Connective tissue is the most widespread and abundant type of tissue in the human body and encompasses far more tissue than most realize. In the fitness industry, we primarily think of fascia, ligaments, and tendons first, but under the expansive umbrella of connective tissue (CT), you’ll also find bone, cartilage, blood, lymph, and even adipose.
Types of Connective Tissue
The nature of connective tissue and its function continues to be somewhat scientifically elusive. There are disagreements about its function, its impact, and its role in complex movement and pain syndromes.
There are three main morphological groups of CT. Since mechanical testing on live subjects has proven to be complicated, apply these designations somewhat loosely :
- Loose connective tissue keeps organs in place and attaches epithelial tissue to other tissues.
- Dense connective tissue are your tendons and ligaments—-attaching muscles to bones and bone to bone.
- Specialized connective tissue are the wildcards in the bunch, encompassing several different specialized tissues of varying consistencies and serving various functions. These include adipose, cartilage, bone, blood, and lymph tissue.
Loose and dense tissue are made up of collagen fibers, reticular fibers, and elastin fibers.
- Collagenous fibers as the name implies are comprised of collagen–a protein–that form bundles of long, thick bands called fibrils which give CT its strength.
- Elastic fibers are made of the stretchable protein elastin lending to—you guessed it—elasticity.
- Reticular fibers join CT to other tissues.
Furthermore, each group can be defined by its relationship to the skin: superficial or deep. This is keeping a complex anatomical subject as simple as possible. Below is a table describing more in-depth the categories and descriptors of all the human body’s CT:
Table of Terms
|Dense connective tissue||CT containing closely packed, irregularly arranged (that is, aligned in many directions) collagen fibers.|
|Non-dense (areolar) connective tissue||CT containing sparse, irregularly arranged collagen fibers.|
|Superficial fascia||Enveloping layer directly beneath the skin containing dense and areolar CT and fat.|
|Deep fascia||Continuous sheet of mostly dense, irregularly arranged CT that limits the changes in shape of underlying tissues. Deep fasciae may be continuous with epimysium and intermuscular septa and may also contain layers of areolar CT.|
|Intermuscular septa||A thin layer of closely packed bundles of collagen fibers, possibly with several preferential directions predominating, arranged in various layers. The septa separate different, usually antagonistic, muscle groups (for example, flexors and extensors), but may not limit force transmission.|
|Interosseal membrane||Two bones in a limb segment can be connected by a thin collagen membrane with a structure similar to the intermuscular septa.|
|Periost||Surrounding each bone and attached to it is a bi-layered collagen membrane similar in structure to the epimysium.|
|Neurovascular tract||The extramuscular collagen fiber reinforcement of blood and lymph vessels and nerves. This complex structure can be quite stiff. The diameter and, presumably, the stiffness of neurovascular tracts decrease along limbs from proximal to distal parts. Their stiffness is related to the angle or angles of the joints that they cross.|
|Epimysium||A multi-layered, irregularly arranged collagen fiber sheet that envelopes muscles and that may contain layers of both dense and areolar CT.|
|Intra- and extramuscular aponeurosis||A multilayered structure with densely laid down bundles of collagen with major preferential directions. The epimysium also covers the aponeuroses, but is not attached to them. Muscle fibers are attached to intramuscular aponeuroses by their myotendinous junctions.|
|Perimysium||A dense, multi-layered, irregularly arranged collagen fiber sheet that envelopes muscle fascicles. Adjacent fascicles share a wall of the tube (like the cells of a honeycomb).|
|Endomysium||Fine network of irregularly arranged collagen fibers that form a tube enveloping and connecting each muscle fiber. Adjacent muscle fibers share a wall of the tube (like the cells of a honeycomb).|
Table courtesy Langevin and Huijing (2009)
Fitness professionals would benefit most from understanding intimately loose and dense connective tissue. CT that is well vascularized is far less likely to tear or rupture under extreme stress – a desirable characteristic when performing any kind of physical activity. The following blogs in this series will look more closely at loose and dense CT: fascia, tendons and ligaments.