fascia

Fascia is a band or sheet of connective tissue that ensheathes, binds together, and separates muscles and other structures throughout the body. It forms a continuous three-dimensional network that extends from the skin to internal organs, transmitting forces produced by muscles and providing structural integrity to the body.

Fascia is traditionally described in three functional layers: superficial fascia, deep fascia, and visceral (or subserous) fascia. Superficial fascia lies just beneath the skin and contains fat and cutaneous nerves. Deep fascia is a dense network that wraps individual muscles, muscle groups, and neurovascular bundles; it also forms retinacula around joints and contributes to the formation of anatomical compartments. Visceral fascia surrounds and supports organs and body cavities, helping to anchor them in place.

Fascia is composed mainly of collagen fibers arranged in layered sheets within an extracellular matrix of proteoglycans and water. It includes elastin for some elasticity and a rich innervation with mechanoreceptors, supporting proprioception and reflex control. The properties of fascia are viscoelastic, allowing gradual stretching (creep) and dynamic adaptation to movement and loading.

Functions include mechanical support and force transmission between muscles, compartmentalization to optimize movement, protection of vessels and nerves, and facilitation of inter-tissue sliding. It also plays a role in mechanical signaling and proprioception through its innervation.

Clinical relevance involves fascial dysfunction associated with pain and restricted mobility; conditions such as myofascial pain syndrome, fascial thickening, and adhesions may occur after injury or surgery. Manual therapies claiming to release fascia are used clinically, though evidence varies by technique. In practice, surgeons often dissect along fascial planes to avoid damage; fascia can heal slowly in injured areas due to relatively limited vascularity. Imaging methods such as ultrasound and MRI can assess fascial thickening or edema in certain disorders.