Towards a comprehensive definition of the human fascial system.

The absence of a clear consensus on the definition and significance of fascia and the indiscriminate use of the term throughout the clinical and scientific literature has led to skepticism regarding its importance in the human body. To address this challenge, we propose that: (1) fasciae, and the fascial interstitia within them, constitute an anatomical system, defined as a layered body-wide multiscale network of connective tissue that allows tensional loading and shearing mobility along its interfaces; (2) the fascial system comprises four anatomical organs: the superficial fascia, musculoskeletal (deep) fascia, visceral fascia, and neural fascia; (3) these organs are further composed of anatomical structures, some of which are eponymous; (4) all these fascial organs and their structural components contain variable combinations and arrangements of the four classically defined tissues: epithelial, connective, muscle, and neural; (5) the overarching functions of the fascial system arise from the contrasting biomechanical properties of the two basic types of layers distributed throughout the system: one predominantly collagenous and relatively stiff, the other rich in hyaluronic acid and viscous, allowing for the free flow of fluid; (6) the topographical organization of these layers in different locations is related to local variations in function (e.g. unidirectional arrangements favor tensional loading, interwoven structures favor shear mobility) thereby accounting for both the system's universal functional aspects and the site-specific variations between them. A universal language related to fascia will break down linguistic barriers and facilitate cross-disciplinary cooperation, enabling scientists and practitioners from diverse backgrounds to contribute their expertise seamlessly.