Connective tissue is composed of cells (including fibroblasts and chondrocytes) and an extracellular matrix of collagen and elastic fibers surrounded by a ground substance made primarily of acid glycosaminoglycans (AGAGs) and water (Gray's anatomy 1995, Lederman 1997). Its patterns of deposition change from location to location, depending upon its role and the stresses applied to it.
The collagen component is composed of three polypeptide chains wound around each other to form triple helixes. These
microfilaments are arranged in parallel manner and bound together by crosslinking hydrogen bonds, which 'glue' the elements together to provide strength and stability when mechanical stress is applied. Movement encourages the collagen fibers to align themselves along the lines of structural stress as well as improves the balance of glycosaminoglycans and water, therefore lubricating and hydrating the connective tissue (Lederman 1997).
While these bonding crossbridges do provide structural support, injury, chronic stress and immobility cause excessive bonding, leading to the formation of scars and adhesions which limit the movement of these usually resilient tissues (Julian 1987). The loss of tissue lengthening potential would then not be due to the volume of collagen but to the random pattern in which it is laid down and the abnormal crossbridges which prevent normal movement. Following tissue injury, it is important that activity be introduced as soon as the healing process will allow in order to prevent maturation of the scar tissue and development of adhesive crosslinks (Lederman 1997).
Lederman (1997) tells us:
The pattern of collagen deposition varies in different types of connective tissue. It is an adaptive process related to the direction of forces imposed on the tissue. In tendon, collagen fibers are organized in parallel arrangement; this gives the tendon stiffness and strength under unidirectional loads. In ligaments, the organization of the fibers is looser, groups of fibers lying in different directions. This reflects the multidirectional forces that ligaments are subjected to, for example during complex movements of a joint such as flexion combined with rotation and shearing ... Elastin has an arrangement similar to
and its deposition is also dependent on the mechanical stresses imposed on the tissue.
Elastin provides an elastic-like quality which allows the connective tissue to stretch to the limit of the collagen fiber's length, while absorbing tensile force. If this elastic quality is stretched over time, it may lose its ability to recoil (as seen in the stretch marks of pregnancy). When stress is applied, the tissue can be stretched to the limit of the collagen fiber length with flexibility being dependent upon elastic quality (and quantity) as well as the extent of crossbridging which has occurred between the collagen fibers. Additionally, if heavy pressure is suddenly applied, the connective tissue may respond as brittle and may more easily tear (Kurz 1986).
Surrounding the collagen and elastic fibers is a viscous, gel-like ground substance, composed of proteoglycans and hyaluronan (formerly called hyaluronic acid), which lubricates these fibers and allows them to slide over one another (Barnes 1990, Gray's anatomy 1995).
โข Ground substances provides the immediate environment for every cell in the body.
โข The protein component is hydrophilic (draws water into the tissue), producing a cushion effect as well as maintaining space between the collagen fibers.
โข Ground substance provides the medium through which other elements are exchanged, such as gases, nutrients, hormones, cellular waste, antibodies and white blood cells (Juhan 1987).
โข The condition of the ground substance can then affect the rate of diffusion and therefore the health of the cells it surrounds.
Juhan (1987) notes:
Where we find mostly fluid and few fibers, we have a watery intercellular medium that is ideal for metabolic activities; with less fluid and more fibers, we have a soft, flexible lattice that can hold skin cells or liver cells or nerve cells into place; with little fluid and many fibers, we have the tough, stringy material of muscle sacs, tendons, and ligaments. If chondroblasts (cartilage-producing cells) and their hyaline secretions are added to this matrix, we obtain more solidity, and in the bones this cartilaginous secretion is replaced by mineral salts to achieve a rock-like hardness.
Unless irreversible fibrotic changes have occurred or other pathologies exist, connective tissue's state can be changed from a gelatinous-like substance to a more solute (watery) state by the introduction of energy through muscular activity (active or passive movement provided by activity or stretching), soft tissue manipulation (as provided by massage) or heat (as in hydrotherapies). This characteristic, called thixotropy, is 'a property of certain gels of becoming less viscous when shaken or subjected to shearing forces and returning to the original viscosity upon standing' (Stedman's 1998). Without thixotropic properties, movement would eventually cease due to solidification of synovium and connective tissue.
Oschman states (1997):
If stress, disuse and lack of movement cause the gel to dehydrate, contract and harden (an idea that is supported both by scientific evidence and by the experiences of many soma to-therapists) the application of pressure seems to bring about a rapid solation and rehydration. Removal of the pressure allows the system to rapidly re-gel, but in the process the tissue is transformed, both in its water