¹³. It found fascia well supplied with nerve endings, mostly proprioceptors (nerve endings that sense position and movement) and nociceptors (nerve endings that sense possible harm to tissue)¹³.

How it responds to load

Most of what is known about connective tissue and exercise comes from tendons; much less is known about other fascial tissues². The tendon page covers that tendon evidence. A literature review describes fascial fibroblasts as remodelling (replacing old tissue with new) in response to the direction of mechanical pulls¹¹. The type of collagen they make changes when stress rises or when the tissue is kept still¹¹.

What sets its stiffness

A sports-medicine consensus statement lists fluid content, collagen cross-links, the surrounding material and myofibroblast contraction as things that change fascia’s mechanics². In a laboratory study, fascia samples contracted when stimulated, and the response was larger where there were more myofibroblasts¹⁴. The authors of another study offer a hypothesis: without loading, the hyaluronan between layers becomes more viscous (stickier) and slows gliding¹⁵. Loading, they suggest, makes it more fluid¹⁵.

In a randomised cross-over trial of 40 recreationally active adults, five minutes of static calf stretching lowered the stiffness of both muscle and deep fascia¹⁶. Dynamic stretching did not, against a control condition, measured straight afterwards¹⁶. Stretching has its own page.

Force passing along fascia

The consensus statement says animal and imaging studies show force can pass through fascia, not just through tendons². How much passes in living people is disputed². In living people, electrically stimulating the gastrocnemius moves the soleus beside it at the same moment².

A systematic review of 62 cadaver studies found three of six proposed muscle chains strongly supported, and no evidence for one, the “superficial front line”³. Its authors suggested that most skeletal muscles are directly linked by connective tissue³. Anatomists have found the fascial links; whether they matter for movement is the open question³. Studies measuring force along those chains are few and mixed:

Anatomists have found the fascial links; whether they matter for movement is the open question.

• Few studies: a systematic review found only nine, along three chains, and their differing methods limit comparison¹⁷.
• Uneven links: transfer was large from the plantar fascia (a band along the sole) to the Achilles tendon, marginal between a thigh muscle and a belly muscle, even though they are joined¹⁷.
• Cadaver caution: the review warns that preserved or frozen cadaver tissue behaves differently, so how far the cadaver findings apply in life is unclear¹⁷.
• Living people: in a review of 20 varied, lower-quality studies, most suggested force transfer and two suggested it was less likely¹⁸.

A 2026 meta-analysis (a study that pools earlier studies) of 15 trials found stretching or contracting a muscle raised stiffness in tissue some distance away¹⁹. The effect was moderate for stretching (very low certainty) and large for contraction (moderate certainty), with results that varied widely¹⁹. Another meta-analysis, of eight low-quality trials, found only a small, non-significant trend towards more range of motion far along one proposed chain²⁰. The consensus statement notes such distant changes may come at least partly from the nervous system, not only from mechanical links².

How it gets injured

A sports-medicine consensus statement says fascial injuries bring a significant drop in performance, in both recreational and elite sport². It adds that they could play a part in disorders such as low back pain².

From repair to scarring

Too much loading, long loading or a direct blow sets off repair in fascial tissue². If loading is long or repeated, lasting inflammation may follow². Some signalling molecules can then promote fibrosis, a build-up of excess fibroblasts and collagen². Fibrosis around tendons, nerves and muscle tissue can make structures stick together, tethering or squeezing them². A systematic review reports more nerve supply, with more nociceptors, in diseased fascia¹³.

Where muscle meets fascia

The British Athletics system grades muscle injuries on MRI (a detailed soft-tissue scan) and labels where each lies²¹:

• a: at the fascia (myofascial)²¹.
• b: where muscle joins tendon²¹.
• c: inside the tendon²¹.

A systematic review of 11 cohort studies of athletes’ muscle tears found no significant difference in return to play between “a” and “b” injuries²². The “c” injuries took longer²².

Fascia and pain

A review of systematic reviews notes that plantar fasciitis (heel pain linked to the plantar fascia) is considered degenerative rather than mainly inflammatory²³. It says the condition affects up to 17.4% of runners²³. A 2026 systematic review of 14 studies looked at the thoracolumbar fascia (a sheet over the lower and middle back) in low back pain²⁴. It found differences in thickness and stiffness between some people with and without low back pain, but not in a consistent direction²⁴. The use of these measures in practice is not established²⁴.

How training builds it

Most research on connective tissue and exercise comes from tendons; much less is known about other fascial tissues². A review of tendons, ligaments, bone and muscle describes regular training as speeding up collagen turnover and giving some net collagen gain²⁵. In fascial tissues such as tendons, the exercise-driven rise in collagen building was lower in women than in men².

A cross-sectional study (one that looks at a group once) compared 38 young elite runners without symptoms with 18 inactive people²⁶. It found no difference in plantar fascia thickness or stiffness, though it had little power to detect small differences²⁶. In a study of young and older women, the authors argued that fascia may thicken to match the forces on it¹⁵. That was an interpretation, not something the study tested¹⁵.

Popular claims research does not support

Massage, osteopathy and Rolfing are widely used for fascia, but whether they work has not been confirmed². A systematic review of eight randomised trials looked at myofascial release (hands-on pressure on muscles and their fascia) in long-term pain²⁸. It found no clinically important effects in the low back pain or fibromyalgia trials, and judged the evidence too weak to support its use²⁸. Judging fascia stiffness by touch is common, but its reliability is limited².

A 2019 review on the foam rolling page found too little evidence that releasing fascia restrictions is the main way rolling works²⁹.

Across the lifespan

The first reference study of children measured 21 healthy children aged 3 to 9³⁰. Their fascia lata was about 0.8 to 1.3 mm thick, and thickness did not correlate with age³⁰.

A cross-sectional ultrasound (sound-wave scan) study compared 18 women aged about 22 with 17 aged about 69¹⁵. The young women had thicker deep fascia in the lower leg, front of the thigh and belly wall¹⁵. The older women had thicker fascia in the lower back¹⁵. Thickness was linked with flexibility, but some links were positive and some negative¹⁵.

The consensus statement describes ageing fascia as its loose tissue growing denser and its collagen bundles scarring². It suggests this may add to age-related losses of strength or range of motion that loss of muscle alone does not explain².

Connections

The library has an entry on one named fascia, the iliotibial band, a thickening of the fascia lata on the outer thigh³¹. A 2022 review on the iliotibial band syndrome page argues stretching now and then is unlikely to change the band³².

The thoracolumbar fascia encloses the back muscles covered on the erector spinae page³³. It has been proposed that the latissimus dorsi and the opposite gluteus maximus can both tension this fascia³³.

Related stretch pages: the calf stretch page covers a review comparing calf and plantar fascia stretching in heel pain³⁴. The broad definition of fascia includes tendons and ligaments, and deep fascia wraps muscle^1,7.

Sources

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2. Zügel M, Maganaris CN, Wilke J, Jurkat-Rott K, Klingler W, Wearing SC, Findley T, Barbe MF, Steinacker JM, Vleeming A, Bloch W, Schleip R, Hodges PW (2018). Fascial tissue research in sports medicine: from molecules to tissue adaptation, injury and diagnostics: consensus statement.. British Journal of Sports Medicine. doi:10.1136/bjsports-2018-099308 PMID 30072398
3. Wilke J, Krause F, Vogt L, Banzer W (2016). What Is Evidence-Based About Myofascial Chains: A Systematic Review.. Archives of Physical Medicine and Rehabilitation. doi:10.1016/j.apmr.2015.07.023 PMID 26281953
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12. Stecco C, Fede C, Macchi V, Porzionato A, Petrelli L, Biz C, Stern R, De Caro R (2018). The fasciacytes: A new cell devoted to fascial gliding regulation.. Clinical Anatomy. doi:10.1002/ca.23072 PMID 29575206
13. Suarez-Rodriguez V, Fede C, Pirri C, Petrelli L, Loro-Ferrer JF, Rodriguez-Ruiz D, De Caro R, Stecco C (2022). Fascial Innervation: A Systematic Review of the Literature.. International Journal of Molecular Sciences. doi:10.3390/ijms23105674 PMID 35628484
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15. Wilke J, Macchi V, De Caro R, Stecco C (2019). Fascia thickness, aging and flexibility: is there an association?. Journal of Anatomy. doi:10.1111/joa.12902 PMID 30417344
16. Warneke K, Rabitsch T, Dobert P, Wilke J (2024). The effects of static and dynamic stretching on deep fascia stiffness: a randomized, controlled cross-over study.. European Journal of Applied Physiology. doi:10.1007/s00421-024-05495-2 PMID 38689040
17. Krause F, Wilke J, Vogt L, Banzer W (2016). Intermuscular force transmission along myofascial chains: a systematic review.. Journal of Anatomy. doi:10.1111/joa.12464 PMID 27001027
18. Ajimsha MS, Shenoy PD, Surendran PJ, Jacob P, Bilal MJ (2022). Evidence of in-vivo myofascial force transfer in humans- a systematic scoping review.. Journal of Bodywork and Movement Therapies. doi:10.1016/j.jbmt.2022.05.006 PMID 36180147
19. Kretschmer L, Wilke J (2026). Remote Changes of Mechanical Stiffness Following Local Stretching or Contraction: A Systematic Review with Meta-Analysis.. Sports Medicine - Open. doi:10.1186/s40798-026-01030-z PMID 42228239
20. Burk C, Perry J, Lis S, Dischiavi S, Bleakley C (2020). Can Myofascial Interventions Have a Remote Effect on ROM? A Systematic Review and Meta-Analysis.. Journal of Sport Rehabilitation. doi:10.1123/jsr.2019-0074 PMID 31629335
21. Pollock N, James SL, Lee JC, Chakraverty R (2014). British athletics muscle injury classification: a new grading system.. British Journal of Sports Medicine. doi:10.1136/bjsports-2013-093302 PMID 25031367
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23. Rhim HC, Kwon J, Park J, Borg-Stein J, Tenforde AS (2021). A Systematic Review of Systematic Reviews on the Epidemiology, Evaluation, and Treatment of Plantar Fasciitis.. Life (Basel). doi:10.3390/life11121287 PMID 34947818
24. Schleip R, Overmann L, Müller M, Warneke K, Siegel SD, Bartsch K, Pohl T, Bensamoun S, Haiat G, Brandl A (2026). Thoracolumbar fascia ultrasound and elastography biomarkers in low back pain: a systematic review of associations and responsiveness to intervention.. European Spine Journal. doi:10.1007/s00586-026-10298-4 PMID 42645548
25. Kjaer M, Magnusson P, Krogsgaard M, Boysen Møller J, Olesen J, Heinemeier K, Hansen M, Haraldsson B, Koskinen S, Esmarck B, Langberg H (2006). Extracellular matrix adaptation of tendon and skeletal muscle to exercise.. Journal of Anatomy. doi:10.1111/j.1469-7580.2006.00549.x PMID 16637870
26. Akdemir Z, Özkan Z, Orak S, Arslan H, Akdeniz H, Kaplan Ş (2026). Shear wave elastography of the plantar fascia: A cross-sectional observational study in asymptomatic runners and sedentary controls.. Medicine (Baltimore). doi:10.1097/MD.0000000000047970 PMID 41790681
27. Chaudhry H, Schleip R, Ji Z, Bukiet B, Maney M, Findley T (2008). Three-dimensional mathematical model for deformation of human fasciae in manual therapy.. The Journal of the American Osteopathic Association. doi:10.7556/jaoa.2008.108.8.379 PMID 18723456
28. Laimi K, Mäkilä A, Bärlund E, Katajapuu N, Oksanen A, Seikkula V, Karppinen J, Saltychev M (2018). Effectiveness of myofascial release in treatment of chronic musculoskeletal pain: a systematic review.. Clinical Rehabilitation. doi:10.1177/0269215517732820 PMID 28956477
29. Behm DG, Wilke J (2019). Do Self-Myofascial Release Devices Release Myofascia? Rolling Mechanisms: A Narrative Review.. Sports medicine (Auckland, N.Z.). doi:10.1007/s40279-019-01149-y PMID 31256353
30. Katolicka T, Quittkova A, Pirri C, Stecco C, Katolicky J, Safarova M, Machac S (2026). Ultrasound assessment of deep fascia of lower limbs in children: an anatomical study.. Surgical and Radiologic Anatomy. doi:10.1007/s00276-026-03875-1 PMID 41934479
31. Fairclough J, Hayashi K, Toumi H, Lyons K, Bydder G, Phillips N, Best TM, Benjamin M (2006). The functional anatomy of the iliotibial band during flexion and extension of the knee: implications for understanding iliotibial band syndrome.. Journal of anatomy. doi:10.1111/j.1469-7580.2006.00531.x PMID 16533314
32. Friede MC, Innerhofer G, Fink C, Alegre LM, Csapo R (2022). Conservative treatment of iliotibial band syndrome in runners: Are we targeting the right goals?. Physical therapy in sport : official journal of the Association of Chartered Physiotherapists in Sports Medicine. doi:10.1016/j.ptsp.2021.12.006 PMID 35007886
33. Willard FH, Vleeming A, Schuenke MD, Danneels L, Schleip R (2012). The thoracolumbar fascia: anatomy, function and clinical considerations.. Journal of Anatomy. doi:10.1111/j.1469-7580.2012.01511.x PMID 22630613
34. Sweeting D, Parish B, Hooper L, Chester R (2011). The effectiveness of manual stretching in the treatment of plantar heel pain: a systematic review.. Journal of foot and ankle research. doi:10.1186/1757-1146-4-19 PMID 21703003

Every source the library cites

Changes

• September 30, 2026 First published.