Connective Tissue

There are only four types of human tissue. We cover muscle and nerve tissue elsewhere and epithelial tissue, while being prolific throughout the body, is less relevant to our discussion. Connective tissue however is very relevant.
Function

In order for us to move, or even stand, a number of things have to happen.

• The nervous system triggers an electrical response in muscle tissue to contract.
• Chemical energy is released, and muscle fibres contract with enough force to move and stabilise joint structures.
• This force is transferred to the bone along a continuous matrix of connective tissue. The fascia deep within the muscle extends to the extremity to become tendon and is eventually connected to the supporting fascia of the bone to which it attaches.
• Contraction in opposing muscle groups enable us to move and maintain stable postures

So the fascia has two roles, it connects physically and it facilitates mechanically in the transformation of chemical energy stored in the muscle to the movement of the bone. (It has other functions too they are less relevant to this discussion.)
Structure

Connective tissue is made up, to varying degrees, of fibrous substances called collagen which gives it strength, and elastin which (surprise, surprise) adds elasticity to the tissue, embedded in a matrix of either fluid, solid or gel. The type of matrix and the relative mix of collagen and elastin reflects a phenomenon that exists throughout the body, that is the constant trade-off between strength and flexibility. Tissues rich in collagen tend to be thicker and less flexible but stronger while those with relatively less collagen are more flexible but can't take as much force as they would otherwise.

The structure of thefascia reflects this trade-off. Force is a product of magnitude and direction, the magnitude will determine the thickness of the fascia, that is the density of collagen fibres, while the direction of the force affects the arrangement of the fibres. Broad flat sheets of superficial fascia tend to have fewer collagen fibres that are arranged quite randomly while tendons are thicker and their fibres are mainly parallel, consistent with a more unidirectional force.

Collagen fibres provide tensile strength to the tissue. The forces applied to this tissue determine the density and arrangement of these collagen fibres.
Overuse

Connective tissue responds to the loads placed on it. When a muscle is overused the connective tissue component has more work to do so it lays down more collagen fibres in the direction that the forces are applied. This alignment however depends on the tissue being well hydrated, if it is not the collagen fibres will be laid down more randomly. When they are also densely packed in irregular patterns tendons become thick and inflexible.

Stretching and certain types of massage will encourage both hydration and tension along the line of force of the muscle, encouraging the more regular parallel alignment of collagen fibres required at healthy tendons.

The physiology of tendon injuries is not completely understood but it is now well accepted that both the density and arrangement of collagen fibres is an important factor. Refer to the section on Cumulative Trauma Disorders.