What is Fascia? (Fascia Facts Part 1)

Fascia.  An up and coming buzzword that’s attracting a lot of attention.  When explaining fascia to people I describe it as that white filmy stuff that wraps around meat (muscle).  In some places it’s thin and wispy, while elsewhere very tough and thick.

Deer tenderloin with fascial layers
Figure 1: Here my husband, Bill, is cleaning a deer tenderloin. He’s lifting up the superficial fascia, which is fragile and easy to separate. Underneath is the deep fascia which is much denser and firmly adhered to the muscle. The deep layer looks like one thick layer, but it is actually multiple layers of criss-crossing collagen fiber bundles. If you look at it closely you may be able to identify these crossing fibers.

Fascia can be easily lifted from the muscle in some parts of the anatomy, yet in other places it’s so firmly attached that separating it requires cutting into the muscle fibers (the parts of the steak you throw to the dog).  These differences – called regional specialization – are based on location in the body and reflect the different roles the fascia fulfills according to the demand placed on it.  For example, the iliotibial band (ITB or IT band) running down the outer part of the thigh is one of the thickest, toughest pieces of fascia in the body.  The high forces transmitted throughout the lower limb require such a design.  By contrast, the fascia of the inner part of the arm or forearm is not nearly as thick as the ITB since it does not handle the same amount of load. 

The literature on fascia has been very confusing over the years, which has not helped our understanding of this connective tissue.  As often happens, people like to name things after themselves and fascial anatomy is no different.  This has led to multiple different names for fascia throughout areas like, for example, the abdomen and pelvis.  Not only is this confusing, but it also gives the false impression that these differently named regions of fascia are separate structures, when they are actually one seamless network.  From head to toe, right to left, front to back, the fascia is continuous, intermingling, and creates relationships throughout the body:  between the shoulder and the shin, the hand and the head, even the back and the bladder.      

When looked at with the naked eye or even under a microscope fascia can look very disorganized and messy, like the deep fascia on the deer tenderloin in Figure 1.  This is why some sources categorize deep fascia as irregular dense connective tissue.  But when separated by layer, it is actually found to be quite orderly with collagen fiber bundles laid down in a very organized manner, parallel to each other within that layer like fingers on a hand.

Fingers depicting collagen fiber bundles lying parallel within layer
Hands depicting space between fascial layers
Figures 2a & 2b: Appreciating the layered formation of the fascia is key to understanding how this tissue functions, what can go wrong, and how to fix it. The collagen fiber bundles in each layer lie parallel to each other, much like my fingers. But in the next layer those collagen fibers are oriented in a different direction. They are thought to govern movement according to the orientation of the fibers in each layer, and require separation (space) and lubrication (slide) between the layers.
Macroscopic and microscopic images of layered formation of fascia.
Figure 3: This is a wonderful depiction and explanation of the layered formation of the deep fascia, taken from the article “Fascia: The Forgotten Structure.” Used with permission from Carla Stecco, MD.

Fascia is made of many cells (essential for the life of the tissue), fibers (primarily collagen and elastin or elastic which provide structure and support), and a ground substance uniting it all (water, ions, and glycosaminoglycans or GAGS which make it adaptable).

Depiction of layers from skin to muscle
Figure 4: I call this the lasagna slice, complete with hair. Basically you can follow the layers from skin down to muscle. It’s not apparent in this drawing but the thinner white layer closer to the skin (labeled the superficial fascia) is really two layers. The thick, white layer of deep fascia on top of the muscle is actually 2-3 layers of fascia. These are separated by loose connective tissue full of hyaluronan, here labeled as the hyaluronic acid layer. It’s really not such a neat, isolated layer as depicted in yellow here, but more densely scattered between each of the deep fascia layers. When properly functioning it serves to provide space and slide between these layers. (Original source unknown.)

The layered formation of the fascia has only recently been demonstrated by researchers.  The superficial fascia has two tissue layers, while the deep fascia has two to three layers according to body region.

Picture of real time ultrasound showing tissue layers of thigh
Figure 5: Ultrasound image of the tissue layers of the thigh. Here the space between the layers is much more visible than in Figure 3. Normal functioning of structures (muscles, nerves, blood vessels, organs, etc.) relies on the integrity of this spacing in the nearby fascial layers, as well as the associated slide between the layers. Courtesy of Antonio Stecco, MD, PhD.

  They are separated by layers of loose connective tissue (LCT), which has a very high content of elastic, water, and a substance known as hyaluronan (also called hyaluronic acid or HA).   This is our body’s biochemical lubricant that provides space and slide between tissue layers. HA is found in connective tissues throughout the body, and also happens to be an ingredient used in injections to help joints move better, like the knee.  The integrity of this sliding system is thought to be key to pain free movement of joints and overall function. 

Fascia is loaded with nerves, which is another feature we have only recently come to appreciate.

Microscopic innervation of deep fascia
Figure 6: Dissection, staining, and magnification of the deep fascia demonstrate the presence of many nerve endings that perceive temperature, pressure, movement, and noxious stimuli that can potentially produce pain. The body would not harbor these structures in the fascia unless they served a purpose, namely for perceiving information about the status of the body. Used with permission from Carla Stecco, MD.

  Chemical staining of the fascia and viewing slices under a microscope reveal the presence of a variety of nerves that perceive pressure, stretch, temperature, and pain.  This is remarkable to comprehend, as fascia has historically been considered a tissue existing primarily for containment purposes – not a potential source of pain!  Once again, the demand dictates the structure: body regions that need more information in order to keep us safe and functioning (wrist, ankle) have a higher content of nerves in the fascia as compared to areas like the elbow and knee, which are better suited for stabilization.  In the muscles, fascia is connected to the portion of the nerve that turns it on (muscle spindle).  Conversely, near the tendons the fascia communicates with the mechanism that turns it off (golgi tendon organ or GTO).  Fascia surrounds the nerves to protect, cushion, and facilitate glide for pain free mobility and function.

Fascial layers provide protection to nerves
Figure 7: The fascia and loose connective tissue between the fascial layers serve to cushion and protect a nerve as it passes through an area, while also facilitating pain free movement of the nerve. In this publication the research team at the University of Padova, Italy, demonstrated such a relationship between the musculocutaneous nerve of the arm and the surrounding connective tissue. Used with permission from Carla Stecco, MD.

Nerves also have to pass through the layers of fascia to reach their target structure:  skin, muscles, blood vessels, sweat and oil glands just to name a few of the structures the nerves communicate with.

Points of potential entrapment as nerves travel to surface of skin
Figure 8: Schematic of multiple potential sites of nerve entrapment along the route to a target tissue. We often focus on the larger nerves such as the sciatic in the leg or the median in the carpal tunnel. But it’s good to appreciate that countless small nerves traverse through these layers, making their way to the surface to give us the sensations of cold/heat, pressure, movement, and pain. Taken from the article “Fascial Entrapment Neuropathy,” and used with permission from Dr. Antonio Stecco, MD, PhD.

  Internal organs like our stomach, bladder, ovaries, prostate, and intestines are lined with fascia full of nerves which coordinate the involuntary, autonomic functions these organs fulfill.  

Depiction of fascia, nerves, and stomach
Figure 9: The relationship of the fascia, autonomic nervous system, and internal organs is extremely complex. Here the stomach is depicted with its associated fascia that penetrates into the walls lining the stomach. The nerves embedded in this fascia orchestrate the precise timing of the movement of food to different parts of the stomach as it is processed. The integrity of this timing depends on the associated fascia functioning normally. Used with permission from Antonio Stecco, MD, PhD.

This post is part of a series explaining fascia. Read the rest of the series here: Where is Fascia found? and What can go wrong with the Fascia? The posts are combined on the page Fascia Facts.

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Published by Colleen Murphy Whiteford

I am a physiotherapist, graduate of Saint Louis University Class of 1984. I married my best friend and business partner, Bill, who is also a physiotherapist, in 1988. We have worked together all these years - an example of God's grace! Together we started Appalachian Physical Therapy which continues to thrive. I am a big believer in the power of touch, the manual therapies, and treating holistically. There are many alternatives to medications, surgeries, and testing, but people are often uninformed. My perspective emphasizes the role of the connective tissues including the fascia. Lack of attention to this structure is the source of many physical ailments - our bodies are truly fearfully and wonderfully made (Psalm 139)! I am passionate about helping people of all ages and diagnoses maximize their health, and empowering them to understand their role in management and prevention of problems.

2 thoughts on “What is Fascia? (Fascia Facts Part 1)

    1. Marge is that you??? How great to hear from you! This is an old post, the rest of it can be found in subsequent posts as well as all combined in a page under Fascia Facts. Thanks for reading, hope you guys are well, would love to reconnect!

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