Plasticity is at the far end of the spectrum from elasticity. It is the quality of a connective tissue, such as a ligament or tendon, when subjected to ballistic, prolonged, or sudden forces exceeding the elastic limits of the tissue. The tissue does not return to its original state after the deforming load is removed. The anatomical plastic region (APR) of connective tissue is found between 6% and 10% of the ligament’s or tendon’s resting length, and is at the very wall of failure (to the maximum tissue tensile strength).
From plasticity, we learn that some tissues are less injury prone when stressed rapidly. For instance, ligaments are composed of wavy collagen fibers. Uncoiled, the fibers become taught and susceptible to injury. If taken into the APR, a ligament tears. Whereas slow loading causes uncoiling through taking the slack out of the fibers, quick loading does not allow sufficient time for a ligament to enter the APR.
The properties of cartilage make it equally less injury prone when quickly loaded. Cartilage decreases the stress in a joint by decreasing the friction coefficient between bones and through distributing load over the surface of the joint complex. Cartilage is composed of 20-40% collagen and 60-80% water. With predictability, cartilage behaves with the properties of water in a sponge. When it is compressed it decreases the protection between bones. However, with rapid loading the fluid does not have sufficient time to be squeezed out and the shock absorption is maximal.
Discomfort is productive; pain is unproductive. This statement is completely subjective, and there must be a dialogue/feedback between our teacher and ourselves, or at the very least between our journal or web log and ourselves.
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