Stretching is the process by which a force is applied either passively or actively to tissue to elongate the musculotendinous unit. The result of this elongation is an increase in range of motion. Most of the resistance is not in the actual muscle tissue itself, but the connective tissue framework in and around the muscle tissue. Connective tissue is made up of non-elastic collagen fibers and a small amount of elastic fibers within a protein matrix. Connective tissue has the ability to support and protect underlying structures from injury due to its high tensile strength.
Connective tissue is classed as visco-elastic.
This means that it has properties of elasticity and viscosity. Elastic stretch is an elongation of tissue that bounces back when the tension is removed. This stretch is sometimes referred to as a temporary stretch. This condition is classed as permanent. Tissue that is stretched too vigorously or for a prolonged period of time can lead to serious injury.